Ivan Marusic

A scheme to correct the influence of calibration misalignment for cross-wire probes in turbulent shear flows

Publisher: Springer Science and Business Media LLC

Date: 03-2020

DOI: 10.1007/S00348-020-2918-8

Minimum Sustainable Drag for Constant Volume-Flux Pipe Flows

Publisher: Springer Netherlands

Date: 2008

DOI: 10.1007/978-1-4020-6858-4_27

Conditionally averaged flow topology about a critical point pair in the skin friction field of pipe flows using direct numerical simulations

Publisher: American Physical Society (APS)

Date: 28-11-2018

DOI: 10.1103/PHYSREVFLUIDS.3.114607

Turbulence in the Era of Big Data: Recent Experiences with Sharing Large Datasets

Publisher: Springer International Publishing

Date: 31-08-2016

DOI: 10.1007/978-3-319-41217-7_27

Reynolds Number Invariance of the Structure Inclination Angle in Wall Turbulence

Publisher: American Physical Society (APS)

Date: 14-09-2007

DOI: 10.1103/PHYSREVLETT.99.114504

Active and inactive components of the streamwise velocity in wall-bounded turbulence

Publisher: Cambridge University Press (CUP)

Date: 05-03-2021

DOI: 10.1017/JFM.2020.884

Amplitude modulation of all three velocity components in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 31-03-2014

DOI: 10.1017/JFM.2014.132

Abstract: A combination of cross-wire probes with an array of flush-mounted skin-friction sensors are used to study the three-dimensional conditional organisation of large-scale structures in a high-Reynolds-number turbulent boundary layer. Previous studies have documented the litude modulation of small-scale motions in response to conditionally averaged large-scale events, but the data are largely restricted to the streamwise component of velocity alone. Here, we report results based on all three components of velocity and find that the small-scale spanwise and wall-normal fluctuations ( $v$ and $w$ ) and the instantaneous Reynolds shear stress ( $-{uw}$ ) are modulated in a very similar manner to that previously noted for the streamwise fluctuations ( $u$ ). The envelope of the small scale fluctuations for all velocity components is well described by the large-scale component of the $u$ fluctuation. These results also confirm the conditional existence of roll modes associated with the very large-scale or ‘superstructure’ motions.

The anisotropic structure of turbulence and its energy spectrum

Publisher: AIP Publishing

Date: 2016

DOI: 10.1063/1.4939471

Abstract: The spectral energy distribution in turbulent flows is observed to follow a k−5/3 power scaling, as originally predicted by Kolmogorov’s theory. However, the underlying assumptions in Kolmogorov’s theory appear not to hold with most experimental and numerical data showing evidence of small-scale anisotropy and significant direct energy transfer between the large- and the small-scales. Here, we present a flow structure that reconciles the k−5/3 spectrum with small-scale universality, small-scale anisotropy, and direct scale interactions. The flow structure is a shear layer, which contains the small-scales of motion and is bounded by the large-scales. The anisotropic shear layer reveals the expected scaling of the energy spectrum in nearly all directions.

High spatial range velocity measurements in a high Reynolds number turbulent boundary layer

Publisher: AIP Publishing

Date: 02-2014

DOI: 10.1063/1.4866458

Abstract: Here, we detail and analyse a multi-resolution particle image velocity measurement that resolves the wide range of scales prevalent in a zero pressure gradient turbulent boundary layer at high Reynolds numbers (up to Reτ ≈ 20 000). A unique configuration is utilised, where an array of eight high resolution cameras at two magnification levels are used simultaneously to obtain a large field of view, while still resolving the smaller scales prevalent in the flow. Additionally, a highly magnified field of view targeted at the near wall region is employed to capture the viscous sublayer and logarithmic region, with a spatial resolution of a few viscous length scales. Flow statistics from these measurements show good agreement with prior, well resolved hot-wire anemometry measurements. Analysis shows that the instantaneous wall shear stress can be reliably computed, which is historically known to be challenging in boundary layers. A statistical assessment of the wall shear stress shows good agreement with existing correlations, prior experimental and direct numerical simulation data, extending this view to much higher Reynolds numbers. Furthermore, conditional analysis using multiple magnification levels is detailed, to study near-wall events associated with high skin friction fluctuations and their associated overlaying structures in the log region. Results definitively show that the passage of very large-scale positive (or negative) velocity fluctuations are associated with increased (or reduced) small-scale variance in wall shear stress fluctuations.

A comparison of turbulent pipe, channel and boundary layer flows

Publisher: Cambridge University Press (CUP)

Date: 27-07-2009

DOI: 10.1017/S0022112009007423

Abstract: The extent or existence of similarities between fully developed turbulent pipes and channels, and in zero-pressure-gradient turbulent boundary layers has come into question in recent years. This is in contrast to the traditionally accepted view that, upon appropriate normalization, all three flows can be regarded as the same in the near-wall region. In this paper, the authors aim to provide clarification of this issue through streamwise velocity measurements in these three flows with carefully matched Reynolds number and measurement resolution. Results show that mean statistics in the near-wall region collapse well. However, the premultiplied energy spectra of streamwise velocity fluctuations show marked structural differences that cannot be explained by scaling arguments. It is concluded that, while similarities exist at these Reynolds numbers, one should exercise caution when drawing comparisons between the three shear flows, even near the wall.

Sensitivity of turbulent stresses in boundary layers to cross-wire probe uncertainties in the geometry and calibration procedure

Publisher: IOP Publishing

Date: 07-2019

DOI: 10.1088/1361-6501/AB1491

Progress in Wall Turbulence: Understanding and Modeling

Publisher: Springer Netherlands

Date: 2011

DOI: 10.1007/978-90-481-9603-6

Quantifying inner-outer interactions in noncanonical wall-bounded flows

Publisher: American Physical Society (APS)

Date: 21-08-2023

DOI: 10.1103/PHYSREVFLUIDS.8.084602

Velocity probability distribution scaling in wall-bounded flows at high Reynolds numbers

Publisher: American Physical Society (APS)

Date: 07-03-2019

DOI: 10.1103/PHYSREVFLUIDS.4.034101

Extended self-similarity in moment-generating-functions in wall-bounded turbulence at high Reynolds number

Publisher: American Physical Society (APS)

Date: 09-08-2016

DOI: 10.1103/PHYSREVFLUIDS.1.044405

Global and local aspects of entrainment in temporal plumes

Publisher: Cambridge University Press (CUP)

Date: 22-12-2016

DOI: 10.1017/JFM.2016.786

Abstract: To date, the understanding of the role buoyancy plays in the entrainment process in unstable configurations such as turbulent plumes remains incomplete. Towards addressing this question, we set up a flow in which a plume evolves in time instead of space. We demonstrate that the temporal problem is equivalent to a spatial plume in a strong coflow and address in detail how the temporal plume can be realized via direct numerical simulation. Using numerical data of plume simulations up to $Re_{\\unicode[STIX]{x1D706}}\\approx 100$ , we show that the entrainment coefficient can be determined consistently using a global entrainment analysis in an integral framework as well as via a local approach. The latter is based on a study of the local propagation of the turbulent/non-turbulent interface relative to the fluid. Locally, this process is dominated by small-scale diffusion which is lified by interface convolutions such that the total entrained flux is independent of viscosity. Further, we identify a direct buoyancy contribution to entrainment by baroclinic torque, which accounts for 8 %–12 % of the entrained flux locally, comparable to the 15 % buoyancy contribution at the integral level. It appears that the baroclinic torque is a mechanism that might explain higher values of the entrainment coefficient in spatial plumes compared with jets.

Australians’ views and experience of personal genomic testing: survey findings from the Genioz study

Publisher: Springer Science and Business Media LLC

Date: 21-01-2019

DOI: 10.1038/S41431-018-0325-X

A comparative study of the velocity and vorticity structure in pipes and boundary layers at friction Reynolds numbers up to

Publisher: Cambridge University Press (CUP)

Date: 23-04-2019

DOI: 10.1017/JFM.2019.182

Abstract: This study presents findings from a first-of-its-kind measurement c aign that includes simultaneous measurements of the full velocity and vorticity vectors in both pipe and boundary layer flows under matched spatial resolution and Reynolds number conditions. Comparison of canonical turbulent flows offers insight into the role(s) played by features that are unique to one or the other. Pipe and zero pressure gradient boundary layer flows are often compared with the goal of elucidating the roles of geometry and a free boundary condition on turbulent wall flows. Prior experimental efforts towards this end have focused primarily on the streamwise component of velocity, while direct numerical simulations are at relatively low Reynolds numbers. In contrast, this study presents experimental measurements of all three components of both velocity and vorticity for friction Reynolds numbers $Re_{\\unicode[STIX]{x1D70F}}$ ranging from 5000 to 10 000. Differences in the two transverse Reynolds normal stresses are shown to exist throughout the log layer and wake layer at Reynolds numbers that exceed those of existing numerical data sets. The turbulence enstrophy profiles are also shown to exhibit differences spanning from the outer edge of the log layer to the outer flow boundary. Skewness and kurtosis profiles of the velocity and vorticity components imply the existence of a ‘quiescent core’ in pipe flow, as described by Kwon et al. ( J. Fluid Mech. , vol. 751, 2014, pp. 228–254) for channel flow at lower $Re_{\\unicode[STIX]{x1D70F}}$ , and characterize the extent of its influence in the pipe. Observed differences between statistical profiles of velocity and vorticity are then discussed in the context of a structural difference between free-stream intermittency in the boundary layer and ‘quiescent core’ intermittency in the pipe that is detectable to wall distances as small as 5 % of the layer thickness.

Revisiting the law of the wake in wall turbulence

Publisher: Cambridge University Press (CUP)

Date: 13-12-2016

DOI: 10.1017/JFM.2016.788

Abstract: The streamwise mean velocity profile in a turbulent boundary layer is classically described as the sum of a log law extending all the way to the edge of the boundary layer and a wake function. While there is theoretical support for the log law, the wake function, defined as the deviation of the measured velocity profile from the log law, is essentially an empirical fit and has no real physical underpinning. Here, we present a new physically motivated formulation of the velocity profile in the outer region, and hence for the wake function. In our approach, the entire flow is represented by a two-state model consisting of an inertial self-similar region designated as ‘pure wall flow state’ (featuring a log-law velocity distribution) and a free stream state, which results in a jump in velocity at the interface separating the two. We show that the model provides excellent agreement with the available high Reynolds number mean velocity profiles if this interface is assumed to fluctuate randomly about a mean position with a Gaussian distribution. The new concept can also be extended to internal geometries in the same form, again confirmed by the data. Furthermore, adopting the same interface distribution in a two-state model for the streamwise turbulent intensities, with unchanged parameters, also yields a reliable and consistent prediction for the decline in the outer region of these profiles in all geometries considered. Finally, we discuss differences between our model interface and the turbulent/non-turbulent interface (TNTI) in turbulent boundary layers. We physically interpret the two-state model as lumping the effects of internal shear layers and the TNTI into a single discontinuity at the interface.

Pressure gradient effects on the large-scale structure of turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 09-01-2013

DOI: 10.1017/JFM.2012.531

Abstract: Research into high-Reynolds-number turbulent boundary layers in recent years has brought about a renewed interest in the larger-scale structures. It is now known that these structures emerge more prominently in the outer region not only due to increased Reynolds number (Metzger & Klewicki, Phys. Fluids , vol. 13(3), 2001, pp. 692–701 Hutchins & Marusic, J. Fluid Mech. , vol. 579, 2007, pp. 1–28), but also when a boundary layer is exposed to an adverse pressure gradient (Bradshaw, J. Fluid Mech. , vol. 29, 1967, pp. 625–645 Lee & Sung, J. Fluid Mech. , vol. 639, 2009, pp. 101–131). The latter case has not received as much attention in the literature. As such, this work investigates the modification of the large-scale features of boundary layers subjected to zero, adverse and favourable pressure gradients. It is first shown that the mean velocities, turbulence intensities and turbulence production are significantly different in the outer region across the three cases. Spectral and scale decomposition analyses confirm that the large scales are more energized throughout the entire adverse pressure gradient boundary layer, especially in the outer region. Although more energetic, there is a similar spectral distribution of energy in the wake region, implying the geometrical structure of the outer layer remains universal in all cases. Comparisons are also made of the litude modulation of small scales by the large-scale motions for the three pressure gradient cases. The wall-normal location of the zero-crossing of small-scale litude modulation is found to increase with increasing pressure gradient, yet this location continues to coincide with the large-scale energetic peak wall-normal location (as has been observed in zero pressure gradient boundary layers). The litude modulation effect is found to increase as pressure gradient is increased from favourable to adverse.

Dissipation scaling in constant-pressure turbulent boundary layers

Publisher: American Physical Society (APS)

Date: 07-03-2017

DOI: 10.1103/PHYSREVFLUIDS.2.032601

Use of direct numerical simulation (DNS) data to investigate spatial resolution issues in measurements of wall-bounded turbulence

Publisher: IOP Publishing

Date: 25-09-2009

DOI: 10.1088/0957-0233/20/11/115401

LES of the adverse-pressure gradient turbulent boundary layer

Publisher: Elsevier BV

Date: 12-2013

DOI: 10.1016/J.IJHEATFLUIDFLOW.2013.06.011

An extensional strain sensing mechanosome drives adhesion-independent platelet activation at supraphysiological hemodynamic gradients

Publisher: Springer Science and Business Media LLC

Date: 24-03-2022

DOI: 10.1186/S12915-022-01274-7

Abstract: Supraphysiological hemodynamics are a recognized driver of platelet activation and thrombosis at high-grade stenosis and in blood contacting circulatory support devices. However, whether platelets mechano-sense hemodynamic parameters directly in free flow (in the absence of adhesion receptor engagement), the specific hemodynamic parameters at play, the precise timing of activation, and the signaling mechanism(s) involved remain poorly elucidated. Using a generalized Newtonian computational model in combination with microfluidic models of flow acceleration and quasi-homogenous extensional strain, we demonstrate that platelets directly mechano-sense acute changes in free-flow extensional strain independent of shear strain, platelet lification loops, von Willebrand factor, and canonical adhesion receptor engagement. We define an extensional strain sensing “mechanosome” in platelets involving cooperative Ca 2+ signaling driven by the mechanosensitive channel Piezo1 (as the primary strain sensor) and the fast ATP gated channel P2X1 (as the secondary signal lifier). We demonstrate that type II PI3 kinase C2α activity (acting as a “clutch”) couples extensional strain to the mechanosome. Our findings suggest that platelets are adapted to rapidly respond to supraphysiological extensional strain dynamics, rather than the peak magnitude of imposed wall shear stress. In the context of overall platelet activation and thrombosis, we posit that “extensional strain sensing” acts as a priming mechanism in response to threshold levels of extensional strain allowing platelets to form downstream adhesive interactions more rapidly under the limiting effects of supraphysiological hemodynamics.

Reynolds-number-dependent turbulent inertia and onset of log region in pipe flows

Publisher: Cambridge University Press (CUP)

Date: 26-09-2014

DOI: 10.1017/JFM.2014.486

Abstract: A detailed analysis of the ‘turbulent inertia’ (TI) term (the wall-normal gradient of the Reynolds shear stress, $\\mathrm{d} \\langle -uv\\rangle /\\mathrm{d} y $ ), in the axial mean momentum equation is presented for turbulent pipe flows at friction Reynolds numbers $\\delta ^{+} \\approx 500$ , 1000 and 2000 using direct numerical simulation. Two different decompositions for TI are employed to further understand the mean structure of wall turbulence. In the first, the TI term is decomposed into the sum of two velocity–vorticity correlations ( $\\langle v \\omega _z \\rangle + \\langle - w \\omega _y \\rangle $ ) and their co-spectra, which we interpret as an advective transport (vorticity dispersion) contribution and a change-of-scale effect (associated with the mechanism of vorticity stretching and reorientation). In the second decomposition, TI is equivalently represented as the wall-normal gradient of the Reynolds shear stress co-spectra, which serves to clarify the accelerative or decelerative effects associated with turbulent motions at different scales. The results show that the inner-normalised position, $y_m^{+}$ , where the TI profile crosses zero, as well as the beginning of the logarithmic region of the wall turbulent flows (where the viscous force is leading order) move outwards in unison with increasing Reynolds number as $y_m^{+} \\sim \\sqrt{\\delta ^{+}}$ because the eddies located close to $y_m^{+}$ are influenced by large-scale accelerating motions of the type $\\langle - w \\omega _y \\rangle $ related to the change-of-scale effect (due to vorticity stretching). These large-scale motions of $O(\\delta ^{+})$ gain a spectrum of larger length scales with increasing $\\delta ^{+}$ and are related to the emergence of a secondary peak in the $-uv$ co-spectra. With increasing Reynolds number, the influence of the $O(\\delta ^{+})$ motions promotes viscosity to act over increasingly longer times, thereby increasing the $y^{+}$ extent over which the mean viscous force retains leading order. Furthermore, the TI decompositions show that the $\\langle v \\omega _z \\rangle $ motions (advective transport and/or dispersion of vorticity) are the dominant mechanism in and above the log region, whereas $\\langle - w \\omega _y \\rangle $ motions (vorticity stretching and/or reorientation) are most significant below the log region. The motions associated with $\\langle - w \\omega _y \\rangle $ predominantly underlie accelerations, whereas $\\langle v \\omega _z \\rangle $ primarily contribute to decelerations. Finally, a description of the structure of wall turbulence deduced from the present analysis and our physical interpretation is presented, and is shown to be consistent with previous flow visualisation studies.

Ensuring best practice in genomics education and evaluation: reporting item standards for education and its evaluation in genomics (RISE2 Genomics)

Publisher: Elsevier BV

Date: 07-2021

DOI: 10.1038/S41436-021-01140-X

Modeling bed shear-stress fluctuations in a shallow tidal channel

Publisher: American Geophysical Union (AGU)

Date: 05-2014

DOI: 10.1002/2013JC009718

Inner-layer intensities for the flat-plate turbulent boundary layer combining a predictive wall-model with large-eddy simulations

Publisher: AIP Publishing

Date: 07-2012

DOI: 10.1063/1.4731299

Abstract: Time series velocity signals obtained from large-eddy simulations (LES) within the logarithmic region of the zero-pressure gradient turbulent boundary layer over a smooth wall are used in combination with an empirical, predictive inner-outer wall model [I. Marusic, R. Mathis, and N. Hutchins, “Predictive model for wall-bounded turbulent flow,” Science 329, 193 (2010)10.1126/science.1188765] to calculate the statistics of the fluctuating streamwise velocity in the inner region. Results, including spectra and moments up to fourth order, are compared with equivalent predictions using experimental time series, as well as with direct experimental measurements at Reynolds numbers Reτ = 7300, 13 600, and 19 000. The LES combined with the wall model are then used to extend the inner-layer predictions to Reynolds numbers Reτ = 62 000, 100 000, and 200 000 that lie within a gap in log (Reτ) space between laboratory measurements and surface-layer, atmospheric experiments. The present results support a loglike increase in the near-wall peak of the streamwise turbulence intensities with Reτ and also provide a means of extending LES results at large Reynolds numbers to the near-wall region of wall-bounded turbulent flows.

Study of the Log-Layer Structure in Wall Turbulence Over a Very Large Range of Reynolds Number

Publisher: Springer Science and Business Media LLC

Date: 24-11-2007

DOI: 10.1007/S10494-007-9116-0

Towards an improved spatial representation of a boundary layer from the attached eddy model

Publisher: American Physical Society (APS)

Date: 10-03-2020

DOI: 10.1103/PHYSREVFLUIDS.5.034601

Emergence of the four layer dynamical regime in turbulent pipe flow

Publisher: AIP Publishing

Date: 04-2012

DOI: 10.1063/1.3702897

Abstract: Direct numerical simulations of fully developed turbulent pipe flow that span the Reynolds number range 90 ≲ δ+ ≲ 1000 are used to investigate the evolution of the mean momentum field in and beyond the transitional regime. It is estimated that the four layer regime for pipe flow is nominally established for δ+ ⩾ 180, which is also close to the value found for channel flow. Primary attention is paid to the magnitude ordering and scaling behaviors of the terms in the mean momentum equation. Once the ordering underlying the existence of four distinct balance layers is attained, this ordering is sustained for all subsequent increases in Reynolds number. Comparisons indicate that pipe flow develops toward the four layer regime in a manner similar to that for channel flow, but distinct from that for the boundary layer. Small but discernible differences are observed in the mean momentum field development in pipes and channels. These are tentatively attributed to variations in the manner by which the outer region mean vorticity field develops in these two flows.

Generalized logarithmic law for high-order moments in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 19-02-2013

DOI: 10.1017/JFM.2013.61

Abstract: High-Reynolds-number data in turbulent boundary layers are analysed to examine statistical moments of streamwise velocity fluctuations ${u}^{\\prime } $ . Prior work has shown that the variance of ${u}^{\\prime } $ exhibits logarithmic behaviour with distance to the surface, within an inertial sublayer. Here we extend these observations to even-order moments. We show that the $2p$ -order moments, raised to the power $1/ p, $ also follow logarithmic behaviour according to $\\langle \\mathop{({u}^{\\prime + } ){}^{2p} \\rangle }\\nolimits ^{1/ p} = {B}_{p} - {A}_{p} \\ln (z/ \\delta )$ , where ${u}^{\\prime + } $ is the velocity fluctuation normalized by the friction velocity, $\\delta $ is an outer length scale and ${B}_{p} $ are non-universal constants. The slopes ${A}_{p} $ in the logarithmic region appear quite insensitive to Reynolds number, consistent with universal behaviour for wall-bounded flows. The slopes differ from predictions that assume Gaussian statistics, and instead are consistent with sub-Gaussian behaviour.

Spatial resolution correction for hot-wire anemometry in wall turbulence

Publisher: Springer Science and Business Media LLC

Date: 13-11-2010

DOI: 10.1007/S00348-010-1003-0

Estimating large-scale structures in wall turbulence using linear models

Publisher: Cambridge University Press (CUP)

Date: 06-03-2018

DOI: 10.1017/JFM.2018.129

Abstract: A dynamical systems approach is used to devise a linear estimation tool for channel flow at a friction Reynolds number of $Re_{\\unicode[STIX]{x1D70F}}=1000$ . The estimator uses time-resolved velocity measurements at a single wall-normal location to estimate the velocity field at other wall-normal locations (the data coming from direct numerical simulations). The estimation tool builds on the work of McKeon & Sharma ( J. Fluid Mech. , vol. 658, 2010, pp. 336–382) by using a Navier–Stokes-based linear model and treating any nonlinear terms as unknown forcings to an otherwise linear system. In this way nonlinearities are not ignored, but instead treated as an unknown model input. It is shown that, while the linear estimator qualitatively reproduces large-scale flow features, it tends to overpredict the litude of velocity fluctuations – particularly for structures that are long in the streamwise direction and thin in the spanwise direction. An alternative linear model is therefore formed in which a simple eddy viscosity is used to model the influence of the small-scale turbulent fluctuations on the large scales of interest. This modification improves the estimator performance significantly. Importantly, as well as improving the performance of the estimator, the linear model with eddy viscosity is also able to predict with reasonable accuracy the range of wavenumber pairs and the range of wall-normal heights over which the estimator will perform well.

Attached Eddies and High-Order Statistics

Publisher: Springer International Publishing

Date: 18-08-2015

DOI: 10.1007/978-3-319-20388-1_4

Reconstruction of Wall Shear-Stress Fluctuations in a Shallow Tidal River

Publisher: Springer International Publishing

Date: 18-08-2015

DOI: 10.1007/978-3-319-20388-1_22

Evidence of thek1−1

Publisher: American Physical Society (APS)

Date: 09-08-2005

DOI: 10.1103/PHYSREVLETT.95.074501

High Reynolds number effects in wall turbulence

Publisher: Elsevier BV

Date: 06-2010

DOI: 10.1016/J.IJHEATFLUIDFLOW.2010.01.005

Influence of spatial exclusion on the statistical behavior of attached eddies

Publisher: American Physical Society (APS)

Date: 17-06-2016

DOI: 10.1103/PHYSREVFLUIDS.1.022401

Inner–outer interactions in rough-wall turbulence

Publisher: Informa UK Limited

Date: 28-09-2016

DOI: 10.1080/14685248.2016.1235278

Simultaneous orthogonal-plane particle image velocimetry measurements in a turbulent boundary layer

Publisher: Cambridge University Press (CUP)

Date: 20-07-2006

DOI: 10.1017/S0022112006000292

Large-scale eddies and their role in entrainment in turbulent jets and wakes

Publisher: AIP Publishing

Date: 05-2012

DOI: 10.1063/1.4719156

Abstract: A large-scale or energy-containing eddy model of turbulent axisymmetric jets and wakes is developed, wherein eddies are randomly distributed in the azimuthal and convecting in the axial directions. The mean velocities and second order statistics obtained from the models agree well with the various available experimental data. There is an average inflow into the turbulent jet at the boundary, which is virtually non-existent for wakes. These eddy contributions are used to reconsider the entrainment process, which has to date been largely conceived as either an “engulfment” or “nibbling” process. Here we suggest that entrainment in turbulent jets be viewed as a three-part-process wherein non-turbulent fluid is “induced” and “engulfed” into the turbulent core due to large-scale eddies, which is converted into turbulent motion by the action of small-scale eddies via “nibbling.” However, in wakes there is no induced flow and the primary cause of entrainment is envisaged to be large-scale “engulfment” combined with small-scale “nibbling.”

Paper ID number EH010

Publisher: IEEE

Date: 02-2008

DOI: 10.1109/ISAF.2008.4693944

Comparison of turbulent channel and pipe flows with varying Reynolds number

Publisher: Springer Science and Business Media LLC

Date: 25-06-2011

DOI: 10.1007/S00348-011-1143-X

Obtaining accurate mean velocity measurements in high Reynolds number turbulent boundary layers using Pitot tubes

Publisher: Cambridge University Press (CUP)

Date: 09-01-2013

DOI: 10.1017/JFM.2012.538

Abstract: This article reports on one component of a larger study on measurement of the zero-pressure-gradient turbulent flat plate boundary layer, in which a detailed investigation was conducted of the suite of corrections required for mean velocity measurements performed using Pitot tubes. In particular, the corrections for velocity shear across the tube and for blockage effects which occur when the tube is in close proximity to the wall were investigated using measurements from Pitot tubes of five different diameters, in two different facilities, and at five different Reynolds numbers ranging from ${\\mathit{Re}}_{\\theta } = 11\\hspace{0.167em} 100$ to 67 000. Only small differences were found amongst commonly used corrections for velocity shear, but improvements were found for existing near-wall proximity corrections. Corrections for the nonlinear averaging of the velocity fluctuations were also investigated, and the results compared to hot-wire data taken as part of the same measurement c aign. The streamwise turbulence-intensity correction was found to be of comparable magnitude to that of the shear correction, and found to bring the hot-wire and Pitot results into closer agreement when applied to the data, along with the other corrections discussed and refined here.

Assessment of tomographic PIV in wall-bounded turbulence using direct numerical simulation data

Publisher: Springer Science and Business Media LLC

Date: 27-11-2011

DOI: 10.1007/S00348-011-1227-7

The logarithmic variance of streamwise velocity and conundrum in wall turbulence

Publisher: Cambridge University Press (CUP)

Date: 20-12-2021

DOI: 10.1017/JFM.2021.1057

Abstract: The logarithmic dependence of streamwise turbulence intensity has been observed repeatedly in recent experimental and direct numerical simulation data. However, its spectral counterpart, a well-developed $k^{-1}$ spectrum ( $k$ is the spatial wavenumber in a wall-parallel direction), has not been convincingly observed from the same data. In the present study, we revisit the spectrum-based attached eddy model of Perry and co-workers, who proposed the emergence of a $k^{-1}$ spectrum in the inviscid limit, for small but finite $z/\\delta$ and for finite Reynolds numbers ( $z$ is the wall-normal coordinate, and $\\delta$ is the outer length scale). In the upper logarithmic layer (or inertial sublayer), a reexamination reveals that the intensity of the spectrum must vary with the wall-normal location at order of $z/\\delta$ , consistent with the early observation argued with ‘incomplete similarity’. The streamwise turbulence intensity is subsequently calculated, demonstrating that the existence of a well-developed $k^{-1}$ spectrum is not a necessary condition for the approximate logarithmic wall-normal dependence of turbulence intensity – a more general condition is the existence of a premultiplied power-spectral intensity of $O(1)$ for $O(1/\\delta ) k O(1/z)$ . Furthermore, it is shown that the Townsend–Perry constant must be weakly dependent on the Reynolds number. Finally, the analysis is semi-empirically extended to the lower logarithmic layer (or mesolayer), and a near-wall correction for the turbulence intensity is subsequently proposed. All the predictions of the proposed model and the related analyses/assumptions are validated with high-fidelity experimental data (Samie et al. , J. Fluid Mech. , vol. 851, 2018, pp. 391–415).

Universality of the energy-containing structures in wall-bounded turbulence

Publisher: Cambridge University Press (CUP)

Date: 21-06-2017

DOI: 10.1017/JFM.2017.315

Abstract: The scaling behaviour of the longitudinal velocity structure functions $\\langle (\\unicode[STIX]{x1D6E5}_{r}u)^{2p}\\rangle ^{1 }$ (where $2p$ represents the order) is studied for various wall-bounded turbulent flows. It has been known that for very large Reynolds numbers within the logarithmic region, the structure functions can be described by $\\langle (\\unicode[STIX]{x1D6E5}_{r}u)^{2p}\\rangle ^{1 }/U_{\\unicode[STIX]{x1D70F}}^{2}\\approx D_{p}\\ln (r/z)+E_{p}$ (where $r$ is the longitudinal distance, $z$ the distance from the wall, $U_{\\unicode[STIX]{x1D70F}}$ the friction velocity and $D_{p}$ , $E_{p}$ are constants) in accordance with Townsend’s attached eddy hypothesis. Here we show that the ratios $D_{p}/D_{1}$ extracted from plots between structure functions – in the spirit of the extended self-similarity hypothesis – have further reaching universality for the energy containing range of scales. Specifically, we confirm that this description is universal across wall-bounded flows with different flow geometries, and also for both the longitudinal and transversal structure functions, where previously the scaling has been either difficult to discern or differences have been reported when examining the direct representation of $\\langle (\\unicode[STIX]{x1D6E5}_{r}u)^{2p}\\rangle ^{1 }$ . In addition, we present evidence of this universality at much lower Reynolds numbers, which opens up avenues to examine structure functions that are not readily available from high Reynolds number databases.

Scaling of the streamwise turbulence intensity in the context of inner-outer interactions in wall turbulence

Publisher: American Physical Society (APS)

Date: 17-10-2017

DOI: 10.1103/PHYSREVFLUIDS.2.100502

Crossing Turbulent Boundaries: Interfacial Flux in Environmental Flows

Publisher: American Chemical Society (ACS)

Date: 09-08-2011

DOI: 10.1021/ES201778S

Abstract: Advances in the visualization and prediction of turbulence are shedding new light on mass transfer in the turbulent boundary layer. These discoveries have important implications for many topics in environmental science and engineering, from the transport of earth-warming CO2 across the sea-air interface, to nutrient processing and sediment erosion in rivers, lakes, and the ocean, to pollutant removal in water and wastewater treatment systems. In this article we outline current understanding of turbulent boundary layer flows, with particular focus on coherent turbulence and its impact on mass transport across the sediment-water interface in marine and freshwater systems.

A parametric study of adverse pressure gradient turbulent boundary layers

Publisher: Elsevier BV

Date: 06-2011

DOI: 10.1016/J.IJHEATFLUIDFLOW.2011.03.004

Experimental fluid dynamics characterization of a novel micropump-mixer

Publisher: AIP Publishing

Date: 07-2020

DOI: 10.1063/5.0012240

Abstract: The application of lab-on-a-chip systems to biomedical engineering and medical biology is rapidly growing. Reciprocating micropumps show significant promise as automated bio-fluid handling systems and as active reagent-to-s le mixers. Here, we describe a thorough fluid dynamic analysis of an active micro-pump-mixer designed for applications of preclinical blood analysis and clinical diagnostics in hematology. Using high-speed flow visualization and micro-particle image velocimetry measurements, a parametric study is performed to investigate the fluid dynamics of six discrete modes of micropump operation. With this approach, we identify an actuation regime that results in optimal s le flow rates while concomitantly maximizing reagent-to-s le mixing.

Big trouble for little fish: identifying Australian freshwater fishes in imminent risk of extinction

Publisher: CSIRO Publishing

Date: 2020

DOI: 10.1071/PC19053

Abstract: Globally, freshwater fishes are declining at an alarming rate. Despite much evidence of catastrophic declines, few Australian species are listed as threatened under national legislation. We aim to help redress this by identifying the Australian freshwater fishes that are in the most immediate risk of extinction. For 22 freshwater fishes (identified as highly threatened by experts), we used structured expert elicitation to estimate the probability of extinction in the next ~20 years, and to identify key threats and priority management needs. All but one of the 22 species are small (& mm total length), 12 have been formally described only in the last decade, with seven awaiting description. Over 90% of these species were assessed to have a & % probability of extinction in the next ~20 years. Collectively, the biggest factor contributing to the likelihood of extinction of the freshwater fishes considered is that they occur in small (distributions ≤44km2), geographically isolated populations, and are threatened by a mix of processes (particularly alien fishes and climate change). Nineteen of these species are unlisted on national legislation, so legislative drivers for recovery actions are largely absent. Research has provided strong direction on how to manage ~35% of known threats to the species considered, and, of these, ~36% of threats have some management underway (although virtually none are at the stage where intervention is no longer required). Increased resourcing, management intervention and social attitudinal change is urgently needed to avert the impending extinction of Australia’s most imperilled freshwater fishes.

Spatial averaging effects on the streamwise and wall-normal velocity measurements in a wall-bounded turbulence using a cross-wire probe

Publisher: IOP Publishing

Date: 02-07-2019

DOI: 10.1088/1361-6501/AB2587

Experimental study of a turbulent boundary layer with a rough-to-smooth change in surface conditions at high Reynolds numbers

Publisher: Cambridge University Press (CUP)

Date: 27-07-2021

DOI: 10.1017/JFM.2021.577

Amplitude modulation of pressure in turbulent boundary layer

Publisher: Elsevier BV

Date: 10-2016

DOI: 10.1016/J.IJHEATFLUIDFLOW.2016.05.019

Simultaneous micro-PIV measurements and real-time control trapping in a cross-slot channel

Publisher: Springer Science and Business Media LLC

Date: 09-11-2018

DOI: 10.1007/S00348-018-2637-6

On the relationship between manipulated inter-scale phase and energy-efficient turbulent drag reduction

Publisher: Cambridge University Press (CUP)

Date: 26-09-2023

DOI: 10.1017/JFM.2023.715

A wall-shear stress predictive model

Publisher: IOP Publishing

Date: 22-12-2011

DOI: 10.1088/1742-6596/318/1/012003

The relationship between the velocity skewness and the amplitude modulation of the small scale by the large scale in turbulent boundary layers

Publisher: AIP Publishing

Date: 12-2011

DOI: 10.1063/1.3671738

Abstract: A defining feature of the inner-outer interactions in wall-bounded turbulent flows is the imprint of the outer large-scale motions on the inner small scale. Recently, Mathis et al. [“Large-scale litude modulation of the small-scale structures in turbulent boundary layers,” J. Fluid Mech. 628, 311 (2009)] quantified this imprint by applying the Hilbert transform to small-scale components of the fluctuating streamwise velocity, u. They found that the wall-normal profile of the litude modulation between the large scale and the envelope of the small scale exhibits strong resemblance to the skewness profile of u. In this study, we assess this apparent relationship and show that the Reynolds number trend in the skewness profile of u is strongly related to the litude modulation effect of the small scales by the large. This observation also leads to an alternative diagnostic for the litude modulation effect, which is one component of the skewness factor based on a scale decomposition.

Data-driven decomposition of the streamwise turbulence kinetic energy in boundary layers. Part 1. Energy spectra

Publisher: Cambridge University Press (CUP)

Date: 12-11-2019

DOI: 10.1017/JFM.2019.834

Data-driven decomposition of the streamwise turbulence kinetic energy in boundary layers. Part 2. Integrated energy and

Publisher: Cambridge University Press (CUP)

Date: 12-11-2019

DOI: 10.1017/JFM.2019.835

Evolution of the turbulent/non-turbulent interface of an axisymmetric turbulent jet

Publisher: Springer Science and Business Media LLC

Date: 2013

DOI: 10.1007/S00348-012-1449-3

Spatial averaging of streamwise and spanwise velocity measurements in wall-bounded turbulence using ν- and x-probes

Publisher: IOP Publishing

Date: 25-09-2013

DOI: 10.1088/0957-0233/24/11/115302

Spatial averaging of velocity measurements in wall-bounded turbulence: Single hot-wires

Publisher: IOP Publishing

Date: 25-09-2013

DOI: 10.1088/0957-0233/24/11/115301

Spectral-scaling-based extension to the attached eddy model of wall turbulence

Publisher: American Physical Society (APS)

Date: 16-10-2020

DOI: 10.1103/PHYSREVFLUIDS.5.104606

The coupling between inner and outer scales in a zero pressure boundary layer evaluated using a Hölder exponent framework

Publisher: IOP Publishing

Date: 19-02-2016

DOI: 10.1088/0169-5983/48/2/021405

Elastomeric microvalve geometry affects haemocompatibility

Publisher: Royal Society of Chemistry (RSC)

Date: 2018

DOI: 10.1039/C7LC01320E

Abstract: Using a battery of biological and haemodynamic testing we identify a pneumatic microvalve geometry with optimised haemocompatibility.

Coherent large-scale structures from the linearized Navier–Stokes equations

Publisher: Cambridge University Press (CUP)

Date: 20-06-2019

DOI: 10.1017/JFM.2019.391

Abstract: The wall-normal extent of the large-scale structures modelled by the linearized Navier–Stokes equations subject to stochastic forcing is directly compared to direct numerical simulation (DNS) data. A turbulent channel flow at a friction Reynolds number of $Re_{\\unicode[STIX]{x1D70F}}=2000$ is considered. We use the two-dimensional (2-D) linear coherence spectrum (LCS) to perform the comparison over a wide range of energy-carrying streamwise and spanwise length scales. The study of the 2-D LCS from DNS indicates the presence of large-scale structures that are coherent over large wall-normal distances and that are self-similar. We find that, with the addition of an eddy viscosity profile, these features of the large-scale structures are captured by the linearized equations, except in the region close to the wall. To further study this coherence, a coherence-based estimation technique, spectral linear stochastic estimation, is used to build linear estimators from the linearized Navier–Stokes equations. The estimator uses the instantaneous streamwise velocity field or the 2-D streamwise energy spectrum at one wall-normal location (obtained from DNS) to predict the same quantity at a different wall-normal location. We find that the addition of an eddy viscosity profile significantly improves the estimation.

Modelling the downstream development of a turbulent boundary layer following a step change of roughness

Publisher: Cambridge University Press (CUP)

Date: 23-09-2022

DOI: 10.1017/JFM.2022.731

Abstract: In this study, we develop an analytical model to predict the turbulent boundary layer downstream of a step-change in the surface roughness where upstream flow conditions are given. We first revisit the classical model of Elliott ( Trans. Am. Geophys. Union , vol. 39, 1958, pp. 1048–1054), who modelled the velocity distribution within and above the internal layer with a simple piecewise logarithmic profile, and evolved the velocity profile using the streamwise momentum equation. Elliott's model was originally developed for an atmospheric surface layer, and to make the model applicable to a spatially developing turbulent boundary layer with finite thickness, we propose a number of more physical refinements, including adding a wake function to the velocity profile, considering the growth of the entire boundary layer in the streamwise direction, and using a more realistic shear stress profile in the momentum equation. In particular, we implement the blending model (Li et al. , J. Fluid Mech. , vol. 923, 2021, p. A18) to account for the deviation of the mean flow within the internal layer from a canonical velocity profile based on the local wall condition. These refinements lead to improved agreement between the prediction and the measurement, especially in the vicinity of the rough-to-smooth change.

Coherent structures in the linearized impulse response of turbulent channel flow

Publisher: Cambridge University Press (CUP)

Date: 30-01-2019

DOI: 10.1017/JFM.2019.15

Abstract: We study the evolution of velocity fluctuations due to an isolated spatio-temporal impulse using the linearized Navier–Stokes equations. The impulse is introduced as an external body force in incompressible channel flow at $Re_{\\unicode[STIX]{x1D70F}}=10\\,000$ . Velocity fluctuations are defined about the turbulent mean velocity profile. A turbulent eddy viscosity is added to the equations to fix the mean velocity as an exact solution, which also serves to model the dissipative effects of the background turbulence on large-scale fluctuations. An impulsive body force produces flow fields that evolve into coherent structures containing long streamwise velocity streaks that are flanked by quasi-streamwise vortices some of these impulses produce hairpin vortices. As these vortex–streak structures evolve, they grow in size to be nominally self-similar geometrically with an aspect ratio (streamwise to wall-normal) of approximately 10, while their kinetic energy density decays monotonically. The topology of the vortex–streak structures is not sensitive to the location of the impulse, but is dependent on the direction of the impulsive body force. All of these vortex–streak structures are attached to the wall, and their Reynolds stresses collapse when scaled by distance from the wall, consistent with Townsend’s attached-eddy hypothesis.

13th International Symposium on Particle Image Velocimetry (ISPIV 2019)

Publisher: IOP Publishing

Date: 04-2021

DOI: 10.1088/1361-6501/ABBE3C

An energy-efficient pathway to turbulent drag reduction

Publisher: Springer Science and Business Media LLC

Date: 04-10-2021

DOI: 10.1038/S41467-021-26128-8

Abstract: Simulations and experiments at low Reynolds numbers have suggested that skin-friction drag generated by turbulent fluid flow over a surface can be decreased by oscillatory motion in the surface, with the amount of drag reduction predicted to decline with increasing Reynolds number. Here, we report direct measurements of substantial drag reduction achieved by using spanwise surface oscillations at high friction Reynolds numbers ( $${{{\\mathrm{Re}}}_{\\tau }}$$ Re τ ) up to 12,800. The drag reduction occurs via two distinct physical pathways. The first pathway, as studied previously, involves actuating the surface at frequencies comparable to those of the small-scale eddies that dominate turbulence near the surface. We show that this strategy leads to drag reduction levels up to 25% at $${{{{{{{{\\mathrm{Re}}}}}}}}}_{\\tau }$$ Re τ = 6,000, but with a power cost that exceeds any drag-reduction savings. The second pathway is new, and it involves actuation at frequencies comparable to those of the large-scale eddies farther from the surface. This alternate pathway produces drag reduction of 13% at $${{{{{{{{\\mathrm{Re}}}}}}}}}_{\\tau }$$ Re τ = 12,800. It requires significantly less power and the drag reduction grows with Reynolds number, thereby opening up potential new avenues for reducing fuel consumption by transport vehicles and increasing power generation by wind turbines.

Scaling of second- and higher-order structure functions in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 30-03-2015

DOI: 10.1017/JFM.2015.122

Abstract: The statistical properties of wall turbulence in the logarithmic region are investigated using structure functions of the streamwise velocity. To this end, datasets that span several orders of magnitude of Reynolds numbers are used, up to $Re_{{\\it\\tau}}=O(10^{6})$ , providing uniquely large scale separations for scrutinising previously proposed scaling laws. For the second-order structure functions strong support is found simultaneously for power-law scalings in the Kolmogorov inertial subrange and for logarithmic scaling at larger scales within the inertial range ( $z r\\ll {\\it\\delta}$ , where $z$ is the distance from the wall, $r$ the scale, and ${\\it\\delta}$ the boundary layer thickness). The observed scalings are shown to agree between the datasets, which include both temporal and spatial velocity signals and span from laboratory to atmospheric flows, showing a degree of universality in the results presented. An examination of higher even-order structure functions also shows support for logarithmic scaling behaviour for $z r\\ll {\\it\\delta}$ , provided that the Reynolds number is sufficiently high. These findings are interpreted by generalising the work of Meneveau & Marusic ( J. Fluid Mech. , vol. 719, 2013) and introducing bridging relations between higher-order moments of velocity fluctuations and structure functions. Further, a physical model based on the attached-eddy hypothesis is utilised to derive various properties of the structure functions for the energy-containing scales of the logarithmic region. The descriptions derived from the model are shown to be supported by the experimental data.

Pressure power spectrum in high-Reynolds number wall-bounded flows

Publisher: Elsevier BV

Date: 08-2020

DOI: 10.1016/J.IJHEATFLUIDFLOW.2020.108620

Wall-drag measurements of smooth- and rough-wall turbulent boundary layers using a floating element

Publisher: Springer Science and Business Media LLC

Date: 05-2016

DOI: 10.1007/S00348-016-2168-Y

Leonardo da Vinci and Fluid Mechanics

Publisher: Annual Reviews

Date: 05-01-2021

DOI: 10.1146/ANNUREV-FLUID-022620-122816

Abstract: This review focuses on Leonardo da Vinci's work and thought related to fluid mechanics as it is presented in a lifetime of notebooks, letters, and artwork. It shows how Leonardo's remaining works offer a complicated picture of unfinished, scattered, and frequently revisited hypotheses and conclusions. It argues that experimentation formed an important mechanism for Leonardo's thought about natural fluid flows, which was an innovation to the scientific thinking of his day, but which did not always lead him to the conclusions of modern fluid mechanics. It highlights the multiple and ambiguous meanings of turbulence in his works. It examines his thinking suggestive of modern concepts such as the no-slip condition, hydraulic jump, cardiovascular vortices, conservation of volume, and the distinctive path of ascending bubbles we now term Leonardo's paradox, among others. It demonstrates how Leonardo thought through analogies, building-block flow patterns, and synthesis, leading both to successes—especially in the management of water—and to failures, perhaps most obviously in his pursuit of human flight.

Prograde vortices, internal shear layers and the Taylor microscale in high-Reynolds-number turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 16-06-2021

DOI: 10.1017/JFM.2021.478

High–Reynolds Number Wall Turbulence

Publisher: Annual Reviews

Date: 21-01-2011

DOI: 10.1146/ANNUREV-FLUID-122109-160753

Abstract: We review wall-bounded turbulent flows, particularly high–Reynolds number, zero–pressure gradient boundary layers, and fully developed pipe and channel flows. It is apparent that the approach to an asymptotically high–Reynolds number state is slow, but at a sufficiently high Reynolds number the log law remains a fundamental part of the mean flow description. With regard to the coherent motions, very-large-scale motions or superstructures exist at all Reynolds numbers, but they become increasingly important with Reynolds number in terms of their energy content and their interaction with the smaller scales near the wall. There is accumulating evidence that certain features are flow specific, such as the constants in the log law and the behavior of the very large scales and their interaction with the large scales (consisting of vortex packets). Moreover, the refined attached-eddy hypothesis continues to provide an important theoretical framework for the structure of wall-bounded turbulent flows.

Dual-plane PIV technique to determine the complete velocity gradient tensor in a turbulent boundary layer

Publisher: Springer Science and Business Media LLC

Date: 15-07-2005

DOI: 10.1007/S00348-005-1019-Z

Comparison of turbulent boundary layers over smooth and rough surfaces up to high Reynolds numbers

Publisher: Cambridge University Press (CUP)

Date: 14-04-2016

DOI: 10.1017/JFM.2016.196

Abstract: Turbulent boundary layer measurements above a smooth wall and sandpaper roughness are presented across a wide range of friction Reynolds numbers, ${\\it\\delta}_{99}^{+}$ , and equivalent sand grain roughness Reynolds numbers, $k_{s}^{+}$ (smooth wall: $2020\\leqslant {\\it\\delta}_{99}^{+}\\leqslant 21\\,430$ , rough wall: $2890\\leqslant {\\it\\delta}_{99}^{+}\\leqslant 29\\,900$ $22\\leqslant k_{s}^{+}\\leqslant 155$ and $28\\leqslant {\\it\\delta}_{99}^{+}/k_{s}^{+}\\leqslant 199$ ). For the rough-wall measurements, the mean wall shear stress is determined using a floating element drag balance. All smooth- and rough-wall data exhibit, over an inertial sublayer, regions of logarithmic dependence in the mean velocity and streamwise velocity variance. These logarithmic slopes are apparently the same between smooth and rough walls, indicating similar dynamics are present in this region. The streamwise mean velocity defect and skewness profiles each show convincing collapse in the outer region of the flow, suggesting that Townsend’s ( The Structure of Turbulent Shear Flow , vol. 1, 1956, Cambridge University Press.) wall-similarity hypothesis is a good approximation for these statistics even at these finite friction Reynolds numbers. Outer-layer collapse is also observed in the rough-wall streamwise velocity variance, but only for flows with ${\\it\\delta}_{99}^{+}\\gtrsim 14\\,000$ . At Reynolds numbers lower than this, profile invariance is only apparent when the flow is fully rough. In transitionally rough flows at low ${\\it\\delta}_{99}^{+}$ , the outer region of the inner-normalised streamwise velocity variance indicates a dependence on $k_{s}^{+}$ for the present rough surface.

Structure Inclination Angles in the Convective Atmospheric Surface Layer

Publisher: Springer Science and Business Media LLC

Date: 04-11-2012

DOI: 10.1007/S10546-012-9777-7

Evolution and structure of sink-flow turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 10-02-2001

DOI: 10.1017/S0022112000002597

Abstract: An experimental and theoretical investigation of turbulent boundary layers developing in a sink-flow pressure gradient was undertaken. Three flow cases were studied, corresponding to different acceleration strengths. Mean-flow measurements were taken for all three cases, while Reynolds stresses and spectra measurements were made for two of the flow cases. In this study attention was focused on the evolution of the layers to an equilibrium turbulent state. All the layers were found to attain a state very close to precise equilibrium. This gave equilibrium sink flow data at higher Reynolds numbers than in previous experiments. The mean velocity profiles were found to collapse onto the conventional logarithmic law of the wall. However, for profiles measured with the Pitot tube, a slight ‘kick-up’ from the logarithmic law was observed near the buffer region, whereas the mean velocity profiles measured with a normal hot wire did not exhibit this deviation from the logarithmic law. As the layers approached equilibrium, the mean velocity profiles were found to approach the pure wall profile and for the highest level of acceleration Π was very close to zero, where Π is the Coles wake factor. This supports the proposition of Coles (1957), that the equilibrium sink flow corresponds to pure wall flow. Particular interest was also given to the evolutionary stages of the boundary layers, in order to test and further develop the closure hypothesis of Perry, Marusic & Li (1994). Improved quantitative agreement with the experimental results was found after slight modification of their original closure equation.

The turbulent/non-turbulent interface and entrainment in a boundary layer

Publisher: Cambridge University Press (CUP)

Date: 21-02-2014

DOI: 10.1017/JFM.2013.641

Study of the near-wall-turbulent region of the high-Reynolds-number boundary layer using an atmospheric flow

Publisher: Cambridge University Press (CUP)

Date: 02-2006

DOI: 10.1017/S0022112005007780

Comparison of large-scale amplitude modulation in turbulent boundary layers, pipes, and channel flows

Publisher: AIP Publishing

Date: 11-2009

DOI: 10.1063/1.3267726

Abstract: Recent investigations by Monty et al. [J. Fluid Mech. 632, 431 (2009)] showed that important modal differences exist between channels ipes and boundary layers, mainly in the largest energetic scales. In addition, Mathis et al. [J. Fluid Mech. 628, 311 (2009)] recently reported and quantified a nonlinear scale interaction in zero-pressure gradient turbulent boundary layers, whereby the large-scale motion litude modulates the small-scale motions. In this study, a comparison of this modulation effect of the streamwise velocity component is undertaken for all three flows for matched Reynolds number and measurement conditions. Despite the different large-scale phenomena in these internal and external wall-bounded flows, the results show that their litude modulation influence remains invariant in the inner region with some differences appearing in the outer region.

Large coherence of spanwise velocity in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 21-05-2018

DOI: 10.1017/JFM.2018.320

Abstract: The spatial signature of spanwise velocity coherence in turbulent boundary layers has been studied using a series of unique large-field-of-view multicamera particle image velocimetry experiments, which were configured to capture streamwise/spanwise slices of the boundary layer in both the logarithmic and the wake regions. The friction Reynolds number of $Re_{\\unicode[STIX]{x1D70F}}\\approx 2600$ was chosen to nominally match the simulation of Sillero et al. ( Phys. Fluids , vol. 26 (10), 2014, 105109), who had previously reported oblique features of the spanwise coherence at the top edge of the boundary layer based on the sign of the spanwise velocity, and here we find consistent observations from experiments. In this work, we show that these oblique features in the spanwise coherence relate to the intermittent turbulent bulges at the edge of the layer, and thus the geometry of the turbulent/non-turbulent interface, with the clear appearance of two counter-oriented oblique features. Further, these features are shown to be also present in the logarithmic region once the velocity fields are deconstructed based on the sign of both the spanwise and the streamwise velocity, suggesting that the often-reported meandering of the streamwise-velocity coherence in the logarithmic region is associated with a more obvious diagonal pattern in the spanwise velocity coherence. Moreover, even though a purely visual inspection of the obliqueness in the spanwise coherence may suggest that it extends over a very large spatial extent (beyond many boundary layer thicknesses), through a conditional analysis, we show that this coherence is limited to distances nominally less than two boundary layer thicknesses. Interpretation of these findings is aided by employing synthetic velocity fields of a boundary layer constructed using the attached eddy model, where the range of eddy sizes can be prescribed. Comparisons between the model, which employs an array of self-similar packet-like eddies that are randomly distributed over the plane of the wall, and the experimental velocity fields reveal a good degree of agreement, with both exhibiting oblique features in the spanwise coherence over comparable spatial extents. These findings suggest that the oblique features in the spanwise coherence are likely to be associated with similar structures to those used in the model, providing one possible underpinning structural composition that leads to this behaviour. Further, these features appear to be limited in spatial extent to only the order of the large-scale motions in the flow.

Spring constant calibration of atomic force microscope cantilevers of arbitrary shape

Publisher: AIP Publishing

Date: 10-2012

DOI: 10.1063/1.4757398

Abstract: The spring constant of an atomic force microscope cantilever is often needed for quantitative measurements. The calibration method of Sader et al. [Rev. Sci. Instrum. 70, 3967 (1999)]10.1063/1.1150021 for a rectangular cantilever requires measurement of the resonant frequency and quality factor in fluid (typically air), and knowledge of its plan view dimensions. This intrinsically uses the hydrodynamic function for a cantilever of rectangular plan view geometry. Here, we present hydrodynamic functions for a series of irregular and non-rectangular atomic force microscope cantilevers that are commonly used in practice. Cantilever geometries of arrow shape, small aspect ratio rectangular, quasi-rectangular, irregular rectangular, non-ideal trapezoidal cross sections, and V-shape are all studied. This enables the spring constants of all these cantilevers to be accurately and routinely determined through measurement of their resonant frequency and quality factor in fluid (such as air). An approximate formulation of the hydrodynamic function for microcantilevers of arbitrary geometry is also proposed. Implementation of the method and its performance in the presence of uncertainties and non-idealities is discussed, together with conversion factors for the static and dynamic spring constants of these cantilevers. These results are expected to be of particular value to the design and application of micro- and nanomechanical systems in general.

A microfluidic method to investigate platelet mechanotransduction under extensional strain

Publisher: Elsevier BV

Date: 2023

DOI: 10.1016/J.RPTH.2023.100037

On the mixing length eddies and logarithmic mean velocity profile in wall turbulence

Publisher: Cambridge University Press (CUP)

Date: 21-01-2020

DOI: 10.1017/JFM.2020.23

Examining the inertial subrange with nanoscale cross-wire measurements of turbulent pipe flow at high Reynolds number near the centreline

Publisher: Cambridge University Press (CUP)

Date: 26-05-2021

DOI: 10.1017/JFM.2021.382

Applicability of Taylor’s hypothesis in rough- and smooth-wall boundary layers

Publisher: Cambridge University Press (CUP)

Date: 28-12-2016

DOI: 10.1017/JFM.2016.832

Abstract: The spatial structure of smooth- and rough-wall boundary layers is examined spectrally at approximately matched friction Reynolds number ( $\\unicode[STIX]{x1D6FF}^{+}\\approx 12\\,000$ ). For each wall condition, temporal and true spatial descriptions of the same flow are available from hot-wire anemometry and high-spatial-range particle image velocimetry, respectively. The results show that over the resolved flow domain, which is limited to a streamwise length of twice the boundary layer thickness, true spatial spectra of smooth-wall streamwise and wall-normal velocity fluctuations agree, to within experimental uncertainty, with those obtained from time series using Taylor’s frozen turbulence hypothesis ( Proc. R. Soc. Lond. A, vol. 164, 1938, pp. 476–490). The same applies for the streamwise velocity spectra on rough walls. For the wall-normal velocity spectra, however, clear differences are observed between the true spatial and temporally convected spectra. For the rough-wall spectra, a correction is derived to enable accurate prediction of wall-normal velocity length scales from measurements of their time scales, and the implications of this correction are considered. Potential violations to Taylor’s hypothesis in flows above perturbed walls may help to explain conflicting conclusions in the literature regarding the effect of near-wall modifications on outer-region flow. In this regard, all true spatial and corrected spectra presented here indicate structural similarity in the outer region of smooth- and rough-wall flows, providing evidence for Townsend’s wall-similarity hypothesis ( The Structure of Turbulent Shear Flow , vol. 1, 1956).

Effects of Pressure Gradient on Higher Order Statistics in Turbulent Boundary Layers

Publisher: Begellhouse

Date: 2012

DOI: 10.1615/ICHMT.2012.PROCSEVINTSYMPTURBHEATTRANSFPAL.2170

Attached Eddy Model of Wall Turbulence

Publisher: Annual Reviews

Date: 05-01-2019

DOI: 10.1146/ANNUREV-FLUID-010518-040427

Abstract: Modeling wall turbulence remains a major challenge, as a sufficient physical understanding of these flows is still lacking. In an effort to move toward a physics-based model, A.A. Townsend introduced the hypothesis that the dominant energy-containing motions in wall turbulence are due to large eddies attached to the wall. From this simple hypothesis, the attached eddy model evolved, which has proven to be highly effective in predicting velocity statistics and providing a framework for interpreting the energy-containing flow physics at high Reynolds numbers. This review summarizes the hypothesis itself and the modeling attempts made thereafter, with a focus on the validity of the model's assumptions and its limitations. Here, we review studies on this topic, which have markedly increased in recent years, highlighting refinements, extensions, and promising future directions for attached eddy modeling.

Reynolds Number Dependence of the Amplitude Modulated Near-Wall Cycle

Publisher: Springer Netherlands

Date: 2011

DOI: 10.1007/978-90-481-9603-6_11

Multiscale analysis of fluxes at the turbulent/non-turbulent interface in high Reynolds number boundary layers

Publisher: AIP Publishing

Date: 2014

DOI: 10.1063/1.4861066

Abstract: Analysis of fluxes across the turbulent/non-turbulent interface (TNTI) of turbulent boundary layers is performed using data from two-dimensional particle image velocimetry (PIV) obtained at high Reynolds numbers. The interface is identified with an iso-surface of kinetic energy, and the rate of change of total kinetic energy (K) inside a control volume with the TNTI as a bounding surface is investigated. Features of the growth of the turbulent region into the non-turbulent region by molecular diffusion of K, viscous nibbling, are examined in detail, focussing on correlations between interface orientation, viscous stress tensor elements, and local fluid velocity. At the level of the ensemble (Reynolds) averaged Navier-Stokes equations (RANS), the total kinetic energy K is shown to evolve predominantly due to the turbulent advective fluxes occurring through an average surface which differs considerably from the local, corrugated, sharp interface. The analysis is generalized to a hierarchy of length-scales by spatial filtering of the data as used commonly in Large-Eddy-Simulation (LES) analysis. For the same overall entrainment rate of total kinetic energy, the theoretical analysis shows that the sum of resolved viscous and subgrid-scale advective flux must be independent of scale. Within the experimental limitations of the PIV data, the results agree with these trends, namely that as the filter scale increases, the viscous resolved fluxes decrease while the subgrid-scale advective fluxes increase and tend towards the RANS values at large filter sizes. However, a definitive conclusion can only be made with fully resolved three-dimensional data, over and beyond the large dynamic spatial range presented here. The qualitative trends from the measurement results provide evidence that large-scale transport due to the energy-containing eddies determines the overall rate of entrainment, while viscous effects at the smallest scales provide the physical mechanism ultimately responsible for entrainment. Data spanning over a decade in Reynolds number suggest that the fluxes (or the entrainment velocity) scale with the friction velocity (or equivalently the local turbulent fluctuating velocity), whereas Taylor microscale and boundary-layer thickness are the appropriate length scales at small and large filter sizes, respectively.

Streamwise turbulence intensity formulation for flat-plate boundary layers

Publisher: AIP Publishing

Date: 02-07-2003

DOI: 10.1063/1.1589014

Abstract: A similarity formulation is proposed to describe the streamwise turbulence intensity across the entire smooth-wall zero-pressure-gradient turbulent boundary layer. The formulation is an extension of the Marusic, Uddin, and Perry [Phys. Fluids 9, 3718 (1997)] formulation that was restricted to the outer region of the boundary layer, including the logarithmic region. The new formulation is found to agree very well with experimental data over a large range of Reynolds numbers varying from laboratory to atmospheric flows. The formulation is founded on physical arguments based on the attached eddy hypothesis, and suggests that the boundary layer changes significantly with Reynolds number, with an outer flow influence felt all the way down to the viscous sublayer. The formulation may also be used to explain why the empirical mixed scaling of DeGraaff and Eaton [J. Fluid Mech. 422, 319 (2000)] appears to work.

Three-dimensional conditional structure of a high-Reynolds-number turbulent boundary layer

Publisher: Cambridge University Press (CUP)

Date: 22-02-2011

DOI: 10.1017/S0022112010006245

Abstract: An array of surface hot-film shear-stress sensors together with a traversing hot-wire probe is used to identify the conditional structure associated with a large-scale skin-friction event in a high-Reynolds-number turbulent boundary layer. It is found that the large-scale skin-friction events convect at a velocity that is much faster than the local mean in the near-wall region (the convection velocity for large-scale skin-friction fluctuations is found to be close to the local mean at the midpoint of the logarithmic region). Instantaneous shear-stress data indicate the presence of large-scale structures at the wall that are comparable in scale and arrangement to the superstructure events that have been previously observed to populate the logarithmic regions of turbulent boundary layers. Conditional averages of streamwise velocity computed based on a low skin-friction footprint at the wall offer a wider three-dimensional view of the average superstructure event. These events consist of highly elongated forward-leaning low-speed structures, flanked on either side by high-speed events of similar general form. An analysis of small-scale energy associated with these large-scale events reveals that the small-scale velocity fluctuations are attenuated near the wall and upstream of a low skin-friction event, while downstream and above the low skin-friction event, the fluctuations are significantly lified. In general, it is observed that the attenuation and lification of the small-scale energy seems to approximately align with large-scale regions of streamwise acceleration and deceleration, respectively. Further conditional averaging based on streamwise skin-friction gradients confirms this observation. A conditioning scheme to detect the presence of meandering large-scale structures is also proposed. The large-scale meandering events are shown to be a possible source of the strong streamwise velocity gradients, and as such play a significant role in modulating the small-scale motions.

Empirical mode decomposition and Hilbert transforms for analysis of oil-film interferograms

Publisher: IOP Publishing

Date: 25-08-2010

DOI: 10.1088/0957-0233/21/10/105405

Introduction to Topical Issue on Extreme Flows

Publisher: Springer Science and Business Media LLC

Date: 11-12-2015

DOI: 10.1007/S00348-015-2094-4

On the maximum drag reduction due to added polymers in Poiseuille flow

Publisher: Cambridge University Press (CUP)

Date: 27-07-2010

DOI: 10.1017/S0022112010003083

Abstract: The addition of elastic polymers to turbulent liquids is known to produce significant drag reduction. In this study, we prove that the drag in pipe and channel flows of an unforced laminar fluid constitutes a lower bound for the drag of a fluid containing dilute elastic polymers. Further, the addition of elastic polymers to laminar fluids invariably increases drag. This proof does not rely on the adoption of a particular constitutive equation for the polymer force, and would also be applicable to other similar methods of drag reduction, which are also achieved by the addition of certain particles to a flow. Ex les of such methods include the addition of surfactants to a flowing liquid and the presence of sand particles in sandstorms and water droplets in cyclones.

Experimental investigation of vortex properties in a turbulent boundary layer

Publisher: AIP Publishing

Date: 05-2006

DOI: 10.1063/1.2196089

Abstract: Dual-plane particle image velocimetry experiments were performed in a turbulent boundary layer with Reτ=1160 to obtain all components of the velocity gradient tensor. Wall-normal locations in the logarithmic and wake region were examined. The availability of the complete gradient tensor facilitates improved identification of vortex cores and determination of their orientation and size. Inclination angles of vortex cores were computed using statistical tools such as two-point correlations and joint probability density functions. Also, a vortex identification technique was employed to identify in idual cores and to compute inclination angles directly from instantaneous fields. The results reveal broad distributions of inclination angles at both locations. The results are consistent with the presence of many hairpin vortices which are most frequently inclined downstream at an angle of 45∘ with the wall. According to the probability density functions, a relatively small percentage of cores are inclined upstream. The number density of forward leaning cores decreases from the logarithmic to the outer region while the number density of backward-leaning cores remains relatively constant. These trends, together with the correlation statistics, suggest that the backward-leaning cores are part of smaller, weaker structures that have been distorted and convected by larger, predominantly forward-leaning eddies associated with the local shear.

Flow development in rough-bed open channels

Publisher: Informa UK Limited

Date: 20-12-2023

DOI: 10.1080/00221686.2022.2132311

Distance-from-the-wall scaling of turbulent motions in wall-bounded flows

Publisher: AIP Publishing

Date: 02-2017

DOI: 10.1063/1.4974354

Abstract: An assessment of self-similarity in the inertial sublayer is presented by considering the wall-normal velocity, in addition to the streamwise velocity component. The novelty of the current work lies in the inclusion of the second velocity component, made possible by carefully conducted subminiature ×-probe experiments to minimise the errors in measuring the wall-normal velocity. We show that not all turbulent stress quantities approach the self-similar asymptotic state at an equal rate as the Reynolds number is increased, with the Reynolds shear stress approaching faster than the streamwise normal stress. These trends are explained by the contributions from attached eddies. Furthermore, the Reynolds shear stress cospectra, through its scaling with the distance from the wall, are used to assess the wall-normal limits where self-similarity applies within the wall-bounded flow. The results are found to be consistent with the recent prediction from the work of Wei et al. [“Properties of the mean momentum balance in turbulent boundary layer, pipe and channel flows,” J. Fluid Mech. 522, 303–327 (2005)], Klewicki [“Reynolds number dependence, scaling, and dynamics of turbulent boundary layers,” J. Fluids Eng. 132, 094001 (2010)], and others that the self-similar region starts and ends at z+∼O(δ+) and O(δ+), respectively. Below the self-similar region, empirical evidence suggests that eddies responsible for turbulent stresses begin to exhibit distance-from-the-wall scaling at a fixed z+ location however, they are distorted by viscous forces, which remain a leading order contribution in the mean momentum balance in the region z+≲O(δ+), and thus result in a departure from self-similarity.

Predictive Model for Wall-Bounded Turbulent Flow

Publisher: American Association for the Advancement of Science (AAAS)

Date: 09-07-2010

DOI: 10.1126/SCIENCE.1188765

Abstract: When needing to mix two fluids rapidly, turbulent flow can be beneficial. However, in most cases, the churning and tumbling motions of a fluid during turbulent flow reduce the efficiency of a device or process. When fluid flows past a solid object, the bulk of the turbulent motion is concentrated at the surface boundary, but it is unclear to what extent these inner motions are influenced by flow far from the boundary. Marusic et al. (p. 193 see the Perspective by Adrian ) demonstrate a nonlinear connection between inner-layer motions and the large-scale outer-layer motions in wind tunnel experiments. A simple model was able to describe the relationship mathematically while accurately mapping the experimental data.

On the logarithmic region in wall turbulence

Publisher: Cambridge University Press (CUP)

Date: 28-01-2013

DOI: 10.1017/JFM.2012.511

Abstract: Considerable discussion over the past few years has been devoted to the question of whether the logarithmic region in wall turbulence is indeed universal. Here, we analyse recent experimental data in the Reynolds number range of nominally $2\\times 1{0}^{4} \\lt {\\mathit{Re}}_{\\tau } \\lt 6\\times 1{0}^{5} $ for boundary layers, pipe flow and the atmospheric surface layer, and show that, within experimental uncertainty, the data support the existence of a universal logarithmic region. The results support the theory of Townsend ( The Structure of Turbulent Shear Flow , Vol. 2, 1976) where, in the interior part of the inertial region, both the mean velocities and streamwise turbulence intensities follow logarithmic functions of distance from the wall.

Glochidia ecology in wild fish populations and laboratory determination of competent host fishes for an endemic freshwater mussel of south-western Australia

Publisher: CSIRO Publishing

Date: 2012

DOI: 10.1071/ZO12022

Abstract: Glochidia (parasitic larvae) of freshwater mussels generally require a fish as a host. Westralunio carteri Iredale, 1934 (Bivalvia : Hyriidae), the only freshwater mussel found in south-western Australia, was listed as Vulnerable, but recently changed to Least Concern (International Union for the Conservation of Nature). Glochidia were found on four alien and seven native species of fish from 18 sites in the South West Coast Drainage Division. On alien fishes, prevalence of glochidia ranged from 0.0 to 41.0% and mean intensity (number of glochidia per infested fish) from 1.0 to 6.0, while on native fishes prevalence was 9.2–90.5% and intensity was 2.3–7.1. Glochidia infestation was greatest on benthic fishes, which may be a consequence of greater encounter rates, but other factors, such as host size, probably also influence glochidia prevalence and intensity. Glochidia were generally restricted to fins of infested fish, and were rarely on gills or the body surface. In the laboratory, four native and one alien fish species were found to be competent hosts for their ability to produce juvenile W. carteri, but two alien fish species were not. The inability of some alien fishes to produce juvenile W. carteri could potentially reduce recruitment success in areas dominated by alien fishes.

Estimating wall-shear-stress fluctuations given an outer region input

Publisher: Cambridge University Press (CUP)

Date: 09-01-2013

DOI: 10.1017/JFM.2012.508

Abstract: A model for the instantaneous wall-shear-stress distribution is presented for zero-pressure-gradient turbulent boundary layers. The model, based on empirical and theoretical considerations, is able to reconstruct a statistically representative fluctuating wall-shear-stress time-series, ${ \\tau }_{w}^{\\ensuremath{\\prime} } (t)$ , using only the low-frequency content of the streamwise velocity measured in the logarithmic region, away from the wall. Results, including spectra and second-order moments, show that the model is capable of successfully capturing Reynolds number trends as observed in other studies.

Australians’ perspectives on support around use of personal genomic testing: Findings from the Genioz study

Publisher: Elsevier BV

Date: 06-0005

DOI: 10.1016/J.EJMG.2018.11.002

Abstract: Personal genomic testing using direct-to-consumer and consumer-directed models, with or without involvement of healthcare providers, is increasing internationally, including in Australia. This study forms a sub-set of the Genioz study - Genomics: National Insights of Australians. We aimed to explore Australians' experiences with these types of tests, especially online DNA tests, and their views regarding whom they would seek support from around understanding test results. The study used a mixed methods approach, employing an exploratory quantitative online survey and follow-up qualitative semi-structured interviews. Between May 2016 and May 2017, 2841 Australians responded to the survey. Interviews were conducted with 63 purposively s led respondents, including 45 who had a genetic test and 18 who had not. Of 571 respondents who had any type of genetic test, 322 had a personal genomic test using criteria defined by the researchers. Testing for ancestry/genealogy was the most common, reported by 267 participants, reflecting the increased advertising of these tests in Australia. Some respondents described downloading their raw data for further interpretation through third party websites for genealogical as well as health related information. Carrier testing, testing for serious and preventable conditions and nutrition and/or wellness were the most common health related tests reported by respondents. Participants generally preferred to seek support from general practitioners (GPs), medical specialists with relevant expertise and independent genetics specialists, although another important preference for non-health information was online forums and networks. There was less preference for seeking support from employees associated with the testing companies. Generally, of those who had a health related PGT, the most common actions were seeking medical advice or doing nothing with the information, while more of those who had a personal genomic test for nutrition and/or wellness sought advice from complementary/alternative health practitioners (eg naturopaths) and integrative GPs, and 60% reported they had changed their diet. As awareness of personal genomic testing increases, publicly funded clinical genetics services may be less inclined to discuss results from personal genomic testing. Genetic counsellors could play an important role in providing this support, both pre-test and post-test, through opportunities for private practice but independent from testing companies.

A direct comparison of pulsatile and non-pulsatile rough-wall turbulent pipe flow

Publisher: Cambridge University Press (CUP)

Date: 20-05-2020

DOI: 10.1017/JFM.2020.337

Transition to ultimate Rayleigh–Bénard turbulence revealed through extended self-similarity scaling analysis of the temperature structure functions

Publisher: Cambridge University Press (CUP)

Date: 30-07-2018

DOI: 10.1017/JFM.2018.561

Abstract: In turbulent Rayleigh–Bénard (RB) convection, a transition to the so-called ultimate regime, in which the boundary layers (BL) are of turbulent type, has been postulated. Indeed, at very large Rayleigh number $Ra\\approx 10^{13}{-}10^{14}$ a transition in the scaling of the global Nusselt number $Nu$ (the dimensionless heat transfer) and the Reynolds number with $Ra$ has been observed in experiments and very recently in direct numerical simulations (DNS) of two-dimensional (2D) RB convection. In this paper, we analyse the local scaling properties of the lateral temperature structure functions in the BLs of this simulation of 2D RB convection, employing extended self-similarity (ESS) (i.e., plotting the structure functions against each other, rather than only against the scale) in the spirit of the attached-eddy hypothesis, as we have recently introduced for velocity structure functions in wall turbulence (Krug et al. , J. Fluid Mech. , vol. 830, 2017, pp. 797–819). We find no ESS scaling at $Ra$ below the transition and in the near-wall region. However, beyond the transition and for large enough wall distance $z^{+} $ , we find clear ESS behaviour, as expected for a scalar in a turbulent boundary layer. In striking correspondence to the $Nu$ scaling, the ESS scaling region is negligible at $Ra=10^{11}$ and well developed at $Ra=10^{14}$ , thus providing strong evidence that the observed transition in the global Nusselt number at $Ra\\approx 10^{13}$ indeed is the transition from a laminar type BL to a turbulent type BL. Our results further show that the relative slopes for scalar structure functions in the ESS scaling regime are the same as for their velocity counterparts, extending their previously established universality. The findings are confirmed by comparing to scalar structure functions in three-dimensional turbulent channel flow.

Taking the “Waste” Out of “Wastewater” for Human Water Security and Ecosystem Sustainability

Publisher: American Association for the Advancement of Science (AAAS)

Date: 10-08-2012

DOI: 10.1126/SCIENCE.1216852

Abstract: Humans create vast quantities of wastewater through inefficiencies and poor management of water systems. The wasting of water poses sustainability challenges, depletes energy reserves, and undermines human water security and ecosystem health. Here we review emerging approaches for reusing wastewater and minimizing its generation. These complementary options make the most of scarce freshwater resources, serve the varying water needs of both developed and developing countries, and confer a variety of environmental benefits. Their widespread adoption will require changing how freshwater is sourced, used, managed, and priced.

Hierarchical random additive process and logarithmic scaling of generalized high order, two-point correlations in turbulent boundary layer flow

Publisher: American Physical Society (APS)

Date: 13-06-2016

DOI: 10.1103/PHYSREVFLUIDS.1.024402

The Eddies and Scales of Wall Turbulence

Publisher: Cambridge University Press

Date: 06-12-2012

DOI: 10.1017/CBO9781139032810.006

Recovery of wall-shear stress to equilibrium flow conditions after a rough-to-smooth step change in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 10-06-2019

DOI: 10.1017/JFM.2019.351

Abstract: This paper examines the recovery of the wall-shear stress of a turbulent boundary layer that has undergone a sudden transition from a rough to a smooth surface. Early work of Antonia & Luxton ( J. Fluid Mech. , vol. 53, 1972, pp. 737–757) questioned the reliability of standard smooth-wall methods for measuring wall-shear stress in such conditions, and subsequent studies show significant disagreement depending on the approach used to determine the wall-shear stress downstream. Here we address this by utilising a collection of experimental databases at $Re_{\\unicode[STIX]{x1D70F}}\\approx 4100$ that have access to both ‘direct’ and ‘indirect’ measures of the wall-shear stress to understand the recovery to equilibrium conditions of the new surface. Our results reveal that the viscous region ( $z^{+}\\lesssim 4$ ) recovers almost immediately to an equilibrium state with the new wall conditions however, the buffer region and beyond takes several boundary layer thicknesses before recovering to equilibrium conditions, which is longer than previously thought. A unique direct numerical simulation database of a wall-bounded flow with a rough-to-smooth wall transition is employed to confirm these findings. In doing so, we present evidence that any estimate of the wall-shear stress from the mean velocity profile in the buffer region or further away from the wall tends to underestimate its magnitude in the near vicinity of the rough-to-smooth transition, and this is likely to be partly responsible for the large scatter of recovery lengths to equilibrium conditions reported in the literature. Our results also reveal that smaller energetic scales in the near-wall region recover to an equilibrium state associated with the new wall conditions within one boundary layer thickness downstream of the transition, while larger energetic scales exhibit an over-energised state for several boundary layer thicknesses downstream of the transition. Based on these observations, an alternative approach to estimating the wall-shear stress from the premultiplied energy spectrum is proposed.

On the streamwise evolution of turbulent boundary layers in arbitrary pressure gradients

Publisher: Cambridge University Press (CUP)

Date: 25-06-2002

DOI: 10.1017/S002211200200825X

Abstract: A new approach to the classic closure problem for turbulent boundary layers is presented. This involves, first, using the well-known mean-flow scaling laws such as the log law of the wall and the law of the wake of Coles (1956) together with the mean continuity and the mean momentum differential and integral equations. The important parameters governing the flow in the general non-equilibrium case are identified and are used for establishing a framework for closure. Initially closure is achieved here empirically and the potential for achieving closure in the future using the wall-wake attached eddy model of Perry & Marusic (1995) is outlined. Comparisons are made with experiments covering adverse-pressure-gradient flows in relaxing and developing states and flows approaching equilibrium sink flow. Mean velocity profiles, total shear stress and Reynolds stress profiles can be computed for different streamwise stations, given an initial upstream mean velocity profile and the streamwise variation of free-stream velocity. The attached eddy model of Perry & Marusic (1995) can then be utilized, with some refinement, to compute the remaining unknown quantities such as Reynolds normal stresses and associated spectra and cross-power spectra in the fully turbulent part of the flow.

An Extended View of the Inner-outer Interaction Model for Wall-bounded Turbulence Using Spectral Linear Stochastic Estimation

Publisher: Elsevier BV

Date: 2015

DOI: 10.1016/J.PROENG.2015.11.171

The WALLTURB Project

Publisher: Springer Netherlands

Date: 2011

DOI: 10.1007/978-90-481-9603-6_1

Friction factor decomposition for rough-wall flows: theoretical background and application to open-channel flows

Publisher: Cambridge University Press (CUP)

Date: 13-06-2019

DOI: 10.1017/JFM.2019.344

Abstract: A theoretically based relationship for the Darcy–Weisbach friction factor $f$ for rough-bed open-channel flows is derived and discussed. The derivation procedure is based on the double averaging (in time and space) of the Navier–Stokes equation followed by repeated integration across the flow. The obtained relationship explicitly shows that the friction factor can be split into at least five additive components, due to: (i) viscous stress (ii) turbulent stress (iii) dispersive stress (which in turn can be sub ided into two parts, due to bed roughness and secondary currents) (iv) flow unsteadiness and non-uniformity and (v) spatial heterogeneity of fluid stresses in a bed-parallel plane. These constitutive components account for the roughness geometry effect and highlight the significance of the turbulent and dispersive stresses in the near-bed region where their values are largest. To explore the potential of the proposed relationship, an extensive data set has been assembled by employing specially designed large-eddy simulations and laboratory experiments for a wide range of Reynolds numbers. Flows over self-affine rough boundaries, which are representative of natural and man-made surfaces, are considered. The data analysis focuses on the effects of roughness geometry (i.e. spectral slope in the bed elevation spectra), relative submergence of roughness elements and flow and roughness Reynolds numbers, all of which are found to be substantial. It is revealed that at sufficiently high Reynolds numbers the roughness-induced and secondary-currents-induced dispersive stresses may play significant roles in generating bed friction, complementing the dominant turbulent stress contribution.

Reynolds number effects on scale energy balance in wall turbulence

Publisher: AIP Publishing

Date: 2012

DOI: 10.1063/1.3673609

Abstract: The scale energy budget utilizes a modified version of the classical Kolmogorov equation of wall turbulence to develop an evolution equation for the second order structure function [R. J. Hill, “Exact second-order structure-function relationships,” J. Fluid Mech. 468, 317 (2002)]. This methodology allows for the simultaneous characterization of the energy cascade and spatial fluxes in turbulent shear flows across the entire physical domain as well as the range of scales. The present study utilizes this methodology to characterize the effects of Reynolds number on the balance of energy fluxes in turbulent channel flows. Direct numerical simulation data in the range Reτ = 300–934 are compared to previously published results at Reτ = 180 [N. Marati, C. M. Casciola, and R. Piva, “Energy cascade and spatial fluxes in wall turbulence,” J. Fluid Mech. 521, 191 (2004)]. The present results show no Reynolds number effects in the terms of the scale energy budget in either the viscous sublayer or buffer regions of the channel. In the logarithmic layer, the transfer of energy across scales clearly varies with Reynolds number, while the production of turbulent kinetic energy is not dependent on Reynolds number. An envelope of inverse energy cascade is quantified in the buffer region within which energy is transferred from small to larger scales. This envelope is observed in the range 6 & y+ & 37, where all scales except the smallest scales display characteristics of an inverse energy cascade. The cross-over scale lc+, which indicates the transition between production dominated and scale transfer dominated regimes, increases with Reynolds number, implying a larger range of transfer dominated scales, before the dominant mechanism switches to production. At higher Reynolds numbers, two distinct regimes of lc+ as a function of wall-normal location are observed, which was not captured at Reτ = 180. The variations of lc+ match the trends of the shear scale, which is a representation of the mean shear in the flow. Thus, this study demonstrates the utility and importance of the use of higher Reynolds number data in order to accurately characterize and understand the energy dynamics of various scales across the entire boundary layer.

Induced flow due to blowing and suction flow control: an analysis of transpiration

Publisher: Cambridge University Press (CUP)

Date: 25-11-2011

DOI: 10.1017/JFM.2011.441

Abstract: It has previously been demonstrated that the drag experienced by a Poiseuille flow in a channel can be reduced by subjecting the flow to a dynamic regime of blowing and suction at the walls of the channel (also known as ‘transpiration’). Furthermore, it has been found to be possible to induce a ‘bulk flow’, or steady motion through the channel, via transpiration alone. In this work, we derive explicit asymptotic expressions for the induced bulk flow via a perturbation analysis. From this we gain insight into the physical mechanisms at work within the flow. The boundary conditions used are of travelling sine waves at either wall, which may differ in litude and phase. Here it is demonstrated that the induced bulk flow results from the effect of convection. We find that the most effective arrangement for inducing a bulk flow is that in which the boundary conditions at either wall are equal in magnitude and opposite in sign. We also show that, for the bulk flow induced to be non-negligible, the wavelength of the boundary condition should be comparable to, or greater than, the height of the channel. Moreover, we derive the optimal frequency of oscillation, for maximising the induced bulk flow, under such boundary conditions. The asymptotic behaviour of the bulk flow is detailed within the conclusion. It is found, under certain caveats, that if the litude of the boundary condition is too great, the bulk flow induced will become dependent only upon the speed at which the boundary condition travels along the walls of the channel. We propose the conjecture that for all similar flows, if the magnitude of the transpiration is sufficiently great, the bulk flow will depend only upon the speed of the boundary condition.

Measuring physician practice, preparedness and preferences for genomic medicine: a national survey

Publisher: BMJ

Date: 07-2021

DOI: 10.1136/BMJOPEN-2020-044408

Abstract: Even as genomic medicine is implemented globally, there remains a lack of rigorous, national assessments of physicians’ current genomic practice and continuing genomics education needs. The aim of this study was to address this gap. A cross-sectional survey, informed by qualitative data and behaviour change theory, to assess the current landscape of Australian physicians’ genomic medicine practice, perceptions of proximity and in idual preparedness, and preferred models of practice and continuing education. The survey was advertised nationally through 10 medical colleges, 24 societies, 62 hospitals, social media, professional networks and snowballing. 409 medical specialists across Australia responded, representing 30 specialties (majority paediatricians, 20%), from mainly public hospitals (70%) in metropolitan areas (75%). Half (53%) had contacted their local genetics services and half (54%) had ordered or referred for a gene panel or exome/genome sequencing test in the last year. Two-thirds (67%) think genomics will soon impact their practice, with a significant preference for models that involved genetics services (p .0001). Currently, respondents mainly perform tasks associated with pretest family history taking and counselling, but more respondents expect to perform tasks at all stages of testing in the future, including tasks related to the test itself, and reporting results. While one-third (34%) recently completed education in genomics, only a quarter (25%) felt prepared to practise. Specialists would like (more) education, particularly on genomic technologies and clinical utility, and prefer this to be through varied educational strategies. This survey provides data from a breadth of physician specialties that can inform models of genetic service delivery and genomics education. The findings support education providers designing and delivering education that best meet learner needs to build a competent, genomic-literate workforce. Further analyses are underway to characterise early adopters of genomic medicine to inform strategies to increase engagement.

Assessment of dual plane PIV measurements in wall turbulence using DNS data

Publisher: Springer Science and Business Media LLC

Date: 27-06-2006

DOI: 10.1007/S00348-006-0168-Z

On the asymptotic similarity of the zero-pressure-gradient turbulent boundary layer

Publisher: Cambridge University Press (CUP)

Date: 10-12-2008

DOI: 10.1017/S0022112008004205

Abstract: We investigate similarity solutions for the outer part of a zero-pressure-gradient turbulent boundary layer in the limit of infinite Reynolds number. Previous work by George ( Phil. Trans. R. Soc . vol. 365, 2007 p. 789) has suggested that the only appropriate velocity scale for the outer region is U 1 , the free-stream velocity. This is based on the fact that scaling with U 1 leads to a mathematically valid similarity solution of the momentum equation for the outer region in the asymptotic limit of infinite Reynolds number. Here we show that the classical scaling using the friction velocity also leads to a valid similarity solution for the outer flow in this limit. Therefore on this basis it is not possible to dismiss the friction velocity as a possible scaling as has been suggested by George (2007) and others. We show that both the free-stream velocity and the friction velocity are potentially valid scalings according to this theoretical criterion.

Interfaces of uniform momentum zones in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 12-05-2017

DOI: 10.1017/JFM.2017.197

Abstract: In this paper we examine the characteristics of the interfaces that demarcate regions of relatively uniform streamwise momentum in turbulent boundary layers. The analysis utilises particle image velocimetry databases that span more than an order of magnitude of friction Reynolds number ( $Re_{\\unicode[STIX]{x1D70F}}=10^{3}$ – $10^{4}$ ), enabling us to provide a detailed description of the interfacial layers as a function of Reynolds number. As reported by Adrian et al. ( J. Fluid Mech. , vol. 422, 2000, pp. 1–54), these interfaces appear as persistent regions of strong shear with distinct patches of vorticity consistent with a packet-like structure. Here, however, we treat these interfaces as continuous lines, thus averaging the properties of the vortical patches, and find that their geometry is highly contorted and exhibits self-similarity across a wide range of scales. Specifically, the lengths of the edges of uniform momentum zones exhibit a power-law behaviour with a fractal scaling that has a constant exponent across the boundary layer, while the topmost edge or the turbulent/non-turbulent interface shows a sudden increase in the exponent. The accompanying sharp changes in velocity that occur at these edges are found to change in magnitude as a function of wall-normal height, being larger closer to the wall. Further, a Reynolds number invariance is exhibited when the magnitude of the step-like changes in velocity is scaled by the skin-friction velocity, meanwhile, the width across which it occurs is shown to be of the order of the Taylor microscale. Based on these quantitative measures, the Reynolds number scaling observed and the persistent presence of sharp changes in momentum in turbulent boundary layers, a simple model is used to reconstruct the mean velocity profile. Insight gained from the model enhances our understanding of how instantaneous phenomena (such as a zonal-like structural arrangement) manifests in the averaged flow statistics and confirms that the instantaneous momentum in a turbulent boundary layer appears to mainly consist of a step-like profile as a function of wall-normal distance.

Effectively visualizing multi-valued flow data using color and texture

Publisher: IEEE

Date: 2003

DOI: 10.1109/VISUAL.2003.1250362

High-fidelity computational study of roughness effects on high pressure turbine performance and heat transfer

Publisher: Elsevier BV

Date: 06-2023

DOI: 10.1016/J.IJHEATFLUIDFLOW.2023.109134

Climate change and its implications for Australia's freshwater fish

Publisher: CSIRO Publishing

Date: 2011

DOI: 10.1071/MF10308

Abstract: Freshwater environments and their fishes are particularly vulnerable to climate change because the persistence and quality of aquatic habitat depend heavily on climatic and hydrologic regimes. In Australia, projections indicate that the rate and magnitude of climate change will vary across the continent. We review the likely effects of these changes on Australian freshwater fishes across geographic regions encompassing a ersity of habitats and climatic variability. Commonalities in the predicted implications of climate change on fish included habitat loss and fragmentation, surpassing of physiological tolerances and spread of alien species. Existing anthropogenic stressors in more developed regions are likely to compound these impacts because of the already reduced resilience of fish assemblages. Many Australian freshwater fish species are adapted to variable or unpredictable flow conditions and, in some cases, this evolutionary history may confer resistance or resilience to the impacts of climate change. However, the rate and magnitude of projected change will outpace the adaptive capacities of many species. Climate change therefore seriously threatens the persistence of many of Australia’s freshwater fish species, especially of those with limited ranges or specific habitat requirements, or of those that are already occurring close to physiological tolerance limits. Human responses to climate change should be proactive and focus on maintaining population resilience through the protection of habitat, mitigation of current anthropogenic stressors, adequate planning and provisioning of environmental flows and the consideration of more interventionist options such as managed translocations.

Turbulence wall-shear stress sensor for the atmospheric surface layer

Publisher: IOP Publishing

Date: 11-07-2005

DOI: 10.1088/0957-0233/16/8/015

Strategies for the visualization of multiple 2D vector fields

Publisher: Institute of Electrical and Electronics Engineers (IEEE)

Date: 07-2006

DOI: 10.1109/MCG.2006.88

Multiscale Geometry and Scaling of the Turbulent-Nonturbulent Interface in High Reynolds Number Boundary Layers

Publisher: American Physical Society (APS)

Date: 24-07-2013

DOI: 10.1103/PHYSREVLETT.111.044501

Anthony Edward Perry 1937 - 2001

Publisher: CSIRO Publishing

Date: 2010

DOI: 10.1071/HR09022

Abstract: Tony Perry was one of Australia's most outstanding researchers in fluid mechanics, particularly in the study of turbulent fluid motion. He was a gifted experimentalist who advanced the techniques of hot-wire anemometry and quantitative flow visualization to make measurements of unparalleled accuracy to answer fundamental scaling questions. He also made seminal theoretical contributions to the physical modelling of wall-bounded turbulence, and pioneered flow topology approaches for the classification and description of fluid motions. He was a gifted lecturer, devoted supervisor to twenty PhD students, and a passionate and enthusiastic influence on numerous colleagues around the world.

Are surgical masks manufactured from sterilisation wrap safe?

Publisher: Elsevier BV

Date: 05-2021

DOI: 10.1016/J.IDH.2020.11.001

Laminar boundary layer on an impulsively started rotating sphere

Publisher: AIP Publishing

Date: 1979

DOI: 10.1063/1.862466

Abstract: The problem of determining the development with time of the flow of a viscous incompressible fluid outside a rotating sphere is considered. The sphere is started impulsively from rest to rotate with constant angular velocity about a diameter. The motion is governed by a coupled set of three nonlinear time-dependent partial differential equations which are solved by first employing the semi-analytical method of series truncation to reduce the number of independent variables by one and then solving numerically a finite set of partial differential equations in one space variable and the time. The calculations have been carried out on the assumption that the Reynolds number is very large. The physical properties of the flow are calculated as functions of the time and compared with existing solutions for large and small times. A radial jet is found to develop with time near the equator of the sphere as a consequence of the collision of the boundary layers.

Study of the Streamwise Evolution of Turbulent Boundary Layers to High Reynolds Numbers

Publisher: Springer International Publishing

Date: 31-08-2016

DOI: 10.1007/978-3-319-41217-7_3

Reynolds number trend of hierarchies and scale interactions in turbulent boundary layers

Publisher: The Royal Society

Date: 13-03-2017

DOI: 10.1098/RSTA.2016.0077

Abstract: Small-scale velocity fluctuations in turbulent boundary layers are often coupled with the larger-scale motions. Studying the nature and extent of this scale interaction allows for a statistically representative description of the small scales over a time scale of the larger, coherent scales. In this study, we consider temporal data from hot-wire anemometry at Reynolds numbers ranging from Re τ ≈2800 to 22 800, in order to reveal how the scale interaction varies with Reynolds number. Large-scale conditional views of the representative litude and frequency of the small-scale turbulence, relative to the large-scale features, complement the existing consensus on large-scale modulation of the small-scale dynamics in the near-wall region. Modulation is a type of scale interaction, where the litude of the small-scale fluctuations is continuously proportional to the near-wall footprint of the large-scale velocity fluctuations. Aside from this litude modulation phenomenon, we reveal the influence of the large-scale motions on the characteristic frequency of the small scales, known as frequency modulation. From the wall-normal trends in the conditional averages of the small-scale properties, it is revealed how the near-wall modulation transitions to an intermittent-type scale arrangement in the log-region. On average, the litude of the small-scale velocity fluctuations only deviates from its mean value in a confined temporal domain, the duration of which is fixed in terms of the local Taylor time scale. These concentrated temporal regions are centred on the internal shear layers of the large-scale uniform momentum zones, which exhibit regions of positive and negative streamwise velocity fluctuations. With an increasing scale separation at high Reynolds numbers, this interaction pattern encompasses the features found in studies on internal shear layers and concentrated vorticity fluctuations in high-Reynolds-number wall turbulence. This article is part of the themed issue ‘Toward the development of high-fidelity models of wall turbulence at large Reynolds number’.

A predictive inner–outer model for streamwise turbulence statistics in wall-bounded flows

Publisher: Cambridge University Press (CUP)

Date: 05-07-2011

DOI: 10.1017/JFM.2011.216

Abstract: A model is proposed with which the statistics of the fluctuating streamwise velocity in the inner region of wall-bounded turbulent flows are predicted from a measured large-scale velocity signature from an outer position in the logarithmic region of the flow. Results, including spectra and all moments up to sixth order, are shown and compared to experimental data for zero-pressure-gradient flows over a large range of Reynolds numbers. The model uses universal time-series and constants that were empirically determined from zero-pressure-gradient boundary layer data. In order to test the applicability of these for other flows, the model is also applied to channel, pipe and adverse-pressure-gradient flows. The results support the concept of a universal inner region that is modified through a modulation and superposition of the large-scale outer motions, which are specific to the geometry or imposed streamwise pressure gradient acting on the flow.

Wall-bounded turbulence

Publisher: AIP Publishing

Date: 09-2013

DOI: 10.1063/PT.3.2114

Abstract: New experimental insights could pave the way for leaner, faster simulations of turbulent fluid flow.

The topology of skin friction and surface vorticity fields in wall-bounded flows

Publisher: Informa UK Limited

Date: 2012

DOI: 10.1080/14685248.2012.663093

Statistics of turbulence in the energy-containing range of Taylor–Couette compared to canonical wall-bounded flows

Publisher: Cambridge University Press (CUP)

Date: 06-10-2017

DOI: 10.1017/JFM.2017.625

Abstract: Considering structure functions of the streamwise velocity component in a framework akin to the extended self-similarity hypothesis (ESS), de Silva et al. ( J. Fluid Mech. , vol. 823, 2017, pp. 498–510) observed that remarkably the large-scale (energy-containing range) statistics in canonical wall-bounded flows exhibit universal behaviour. In the present study, we extend this universality, which was seen to encompass also flows at moderate Reynolds number, to Taylor–Couette flow. In doing so, we find that also the transversal structure function of the spanwise velocity component exhibits the same universal behaviour across all flow types considered. We further demonstrate that these observations are consistent with predictions developed based on an attached-eddy hypothesis. These considerations also yield a possible explanation for the efficacy of the ESS framework by showing that it relaxes the self-similarity assumption for the attached-eddy contributions. By taking the effect of streamwise alignment into account, the attached-eddy model predicts different behaviour for structure functions in the streamwise and in the spanwise directions and that this effect cancels in the ESS framework – both consistent with the data. Moreover, it is demonstrated here that also the additive constants, which were previously believed to be flow dependent, are indeed universal at least in turbulent boundary layers and pipe flow where high Reynolds number data are currently available.

Evolution of zero-pressure-gradient boundary layers from different tripping conditions

Publisher: Cambridge University Press (CUP)

Date: 22-10-2015

DOI: 10.1017/JFM.2015.556

Abstract: In this paper we study the spatial evolution of zero-pressure-gradient (ZPG) turbulent boundary layers from their origin to a canonical high-Reynolds-number state. A prime motivation is to better understand under what conditions reliable scaling behaviour comparisons can be made between different experimental studies at matched local Reynolds numbers. This is achieved here through detailed streamwise velocity measurements using hot wires in the large University of Melbourne wind tunnel. By keeping the unit Reynolds number constant, the flow conditioning, contraction and trip can be considered unaltered for a given boundary layer’s development and hence its evolution can be studied in isolation from the influence of inflow conditions by moving to different streamwise locations. Careful attention was given to the experimental design in order to make comparisons between flows with three different trips while keeping all other parameters nominally constant, including keeping the measurement sensor size nominally fixed in viscous wall units. The three trips consist of a standard trip and two deliberately ‘over-tripped’ cases, where the initial boundary layers are over-stimulated with additional large-scale energy. Comparisons of the mean flow, normal Reynolds stress, spectra and higher-order turbulence statistics reveal that the effects of the trip are seen to be significant, with the remnants of the ‘over-tripped’ conditions persisting at least until streamwise stations corresponding to $Re_{x}=1.7\\times 10^{7}$ and $x=O(2000)$ trip heights are reached (which is specific to the trips used here), at which position the non-canonical boundary layers exhibit a weak memory of their initial conditions at the largest scales $O(10{\\it\\delta})$ , where ${\\it\\delta}$ is the boundary layer thickness. At closer streamwise stations, no one-to-one correspondence is observed between the local Reynolds numbers ( $Re_{{\\it\\tau}}$ , $Re_{{\\it\\theta}}$ or $Re_{x}$ etc.), and these differences are likely to be the cause of disparities between previous studies where a given Reynolds number is matched but without account of the trip conditions and the actual evolution of the boundary layer. In previous literature such variations have commonly been referred to as low-Reynolds-number effects, while here we show that it is more likely that these differences are due to an evolution effect resulting from the initial conditions set up by the trip and/or the initial inflow conditions. Generally, the mean velocity profiles were found to approach a constant wake parameter ${\\it\\Pi}$ as the three boundary layers developed along the test section, and agreement of the mean flow parameters was found to coincide with the location where other statistics also converged, including higher-order moments up to tenth order. This result therefore implies that it may be sufficient to document the mean flow parameters alone in order to ascertain whether the ZPG flow, as described by the streamwise velocity statistics, has reached a canonical state, and a computational approach is outlined to do this. The computational scheme is shown to agree well with available experimental data.

Temporally optimized spanwise vorticity sensor measurements in turbulent boundary layers

Publisher: Springer Science and Business Media LLC

Date: 28-11-2015

DOI: 10.1007/S00348-015-2084-6

On the role of large-scale structures in wall turbulence

Publisher: AIP Publishing

Date: 03-2001

DOI: 10.1063/1.1343480

Abstract: Recent experimental and computational studies by Adrian and co-workers, such as Adrian et al. [J. Fluid Mech. 422, 1 (2000)] and Zhou et al. [J. Fluid Mech. 387, 353 (1999)], have proposed that a dominant structure in wall turbulence is the organization of hairpin vortices in spatially correlated packets or trains of vortices. In this study this scenario is investigated using the attached eddy model of Perry and Marusic [J. Fluid Mech. 298, 361 (1995)] by calculating structure angles, two-point velocity correlations and autocorrelations and comparing them to experimental measurements across a zero-pressure-gradient turbulent boundary layer. The results support the conclusion that spatially coherent packets are a statistically significant structure for Reynolds stresses and transport processes in the logarithmic region of the flow.

Moment generating functions and scaling laws in the inertial layer of turbulent wall-bounded flows

Publisher: Cambridge University Press (CUP)

Date: 16-02-2016

DOI: 10.1017/JFM.2016.82

Abstract: Properties of single- and two-point moment generating functions (MGFs) are examined in the inertial region of wall-bounded flows. Empirical evidence for power-law scaling of the single-point MGF $\\langle \\text{exp}(qu^{+})\\rangle$ (where $u^{+}$ is the normalized streamwise velocity fluctuation and $q$ a real parameter) with respect to the wall-normal distance is presented, based on hot-wire data from a $Re_{{\\it\\tau}}=13\\,000$ boundary-layer experiment. The parameter $q$ serves as a ‘dial’ to emphasize different parts of the signal such as high- and low-speed regions, for positive and negative values of $q$ , respectively. Power-law scaling $\\langle \\text{exp}(qu^{+})\\rangle \\sim (z/{\\it\\delta})^{-{\\it\\tau}(q)}$ can be related to the generalized logarithmic laws previously observed in higher-order moments, such as in $\\langle u^{+2p}\\rangle ^{1 }$ , but provide additional information not available through traditional moments if considering $q$ values away from the origin. For two-point MGFs, the scalings in $\\langle \\text{exp}[qu^{+}(x)+q^{\\prime }u^{+}(x+r)]\\rangle$ with respect to $z$ and streamwise displacement $r$ in the logarithmic region are investigated. The special case $q^{\\prime }=-q$ is of particular interest, since this choice emphasizes rare events with high and low speeds at a distance $r$ . Applying simple scaling arguments motivated by the attached eddy model, a ‘scaling transition’ is predicted to occur for $q=q_{cr}$ such that ${\\it\\tau}(q_{cr})+{\\it\\tau}(-q_{cr})=1$ , where ${\\it\\tau}(q)$ is the set of scaling exponents for single-point MGFs. This scaling transition is not visible to traditional central moments, but is indeed observed based on the experimental data, illustrating the capabilities of MGFs to provide new and statistically robust insights into turbulence structure and confirming essential ingredients of the attached eddy model.

On the universality of inertial energy in the log layer of turbulent boundary layer and pipe flows

Publisher: Springer Science and Business Media LLC

Date: 25-06-2015

DOI: 10.1007/S00348-015-1994-7

Structure function tensor scaling in the logarithmic region derived from the attached eddy model of wall-bounded turbulent flows

Publisher: American Physical Society (APS)

Date: 05-06-2017

DOI: 10.1103/PHYSREVFLUIDS.2.064602

Forcing frequency effects on turbulence dynamics in pulsatile pipe flow

Publisher: Elsevier BV

Date: 04-2020

DOI: 10.1016/J.IJHEATFLUIDFLOW.2020.108538

Characterising Momentum Flux Events in High Reynolds Number Turbulent Boundary Layers

Publisher: MDPI AG

Date: 20-04-2021

DOI: 10.3390/FLUIDS6040168

Abstract: The momentum flux in a canonical turbulent boundary layer is known to have a time-series signature that is characterised by a highly intermittent variation, which includes very short periods of intense flux activity. Here, we study the variation in these flux signal characteristics across almost a decade of flow Reynolds number (Reτ) by analysing datasets acquired using miniature cross-wire probes with matched spatial resolution. The analysis is facilitated by conditionally s ling the signal based on the quadrant (Qi i = 1–4) and magnitude of the flux, revealing fractional cumulative contribution from Q4 to increase at a much faster rate than from Q2 with Reτ. An episodic description of the flux signal is subsequently undertaken, which associates this rapid increase in Q4 contributions with the emergence of extreme and rare flux events with Reτ. The same dataset is also used to test Townsend’s hypothesis on the active and inactive components of the momentum flux, which are obtained for the first time by implementing a spectral linear stochastic estimation-based decomposition methodology. While the active component is found to be the dominant contributor to the mean momentum flux consistent with Townsend’s hypothesis, the inactive component is found to be small but non-zero, owing to the non-linear interactions associated with the modulation phenomenon. Finally, an episodic description of the active and inactive momentum flux signal is undertaken to highlight the starkly different time series characteristics of the two flux components. The inactive flux signal is found to comprise in idual statistically significant events associated with all four quadrants, leading to a small net contribution to the total flux.

Minimization of divergence error in volumetric velocity measurements and implications for turbulence statistics

Publisher: Springer Science and Business Media LLC

Date: 22-06-2013

DOI: 10.1007/S00348-013-1557-8

Response to “Letter to the Editor Regarding ‘Crossing Turbulent Boundaries: Interfacial Flux in Environmental Flows’”

Publisher: American Chemical Society (ACS)

Date: 24-04-2012

DOI: 10.1021/ES301452K

Hot-wire spatial resolution issues in wall-bounded turbulence

Publisher: Cambridge University Press (CUP)

Date: 10-09-2009

DOI: 10.1017/S0022112009007721

Abstract: Careful reassessment of new and pre-existing data shows that recorded scatter in the hot-wire-measured near-wall peak in viscous-scaled streamwise turbulence intensity is due in large part to the simultaneous competing effects of the Reynolds number and viscous-scaled wire length l + . An empirical expression is given to account for these effects. These competing factors can explain much of the disparity in existing literature, in particular explaining how previous studies have incorrectly concluded that the inner-scaled near-wall peak is independent of the Reynolds number. We also investigate the appearance of the so-called outer peak in the broadband streamwise intensity, found by some researchers to occur within the log region of high-Reynolds-number boundary layers. We show that the ‘outer peak’ is consistent with the attenuation of small scales due to large l + . For turbulent boundary layers, in the absence of spatial resolution problems, there is no outer peak up to the Reynolds numbers investigated here ( Re τ = 18830). Beyond these Reynolds numbers – and for internal geometries – the existence of such peaks remains open to debate. Fully mapped energy spectra, obtained with a range of l + , are used to demonstrate this phenomenon. We also establish the basis for a ‘maximum flow frequency’, a minimum time scale that the full experimental system must be capable of resolving, in order to ensure that the energetic scales are not attenuated. It is shown that where this criterion is not met (in this instance due to insufficient anemometer robe response), an outer peak can be reproduced in the streamwise intensity even in the absence of spatial resolution problems. It is also shown that attenuation due to wire length can erode the region of the streamwise energy spectra in which we would normally expect to see k x −1 scaling. In doing so, we are able to rationalize much of the disparity in pre-existing literature over the k x −1 region of self-similarity. Not surprisingly, the attenuated spectra also indicate that Kolmogorov-scaled spectra are subject to substantial errors due to wire spatial resolution issues. These errors persist to wavelengths far beyond those which we might otherwise assume from simple isotropic assumptions of small-scale motions. The effects of hot-wire length-to-diameter ratio ( l / d ) are also briefly investigated. For the moderate wire Reynolds numbers investigated here, reducing l / d from 200 to 100 has a detrimental effect on measured turbulent fluctuations at a wide range of energetic scales, affecting both the broadband intensity and the energy spectra.

Dazzled by shine: gloss as an antipredator strategy in fast moving prey

Publisher: Oxford University Press (OUP)

Date: 08-06-2023

DOI: 10.1093/BEHECO/ARAD046

Abstract: Previous studies on stationary prey have found mixed results for the role of a glossy appearance in predator avoidance—some have found that glossiness can act as warning coloration or improve camouflage, whereas others detected no survival benefit. An alternative untested hypothesis is that glossiness could provide protection in the form of dynamic dazzle. Fast moving animals that are glossy produce flashes of light that increase in frequency at higher speeds, which could make it harder for predators to track and accurately locate prey. We tested this hypothesis by presenting praying mantids with glossy or matte targets moving at slow and fast speed. Mantids were less likely to strike glossy targets, independently of speed. Additionally, mantids were less likely to track glossy targets and more likely to hit the target with one out of the two legs that struck rather than both raptorial legs, but only when targets were moving fast. These results support the hypothesis that a glossy appearance may have a function as an antipredator strategy by reducing the ability of predators to track and accurately target fast moving prey.

Smooth- and rough-wall boundary layer structure from high spatial range particle image velocimetry

Publisher: American Physical Society (APS)

Date: 07-10-2016

DOI: 10.1103/PHYSREVFLUIDS.1.064402

The effect of spanwise wavelength of surface heterogeneity on turbulent secondary flows

Publisher: Cambridge University Press (CUP)

Date: 29-04-2020

DOI: 10.1017/JFM.2020.262

Vertical Coherence of Turbulence in the Atmospheric Surface Layer: Connecting the Hypotheses of Townsend and Davenport

Publisher: Springer Science and Business Media LLC

Date: 05-04-2019

DOI: 10.1007/S10546-019-00445-4

Some predictions of the attached eddy model for a high Reynolds number boundary layer

Publisher: The Royal Society

Date: 16-01-2007

DOI: 10.1098/RSTA.2006.1950

Abstract: Many flows of practical interest occur at high Reynolds number, at which the flow in most of the boundary layer is turbulent, showing apparently random fluctuations in velocity across a wide range of scales. The range of scales over which these fluctuations occur increases with the Reynolds number and hence high Reynolds number flows are difficult to compute or predict. In this paper, we discuss the structure of these flows and describe a physical model, based on the attached eddy hypothesis, which makes predictions for the statistical properties of these flows and their variation with Reynolds number. The predictions are shown to compare well with the results from recent experiments in a new purpose-built high Reynolds number facility. The model is also shown to provide a clear physical explanation for the trends in the data. The limits of applicability of the model are also discussed.

Unravelling turbulence near walls

Publisher: Cambridge University Press (CUP)

Date: 10-07-2009

DOI: 10.1017/S0022112009007708

Abstract: Turbulent flows near walls have been the focus of intense study since their first description by Ludwig Prandtl over 100 years ago. They are critical in determining the drag and lift of an aircraft wing for ex le. Key challenges are to understand the physical mechanisms causing the transition from smooth, laminar flow to turbulent flow and how the turbulence is then maintained. Recent direct numerical simulations have contributed significantly towards this understanding.

On the different contributions of coherent structures to the spectra of a turbulent round jet and a turbulent boundary layer

Publisher: Cambridge University Press (CUP)

Date: 26-11-2001

DOI: 10.1017/S002211200100619X

Abstract: This paper examines and compares spectral measurements from a turbulent round jet and a turbulent boundary layer. The conjecture that is examined is that both flows consist of coherent structures immersed in a background of isotropic turbulence. In the case of the jet, a single size of coherent structure is considered, whereas in the boundary layer there are a range of sizes of geometrically similar structures. The conjecture is examined by comparing experimental measurements of spectra for the two flows with the spectra calculated using models based on simple vortex structures. The universality of the small scales is considered by comparing high-wavenumber experimental spectra. It is shown that these simple structural models give a good account of the turbulent flows.

Amplitude and frequency modulation in wall turbulence

Publisher: Cambridge University Press (CUP)

Date: 27-09-2012

DOI: 10.1017/JFM.2012.398

Abstract: In this study we examine the impact of the strength of the large-scale motions on the litude and frequency of the small scales in high-Reynolds-number turbulent boundary layers. Time series of hot-wire data are decomposed into large- and small-scale components, and the impact of the large scale on the litude and frequency of the small scales is considered. The litude modulation effect is examined by conditionally averaging the small-scale intensity ( ${ u}_{S}^{2} $ ) for various values of the large-scale fluctuation ( ${u}_{L} $ ). It is shown that ${ u}_{S}^{2} $ increases with increasing value of ${u}_{L} $ in the near-wall region, whereas, farther away from the wall, ${ u}_{S}^{2} $ decreases with increasing ${u}_{L} $ . The rate of increase in small-scale intensity with the strength of the large-scale signal is neither symmetric (about ${u}_{L} = 0$ ) nor linear. The extent of the frequency modulation is examined by counting the number of occurrences of local maxima or minima in the small-scale signal. It is shown that the frequency modulation effect is confined to the near-wall region and its extent diminishes rapidly beyond ${y}^{+ } = 100$ . A phase lag between the large- and small-scale fluctuations, in terms of litude modulation, has also been identified, which is in agreement with previous studies. The phase lag between large- and small-scale fluctuations for frequency modulation is comparable to that of litude modulation in the near-wall region. The combined effect of both litude and frequency modulation is also examined by computing conditional spectra of the small-scale signal conditioned on the large scales. In the near-wall region, the results indicate that the peak value of pre-multiplied spectra increases with increasing value of ${u}_{L} $ , indicating litude modulation, while the frequency at which this peak occurs also increases with increasing value of ${u}_{L} $ , revealing frequency modulation. The overall trends observed from the conditional spectra are consistent with the results obtained through statistical analyses. Finally, a physical mechanism that can capture most of the above observations is also presented.

Evidence that superstructures comprise self-similar coherent motions in high Reynolds number boundary layers

Publisher: Cambridge University Press (CUP)

Date: 11-08-2023

DOI: 10.1017/JFM.2023.566

Abstract: We present experimental evidence that the superstructures in turbulent boundary layers comprise smaller, geometrically self-similar coherent motions. The evidence comes from identifying and analysing instantaneous superstructures from large-scale particle image velocimetry datasets acquired at high Reynolds numbers, capable of capturing streamwise elongated motions extending up to 12 times the boundary layer thickness. Given the challenge in identifying the constituent motions of the superstructures based on streamwise velocity signatures, a new approach is adopted that analyses the wall-normal velocity fluctuations within these very long motions, which reveals the constituent motions unambiguously. The conditional streamwise energy spectra of the Reynolds shear stress and the wall-normal fluctuations, corresponding exclusively to the superstructure region, are found to exhibit the well-known distance-from-the-wall scaling in the intermediate-scale range. It suggests that geometrically self-similar motions are the constituent motions of these very-large-scale structures. Investigation of the spatial organization of the wall-normal momentum-carrying eddies, within the superstructures, also lends empirical support to the concatenation hypothesis for the formation of these structures. The association between the superstructures and self-similar motions is reaffirmed on comparing the vertical coherence of the Reynolds-shear-stress-carrying motions, by computing conditionally averaged two-point correlations, which are found to match with the mean correlations. The mean vertical coherence of these motions, investigated for the log region across three decades of Reynolds numbers, exhibits a unique distance-from-the-wall scaling invariant with Reynolds number. The findings support modelling of these dynamically significant motions via data-driven coherent structure-based models.

Energy transfer in turbulent channel flows and implications for resolvent modelling

Publisher: Cambridge University Press (CUP)

Date: 25-01-2021

DOI: 10.1017/JFM.2020.929

Spanwise velocity statistics in high-Reynolds-number turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 02-03-2021

DOI: 10.1017/JFM.2020.1129

Wavelet analysis of wall turbulence to study large-scale modulation of small scales

Publisher: Springer Science and Business Media LLC

Date: 23-09-2015

DOI: 10.1007/S00348-015-2058-8

An upstream migration fought with danger

Publisher: Wiley

Date: 10-04-2017

DOI: 10.1002/ECY.1737

Evidence of very long meandering features in the logarithmic region of turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 02-05-2007

DOI: 10.1017/S0022112006003946

Abstract: A regime of very long meandering positive and negative streamwise velocity fluctuations, that we term ‘superstructures’, are found to exist in the log and lower wake regions of turbulent boundary layers. Measurements are made with a spanwise rake of 10 hot-wires in two separate facilities (spanning more than a decade of Re τ ) and are compared with existing PIV and DNS results. In all cases, we note evidence of a large-scale stripiness in the streamwise velocity fluctuations. The length of these regions can commonly exceed 20δ. Similar length scales have been previously reported for pipes and DNS channel flows. It is suggested that the true length of these features is masked from single-point statistics (such as autocorrelations and spectra) by a spanwise meandering tendency. Support for this conjecture is offered through the study of a synthetic flow composed only of sinusoidally meandering elongated low- and high-speed regions. From detailed maps of one-dimensional spectra, it is found that the contribution to the streamwise turbulence intensities associated with the superstructures appears to be increasingly significant with Reynolds number, and scales with outer length variables (δ). Importantly, the superstructure maintains a presence or footprint in the near-wall region, seeming to modulate or influence the near-wall cycle. This input of low-wavenumber outer-scaled energy into the near-wall region is consistent with the rise in near-wall streamwise intensities, when scaled with inner variables, that has been noted to occur with increasing Reynolds number. In an attempt to investigate these structures at very high Reynolds numbers, we also report on recent large-scale sonic anemometer rake measurements, made in the neutrally stable atmospheric surface layer. Preliminary results indicate that the superstructure is present in the log region of this atmospheric flow at Re τ = 6.6×10 5 , and has a size consistent with outer scaling.

Two-dimensional cross-spectrum of the streamwise velocity in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 02-03-2020

DOI: 10.1017/JFM.2020.139

Scale-dependent inclination angle of turbulent structures in stratified atmospheric surface layers

Publisher: Cambridge University Press (CUP)

Date: 23-05-2014

DOI: 10.1017/JFM.2022.403

Abstract: A large-scale spanwise and wall-normal array of sonic anemometers in the atmospheric surface layer is used to acquire all three components of instantaneous fluctuating velocity as well as temperature in a range of stability conditions. These data permit investigation of the three-dimensional statistical structure of turbulence structures. Based on a similar dataset, Krug et al. ( Boundary-Layer Meteorol. , vol. 172, 2019, pp. 199–214) reported a self-similar range of wall-attached turbulence structures under both unstable and near-neutral stability conditions. They considered only a wall-normal array and thus assessed statistical structure in the wall-normal direction, in relation to the streamwise wavelength. The present work extends the view of a self-similar range of turbulence structures, by including the statistical structure in the spanwise direction. Moreover, by analysing the phase shift between synchronized measurements in the spectral domain, it is inferred how a scale-dependent inclination angle in the streamwise/wall-normal plane varies with stability. Results suggest that the self-similar wall-attached structures have similar aspect ratios between streamwise/wall-normal scales and streamwise/spanwise scales such that $\\lambda _x/\\Delta z : \\lambda _x/\\Delta y \\approx 1$ for both near-neutral and unstable conditions. Under the most unstable conditions, coherent structures with $\\lambda _x/\\delta = 1$ are inclined at angles as high as $65^{\\circ }$ relative to the solid boundary, while larger scales $\\lambda _x/\\delta = 6$ exhibit inclination angles of approximately $35^{\\circ }$ . For near-neutral stability conditions, the angle tends towards $12^{\\circ }$ for all scales. It is noted that in the near-neutral condition, the structure inclination angle and the aspect ratio – and thus the statistical modelling of coherent structures in the atmospheric surface layer – are highly sensitive to the value of the stability parameter.

Hierarchical random additive model for the spanwise and wall-normal velocities in wall-bounded flows at high Reynolds numbers

Publisher: American Physical Society (APS)

Date: 17-12-2018

DOI: 10.1103/PHYSREVFLUIDS.3.124606

Self-similarity in the inertial region of wall turbulence

Publisher: American Physical Society (APS)

Date: 24-12-2014

DOI: 10.1103/PHYSREVE.90.063015

The statistical behaviour of attached eddies

Publisher: AIP Publishing

Date: 2015

DOI: 10.1063/1.4905301

Abstract: Townsend’s attached eddy hypothesis forms the basis of an established model of the logarithmic layer in wall-bounded turbulent flows in which this inertially dominated region is characterised by a hierarchy of geometrically self-similar eddying motions that scale with their distance to the wall. The hypothesis has gained considerable support from high Reynolds number measurements of the second-order moments of the fluctuating velocities. Recently, Meneveau and Marusic [“Generalized logarithmic law for high-order moments in turbulent boundary layers,” J. Fluid Mech. 719, R1 (2013)] presented experimental evidence that all even-ordered moments of the streamwise velocity will exhibit a logarithmic dependence on the distance from the wall. They demonstrated that this was consistent with the attached eddy hypothesis, so long as the velocity distribution is assumed to be Gaussian (which allows the use of the central limit theorem). In this paper, we derive this result from the attached eddy model without assuming a Gaussian velocity distribution, and find that such logarithmic behaviours are valid in the large Reynolds number limit. We also revisit the physical and mathematical basis of the attached eddy hypothesis, in order to increase rigour and minimise the assumptions required to apply the hypothesis. To this end, we have extended the proof of C bell’s theorem to apply to the velocity field corresponding to a forest of variously sized eddies that are randomly placed on the wall. This enables us to derive all moments of the velocity in the logarithmic region, including cross-correlations between different components of the velocity. By contrast, previous studies of the attached eddy hypothesis have considered only the mean velocity and its second order moments. From this, we obtain qualitatively correct skewnesses and flatnesses for the spanwise and wall-normal fluctuations. The issue of the Reynolds number dependence of von Kármán’s constant is also addressed.

Urban transformations: booms, busts and other catastrophes: 11th Australasian Urban History/Planning History Conference, Perth, 2012

Publisher: Informa UK Limited

Date: 10-2012

DOI: 10.1080/02665433.2012.709697

Progress in Wall Turbulence 2

Publisher: Springer International Publishing

Date: 2016

DOI: 10.1007/978-3-319-20388-1

Coriolis effect on centrifugal buoyancy-driven convection in a thin cylindrical shell

Publisher: Cambridge University Press (CUP)

Date: 15-01-2021

DOI: 10.1017/JFM.2020.959

Turbulent drag reduction by spanwise wall forcing.

Publisher: Cambridge University Press (CUP)

Date: 28-07-2023

DOI: 10.1017/JFM.2023.498

Abstract: We present measurements of turbulent drag reduction (DR) in boundary layers at high friction Reynolds numbers in the range of $4500 \\le Re_\\tau \\le 15\\ 000$ . The efficacy of the approach, using streamwise travelling waves of spanwise wall oscillations, is studied for two actuation regimes: (i) inner-scaled actuation (ISA), as investigated in Part 1 of this study, which targets the relatively high-frequency structures of the near-wall cycle, and (ii) outer-scaled actuation (OSA), which was recently presented by Marusic et al. ( Nat. Commun. , vol. 12, 2021) for high- $Re_\\tau$ flows, targeting the lower-frequency, outer-scale motions. Multiple experimental techniques were used, including a floating-element balance to directly measure the skin-friction drag force, hot-wire anemometry to acquire long-time fluctuating velocity and wall-shear stress, and stereoscopic particle image velocimetry to measure the turbulence statistics of all three velocity components across the boundary layer. Under the ISA pathway, DR of up to 25 % was achieved, but mostly with net power saving (NPS) losses due to the high-input power cost associated with the high-frequency actuation. The low-frequency OSA pathway, however, with its lower input power requirements, was found to consistently result in positive NPS of 5–10 % for moderate DRs of 5–15 %. The results suggest that OSA is an attractive pathway for energy-efficient DR in high-Reynolds-number applications.

Fully resolved measurements of turbulent boundary layer flows up to

Publisher: Cambridge University Press (CUP)

Date: 20-07-2018

DOI: 10.1017/JFM.2018.508

Abstract: Fully resolved measurements of turbulent boundary layers are reported for the Reynolds number range $Re_{\\unicode[STIX]{x1D70F}}=6000{-}20\\,000$ . Despite several decades of research in wall-bounded turbulence there is still controversy over the behaviour of streamwise turbulence intensities near the wall, especially at high Reynolds numbers. Much of it stems from the uncertainty in measurement due to finite spatial resolution. Conventional hot-wire anemometry is limited for high Reynolds number measurements due to limited spatial resolution issues that cause attenuation in the streamwise turbulence intensity profile near the wall. To address this issue we use the nano-scale thermal anemometry probe (NSTAP), developed at Princeton University to conduct velocity measurements in the high Reynolds number boundary layer facility at the University of Melbourne. The NSTAP has a sensing length almost one order of magnitude smaller than conventional hot-wires. This enables us to acquire fully resolved velocity measurements of turbulent boundary layers up to $Re_{\\unicode[STIX]{x1D70F}}=20\\,000$ . Results show that in the near-wall region, the viscous-scaled streamwise turbulence intensity grows with $Re_{\\unicode[STIX]{x1D70F}}$ in the Reynolds number range of the experiments. A second outer peak in the streamwise turbulence intensity is also shown to emerge at the highest Reynolds numbers. Moreover, the energy spectra in the near-wall region show excellent inner scaling over the small to moderate wavelength range, followed by a large-scale influence that increases with Reynolds number. Outer scaling in the outer region is found to collapse the energy spectra over high wavelengths across various Reynolds numbers.

Turbulent drag reduction by spanwise wall forcing.

Publisher: Cambridge University Press (CUP)

Date: 28-07-2023

DOI: 10.1017/JFM.2023.499

Abstract: Turbulent drag reduction (DR) through streamwise travelling waves of the spanwise wall oscillation is investigated over a wide range of Reynolds numbers. Here, in Part 1, wall-resolved large-eddy simulations in a channel flow are conducted to examine how the frequency and wavenumber of the travelling wave influence the DR at friction Reynolds numbers $Re_\\tau = 951$ and $4000$ . The actuation parameter space is restricted to the inner-scaled actuation (ISA) pathway, where DR is achieved through direct attenuation of the near-wall scales. The level of turbulence attenuation, hence DR, is found to change with the near-wall Stokes layer protrusion height $\\ell _{0.01}$ . A range of frequencies is identified where the Stokes layer attenuates turbulence, lifting up the cycle of turbulence generation and thickening the viscous sublayer in this range, the DR increases as $\\ell _{0.01}$ increases up to $30$ viscous units. Outside this range, the strong Stokes shear strain enhances near-wall turbulence generation leading to a drop in DR with increasing $\\ell _{0.01}$ . We further find that, within our parameter and Reynolds number space, the ISA pathway has a power cost that always exceeds any DR savings. This motivates the study of the outer-scaled actuation pathway in Part 2, where DR is achieved through actuating the outer-scaled motions.

Data-driven enhancement of coherent structure-based models for predicting instantaneous wall turbulence

Publisher: Elsevier BV

Date: 12-2021

DOI: 10.1016/J.IJHEATFLUIDFLOW.2021.108879

Ensuring Best Practice in Genomic Education and Evaluation: A Program Logic Approach

Publisher: Frontiers Media SA

Date: 08-11-2019

DOI: 10.3389/FGENE.2019.01057

Simultaneous skin friction and velocity measurements in high Reynolds number pipe and boundary layer flows

Publisher: Cambridge University Press (CUP)

Date: 21-05-2019

DOI: 10.1017/JFM.2019.303

Abstract: Streamwise velocity and wall-shear stress are acquired simultaneously with a hot-wire and an array of azimuthal/spanwise-spaced skin friction sensors in large-scale pipe and boundary layer flow facilities at high Reynolds numbers. These allow for a correlation analysis on a per-scale basis between the velocity and reference skin friction signals to reveal which velocity-based turbulent motions are stochastically coherent with turbulent skin friction. In the logarithmic region, the wall-attached structures in both the pipe and boundary layers show evidence of self-similarity, and the range of scales over which the self-similarity is observed decreases with an increasing azimuthal/spanwise offset between the velocity and the reference skin friction signals. The present empirical observations support the existence of a self-similar range of wall-attached turbulence, which in turn are used to extend the model of Baars et al. ( J. Fluid Mech. , vol. 823, p. R2) to include the azimuthal/spanwise trends. Furthermore, the region where the self-similarity is observed correspond with the wall height where the mean momentum equation formally admits a self-similar invariant form, and simultaneously where the mean and variance profiles of the streamwise velocity exhibit logarithmic dependence. The experimental observations suggest that the self-similar wall-attached structures follow an aspect ratio of $7:1:1$ in the streamwise, spanwise and wall-normal directions, respectively.

Scaling of the turbulent/non-turbulent interface in boundary layers

Publisher: Cambridge University Press (CUP)

Date: 19-06-2014

DOI: 10.1017/JFM.2014.298

Abstract: Scaling of the interface that demarcates a turbulent boundary layer from the non-turbulent free stream is sought using theoretical reasoning and experimental evidence in a zero-pressure-gradient boundary layer. The data-analysis, utilising particle image velocimetry (PIV) measurements at four different Reynolds numbers ( $\\def \\xmlpi #1{}\\def \\mathsfbi #1{\\boldsymbol {\\mathsf {#1}}}\\let \\le =\\leqslant \\let \\leq =\\leqslant \\let \\ge =\\geqslant \\let \\geq =\\geqslant \\def \\Pr {\\mathit {Pr}}\\def \\Fr {\\mathit {Fr}}\\def \\Rey {\\mathit {Re}}\\delta u_{\\tau }/\\nu =1200\\mbox{--}14\\, 500$ ), indicates the presence of a viscosity dominated interface at all Reynolds numbers. It is found that the mean normal velocity across the interface and the tangential velocity jump scale with the skin-friction velocity $u_{\\tau }$ and are approximately $u_{\\tau }/10$ and $u_{\\tau }$ , respectively. The width of the superlayer is characterised by the local vorticity thickness $\\delta _{\\omega }$ and scales with the viscous length scale $\\nu /u_{\\tau }$ . An order of magnitude analysis of the tangential momentum balance within the superlayer suggests that the turbulent motions also scale with inner velocity and length scales $u_{\\tau }$ and $\\nu /u_{\\tau }$ , respectively. The influence of the wall on the dynamics in the superlayer is considered via Townsend’s similarity hypothesis, which can be extended to account for the viscous influence at the turbulent/non-turbulent interface. Similar to a turbulent far-wake the turbulent motions in the superlayer are of the same order as the mean velocity deficit, which lends to a physical explanation for the emergence of the wake profile in the outer part of the boundary layer.

Self-similarity of the large-scale motions in turbulent pipe flow

Publisher: Cambridge University Press (CUP)

Date: 02-03-2016

DOI: 10.1017/JFM.2016.100

Abstract: Townsend’s attached eddy hypothesis assumes the existence of a set of energetic and geometrically self-similar eddies in the logarithmic layer in wall-bounded turbulent flows, which can be scaled with their distance to the wall. To examine the possible self-similarity of the energetic eddies in fully developed turbulent pipe flow, we performed stereo particle image velocimetry measurements together with a proper orthogonal decomposition analysis. For two Reynolds numbers, $Re_{{\\it\\tau}}=1330$ and 2460, the resulting modes/eddies were shown to exhibit self-similar behaviour for eddies with wall-normal length scales spanning a decade. This single length scale provides a complete description of the cross-sectional shape of the self-similar eddies.

Inclined cross-stream stereo particle image velocimetry measurements in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 11-10-2005

DOI: 10.1017/S0022112005005872

Assessment of a miniature four-roll mill and a cross-slot microchannel for high-strain-rate stagnation point flows

Publisher: IOP Publishing

Date: 14-03-2018

DOI: 10.1088/1361-6501/AAACF3

Streamwise inclination angle of large wall-attached structures in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 02-09-2019

DOI: 10.1017/JFM.2019.663

Abstract: The streamwise inclination angle of large wall-attached structures, in the log region of a canonical turbulent boundary layer, is estimated via spectral coherence analysis, and is found to be approximately $45^{\\circ }$ . This is consistent with assumptions used in prior attached eddy model-based simulations. Given that the inclination angle obtained via standard two-point correlations is influenced by the range of scales in the turbulent flow (Marusic, Phys. Fluids , vol. 13 (3), 2001, pp. 735–743), the present result is obtained by isolating the large wall-attached structures from the rest of the turbulence. This is achieved by introducing a spanwise offset between two hot-wire probes, synchronously measuring the streamwise velocity at a near-wall and log-region reference location, to assess the wall coherence. The methodology is shown to be effective by applying it to data sets across Reynolds numbers, $Re_{\\unicode[STIX]{x1D70F}}\\sim O(10^{3})$ – $O(10^{6})$ .

Australian human research ethics committee members’ confidence in reviewing genomic research applications

Publisher: Springer Science and Business Media LLC

Date: 26-08-2021

DOI: 10.1038/S41431-021-00951-5

Skin-friction drag reduction in a high-Reynolds-number turbulent boundary layer via real-time control of large-scale structures

Publisher: Elsevier BV

Date: 10-2017

DOI: 10.1016/J.IJHEATFLUIDFLOW.2017.05.003

Modelling and operation of sub-miniature constant temperature hot-wire anemometry

Publisher: IOP Publishing

Date: 21-10-2016

DOI: 10.1088/0957-0233/27/12/125301

Large-scale influences in near-wall turbulence

Publisher: The Royal Society

Date: 18-01-2007

DOI: 10.1098/RSTA.2006.1942

Abstract: Hot-wire data acquired in a high Reynolds number facility are used to illustrate the need for adequate scale separation when considering the coherent structure in wall-bounded turbulence. It is found that a large-scale motion in the log region becomes increasingly comparable in energy to the near-wall cycle as the Reynolds number increases. Through decomposition of fluctuating velocity signals, it is shown that this large-scale motion has a distinct modulating influence on the small-scale energy (akin to litude modulation). Reassessment of DNS data, in light of these results, shows similar trends, with the rate and intensity of production due to the near-wall cycle subject to a modulating influence from the largest-scale motions.

Investigation of large-scale coherence in a turbulent boundary layer using two-point correlations

Publisher: Cambridge University Press (CUP)

Date: 10-02-2005

DOI: 10.1017/S0022112004002277

Trajectory of a synthetic jet issuing into high-Reynolds-number turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 05-10-2018

DOI: 10.1017/JFM.2018.734

Abstract: Synthetic jets are zero-net-mass-flux actuators that can be used in a range of flow control applications. For some applications, the scaling of the trajectory of the jet with actuation and cross-flow parameters is important. This scaling is investigated for changes in the friction Reynolds number, changes in the velocity ratio (defined as the ratio between the mean jet blowing velocity and the free-stream velocity) and changes in the actuation frequency of the jet. A distinctive aspect of this study is the high-Reynolds-number turbulent boundary layers (up to $Re_{\\unicode[STIX]{x1D70F}}=12\\,800$ ) of the cross-flow. To our knowledge, this is the first study to investigate the effect of the friction Reynolds number of the cross-flow on the trajectory of an (unsteady) jet, as well as the first study to systematically investigate the scaling of the trajectory with actuation frequency. A broad range of parameters is varied (rather than an in-depth investigation of a single parameter) and the results of this study are meant to indicate the relative importance of each parameter rather than the exact influence on the trajectory. Within the range of parameters explored, the critical ones are found to be the velocity ratio as well as a non-dimensional frequency based on the jet actuation frequency, the cross-flow velocity and the jet dimensions. The Reynolds number of the boundary layer is shown to have only a small effect on the trajectory. An expression for the trajectory of the jet is derived from the data, which (in the limit) is consistent with known expressions for the trajectory of a steady jet in a cross-flow.

Characterisation of hydrodynamic trapping in microfluidic cross-slot devices for high strain rate applications

Publisher: Royal Society of Chemistry (RSC)

Date: 2023

DOI: 10.1039/D3LC00256J

Abstract: The maximum strain rate at the stagnation point of the cross-slot channel relies on the control algorithm's time-delay and pixel resolution. This framework holds great potential for carrying out single cell analysis, as demonstrated in this study.

Universal aspects of small-scale motions in turbulence

Publisher: Cambridge University Press (CUP)

Date: 22-09-2010

DOI: 10.1017/S0022112010003381

Abstract: Two aspects of small-scale turbulence are currently regarded universal, as they have been reported for a wide variety of turbulent flows. Firstly, the vorticity vector has been found to display a preferential alignment with the eigenvector corresponding to the intermediate eigenvalue of the strain rate tensor and secondly, the joint probability density function (p.d.f.) of the second and third invariant of the velocity gradient tensor, Q and R , has a characteristic teardrop shape. This paper provides an explanation for these universal aspects in terms of a spatial organization of coherent structures, which is based on an evaluation of the average flow pattern in the local coordinate system defined by the eigenvectors of the strain rate tensor. The approach contrasts with previous investigations, which have relied on assumed model flows. The present average flow patterns have been calculated for existing experimental (particle image velocimetry) or numerical (direct numerical simulation) datasets of a turbulent boundary layer (TBL), a turbulent channel flow and for homogeneous isotropic turbulence. All results show a shear-layer structure consisting of aligned vortical motions, separating two larger-scale regions of relatively uniform flow. Because the directions of maximum and minimum strain in a shear layer are in the plane normal to the vorticity vector, this vector aligns with the remaining strain direction, i.e. the intermediate eigenvector of the strain rate tensor. Further, the QR joint p.d.f. for these average flow patterns reveals a shape reminiscent of the teardrop, as seen in many turbulent flows. The above-mentioned organization of the small-scale motions is not only found in the average patterns, but is also frequently observed in the instantaneous velocity fields of the different turbulent flows. It may, therefore, be considered relevant and universal.

Effective diffusivity and mass flux across the sediment‐water interface in streams

Publisher: American Geophysical Union (AGU)

Date: 05-2012

DOI: 10.1029/2011WR011148

Controlling the Large-Scale Motions in a Turbulent Boundary Layer

Publisher: Springer Berlin Heidelberg

Date: 13-11-2013

DOI: 10.1007/978-3-642-40371-2_2

Towards Reconciling the Large-Scale Structure of Turbulent Boundary Layers in the Atmosphere and Laboratory

Publisher: Springer Science and Business Media LLC

Date: 02-06-2012

DOI: 10.1007/S10546-012-9735-4

The influence of pipe length on turbulence statistics computed from direct numerical simulation data

Publisher: AIP Publishing

Date: 11-2010

DOI: 10.1063/1.3489528

Abstract: In this paper, direct numerical simulation of fully developed turbulent pipe flow is carried out at Reτ≈170 and 500 to investigate the effect of the streamwise periodic length on the convergence of turbulence statistics. Mean flow, turbulence intensities, correlations, and energy spectra were computed. The findings show that in the near-wall region (below the buffer region, r+≤30), the required pipe length for all turbulence statistics to converge needs to be at least a viscous length of O(6300) wall units and should not be scaled with the pipe radius (δ). It was also found for convergence of turbulence statistics at the outer region that the pipe length has to be scaled with pipe radius and a proposed pipe length of 8πδ seems sufficient for the Reynolds numbers considered in this study.

Navier-Stokes–based linear model for unstably stratified turbulent channel flows

Publisher: American Physical Society (APS)

Date: 06-04-2022

DOI: 10.1103/PHYSREVFLUIDS.7.044601

Entrainment at multi-scales across the turbulent/non-turbulent interface in an axisymmetric jet

Publisher: Cambridge University Press (CUP)

Date: 10-08-2016

DOI: 10.1017/JFM.2016.474

Abstract: We consider the scaling of the mass flux and entrainment velocity across the turbulent/non-turbulent interface (TNTI) in the far field of an axisymmetric jet at high Reynolds number. Time-resolved, simultaneous multi-scale particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) are used to identify and track the TNTI, and directly measure the local entrainment velocity along it. Application of box-counting and spatial-filtering methods, with filter sizes $\\unicode[STIX]{x1D6E5}$ spanning over two decades in length, show that the mean length of the TNTI exhibits a power-law behaviour with a fractal dimension $D\\approx 0.31{-}0.33$ . More importantly, we invoke a multi-scale methodology to confirm that the mean mass flux, which is equal to the product of the entrainment velocity and the surface area, remains constant across the range of filter sizes. The results, within experimental uncertainty, also show that the entrainment velocity along the TNTI exhibits a power-law behaviour with $\\unicode[STIX]{x1D6E5}$ , such that the entrainment velocity increases with increasing $\\unicode[STIX]{x1D6E5}$ . In fact, the mean entrainment velocity scales at a rate that balances the scaling of the TNTI length such that the mass flux remains independent of the coarse-grain filter size, as first suggested by Meneveau & Sreenivasan ( Phys. Rev. A, vol. 41, no. 4, 1990, pp. 2246–2248). Hence, at the smallest scales the entrainment velocity is small but is balanced by the presence of a very large surface area, whilst at the largest scales the entrainment velocity is large but is balanced by a smaller (smoother) surface area.

Uniform momentum zones in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 02-12-2015

DOI: 10.1017/JFM.2015.672

Abstract: Structural properties of regions of uniform streamwise momentum in turbulent boundary layers are examined using experimental databases obtained from particle image velocimetry. This investigation employs a large range of Reynolds numbers, spanning more than an order of magnitude ( $Re_{{\\it\\tau}}=10^{3}{-}10^{4}$ ), enabling us to provide a detailed description of uniform momentum zones as a function of Reynolds number. Our analysis starts by examining the identification criterion used by Adrian et al. ( J. Fluid Mech. , vol. 422, 2000, pp. 1–54) to report the presence of uniform momentum zones in turbulent boundary layers. This criterion is then applied to show that a zonal-like structural arrangement is prevalent in all datasets examined, emphasising its importance in the structural organisation. Streamwise velocity fluctuations within the zones are observed to be small but they are bounded by distinct step changes in streamwise momentum which indicate that shear layers of intense vorticity separate each zone. A log-linear increase in the number of these zones with increasing Reynolds number is revealed, together with an increase in the thicknesses of zones with increasing distance from the wall. These results support a hierarchical length-scale distribution of coherent structures, which generate zonal-like organisation within turbulent boundary layers. Interpretation of these findings is aided by employing synthetic velocity fields generated using a model based on the attached eddy hypothesis, which is described in the work of Perry and co-workers. Comparisons between the model and experimental results show that a hierarchy of self-similar structures leads to population densities and length-scale distributions of uniform momentum zones that closely adhere to those observed experimentally in this study.

Hydraulic resistance in open-channel flows over self-affine rough beds

Publisher: Informa UK Limited

Date: 04-07-2019

DOI: 10.1080/00221686.2018.1473296

Periodicity of large-scale coherence in turbulent boundary layers

Publisher: Elsevier BV

Date: 06-2020

DOI: 10.1016/J.IJHEATFLUIDFLOW.2020.108575

Large-scale amplitude modulation of the small-scale structures in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 06-2009

DOI: 10.1017/S0022112009006946

Abstract: In this paper we investigate the relationship between the large- and small-scale energy-containing motions in wall turbulence. Recent studies in a high-Reynolds-number turbulent boundary layer (Hutchins & Marusic, Phil. Trans. R. Soc. Lond . A, vol. 365, 2007 a , pp. 647–664) have revealed a possible influence of the large-scale boundary-layer motions on the small-scale near-wall cycle, akin to a pure litude modulation. In the present study we build upon these observations, using the Hilbert transformation applied to the spectrally filtered small-scale component of fluctuating velocity signals, in order to quantify the interaction. In addition to the large-scale log-region structures superimposing a footprint (or mean shift) on the near-wall fluctuations (Townsend, The Structure of Turbulent Shear Flow , 2nd edn., 1976, Cambridge University Press Metzger & Klewicki, Phys. Fluids , vol. 13, 2001, pp. 692–701.), we find strong supporting evidence that the small-scale structures are subject to a high degree of litude modulation seemingly originating from the much larger scales that inhabit the log region. An analysis of the Reynolds number dependence reveals that the litude modulation effect becomes progressively stronger as the Reynolds number increases. This is demonstrated through three orders of magnitude in Reynolds number, from laboratory experiments at Re τ ~ 10 3 –10 4 to atmospheric surface layer measurements at Re τ ~ 10 6 .

Use of eddy viscosity in resolvent analysis of turbulent channel flow

Publisher: American Physical Society (APS)

Date: 06-2023

DOI: 10.1103/PHYSREVFLUIDS.8.064601

Wall-bounded turbulent flows at high Reynolds numbers: Recent advances and key issues

Publisher: AIP Publishing

Date: 06-2010

DOI: 10.1063/1.3453711

Abstract: Wall-bounded turbulent flows at high Reynolds numbers have become an increasingly active area of research in recent years. Many challenges remain in theory, scaling, physical understanding, experimental techniques, and numerical simulations. In this paper we distill the salient advances of recent origin, particularly those that challenge textbook orthodoxy. Some of the outstanding questions, such as the extent of the logarithmic overlap layer, the universality or otherwise of the principal model parameters such as the von Kármán “constant,” the parametrization of roughness effects, and the scaling of mean flow and Reynolds stresses, are highlighted. Research avenues that may provide answers to these questions, notably the improvement of measuring techniques and the construction of new facilities, are identified. We also highlight aspects where differences of opinion persist, with the expectation that this discussion might mark the beginning of their resolution.

Characteristics of vortex packets in turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 10-03-2003

DOI: 10.1017/S0022112002003270

Abstract: Stereoscopic particle image velocimetry (PIV) was used to measure all three instantaneous components of the velocity field in streamwise–spanwise planes of a turbulent boundary layer at Re τ =1060 ( Re θ =2500). Datasets were obtained in the logarithmic layer and beyond. The vector fields in the log layer ( z + =92 and 150) revealed signatures of vortex packets similar to those proposed by Adrian and co-workers in their PIV experiments. Groups of legs of hairpin vortices appeared to be coherently arranged in the streamwise direction. These regions also generated substantial Reynolds shear stress, sometimes as high as 40 times − uw . A feature extraction algorithm was developed to automate the identification and characterization of these packets of hairpin vortices. Identified patches contributed 28% to − uw while occupying only 4% of the total area at z + =92. At z + =150, these patches occupied 4.5% of the total area while contributing 25% to − uw . Beyond the log layer ( z + =198 and 530), the spatial organization into packets is seen to break down.

Laminar and turbulent comparisons for channel flow and flow control

Publisher: Cambridge University Press (CUP)

Date: 03-01-2007

DOI: 10.1017/S0022112006003247

Abstract: A formula is derived that shows exactly how much the discrepancy between the volume flux in laminar and in turbulent flow at the same pressure gradient increases as the pressure gradient is increased. We compare laminar and turbulent flows in channels with and without flow control. For the related problem of a fixed bulk-Reynolds-number flow, we seek the theoretical lowest bound for skin-friction drag for control schemes that use surface blowing and suction with zero-net volume-flux addition. For one such case, using a crossflow approach, we show that sustained drag below that of the laminar-Poiseuille-flow case is not possible. For more general control strategies we derive a criterion for achieving sublaminar drag and use this to consider the implications for control strategy design and the limitations at high Reynolds numbers.

Age and growth in the Australian freshwater mussel, Westralunio carteri, with an evaluation of the fluorochrome calcein for validating the assumption of annulus formation

Publisher: University of Chicago Press

Date: 12-2014

DOI: 10.1086/677815

Range decline and conservation status of Westralunio carteri Iredale, 1934 (Bivalvia:Hyriidae) from south-western Australia

Publisher: CSIRO Publishing

Date: 2015

DOI: 10.1071/ZO15002

Abstract: Westralunio carteri is the only species of freshwater mussel found in south-western Australia and, owing to a lack of comprehensive information on its ecology, its conservation status has been speculative. To more accurately predict the true conservation status of this species, the historical and contemporary distributional records were modelled with environmental data that identified salinity, perenniality and total nitrogen as variables responsible for limiting the species’ current extent of occurrence, inferring threatening processes. The species was found to have undergone a 49% reduction in extent of occurrence in less than three generations, due primarily to secondary salinisation. Current distribution is bounded by Gingin Brook in the north to the Kent, Goodga and Waychinicup Rivers in the South, within 50–100 km of coastal south-western Australia. Field observations indicated that W. carteri was almost never found at sites where mean salinity was .6 g L–1. This was corroborated by laboratory tolerance trials that showed that W. carteri has an acute salinity tolerance (LD50) of 1.6–3.0 g L–1. Application of IUCN Red List criteria indicates that W. carteri qualifies for listing as vulnerable. Conservation management measures should focus on maintaining existing populations.

Spectral stochastic estimation of high-Reynolds-number wall-bounded turbulence for a refined inner-outer interaction model

Publisher: American Physical Society (APS)

Date: 23-09-2016

DOI: 10.1103/PHYSREVFLUIDS.1.054406

Self-similarity of wall-attached turbulence in boundary layers

Publisher: Cambridge University Press (CUP)

Date: 15-06-2017

DOI: 10.1017/JFM.2017.357

Abstract: An assessment of the turbulent boundary layer flow structure, which is coherent with the near-wall region, is carried out through a spectral coherence analysis. This spectral method is applied to datasets comprising synchronized two-point streamwise velocity signals at a near-wall reference position and a range of wall-normal positions spanning a Reynolds-number range $Re_{\\unicode[STIX]{x1D70F}}\\sim O(10^{3}){-}O(10^{6})$ . Within each dataset, a self-similar structure is identified from the coherence between the turbulence in the logarithmic region and at the near-wall reference position. This self-similarity is described by a streamwise/wall-normal aspect ratio of $\\unicode[STIX]{x1D706}_{x}/z\\approx 14$ , where $\\unicode[STIX]{x1D706}_{x}$ and $z$ are the streamwise wavelength and wall-normal distance respectively.

Drag forces on a bed particle in open-channel flow: effects of pressure spatial fluctuations and very-large-scale motions

Publisher: Cambridge University Press (CUP)

Date: 25-01-2019

DOI: 10.1017/JFM.2018.1003

Abstract: The fluctuating drag forces acting on spherical roughness elements comprising the bed of an open-channel flow have been recorded along with synchronous measurements of the surrounding velocity field using stereoscopic particle image velocimetry. The protrusion of the target particle, equipped with a force sensor, was systematically varied between zero and one-half diameter relative to the hexagonally packed adjacent spheres. Premultiplied spectra of drag force fluctuations were found to have bimodal shapes with a low-frequency ( ${\\approx}0.5~\\text{Hz}$ ) peak corresponding to the presence of very-large-scale motions (VLSMs) in the turbulent flow. The high-frequency ( $\\gtrapprox 4~\\text{Hz}$ ) region of the drag force spectra cannot be explained by velocity time series extracted from points around the particle, but instead appears to be dominated by the action of pressure gradients in the overlying flow field. For small particle protrusions, this high-frequency region contributes a majority of the drag force variance, while the relative importance of the low-frequency drag force fluctuations increases with increasing protrusion. The litude of high-frequency drag force fluctuations is modulated by the VLSMs irrespective of particle protrusion. These results provide some insight into the mechanics of bed particle stability and indicate that the optimum conditions for particle entrainment may occur when a low-pressure region embedded in the high-velocity portion of a VLSM overlays a particle.

Two-dimensional energy spectra in high-Reynolds-number turbulent boundary layers

Publisher: Cambridge University Press (CUP)

Date: 02-08-2017

DOI: 10.1017/JFM.2017.359

Abstract: Here, we report the measurements of two-dimensional (2-D) spectra of the streamwise velocity ( $u$ ) in a high-Reynolds-number turbulent boundary layer. A novel experiment employing multiple hot-wire probes was carried out at friction Reynolds numbers ranging from 2400 to 26 000. Taylor’s frozen turbulence hypothesis is used to convert temporal-spanwise information into a 2-D spatial spectrum which shows the contribution of streamwise ( $\\unicode[STIX]{x1D706}_{x}$ ) and spanwise ( $\\unicode[STIX]{x1D706}_{y}$ ) length scales to the streamwise variance at a given wall height ( $z$ ). At low Reynolds numbers, the shape of the 2-D spectra at a constant energy level shows $\\unicode[STIX]{x1D706}_{y}/z\\sim (\\unicode[STIX]{x1D706}_{x}/z)^{1/2}$ behaviour at larger scales, which is in agreement with the existing literature at a matched Reynolds number obtained from direct numerical simulations. However, at high Reynolds numbers, it is observed that the square-root relationship tends towards a linear relationship ( $\\unicode[STIX]{x1D706}_{y}\\sim \\unicode[STIX]{x1D706}_{x}$ ), as required for self-similarity and predicted by the attached eddy hypothesis.

Enhancing Tomo-PIV reconstruction quality by reducing ghost particles

Publisher: IOP Publishing

Date: 20-12-2012

DOI: 10.1088/0957-0233/24/2/024010

Reynolds number and roughness effects on turbulent stresses in sandpaper roughness boundary layers

Publisher: American Physical Society (APS)

Date: 26-05-2017

DOI: 10.1103/PHYSREVFLUIDS.2.054608

Morphological and morphometrical description of the glochidia of Westralunio carteri Iredale, 1934 (Bivalvia: Unionoida: Hyriidae)

Publisher: Informa UK Limited

Date: 05-2013

DOI: 10.1080/13235818.2013.782791

Advances in three-dimensional coronary imaging and computational fluid dynamics

Publisher: Ovid Technologies (Wolters Kluwer Health)

Date: 08-2015

DOI: 10.1097/MCA.0000000000000219

Coherent structures in flow over hydraulic engineering surfaces

Publisher: Informa UK Limited

Date: 10-2012

DOI: 10.1080/00221686.2012.729540

Revisiting end conduction effects in constant temperature hot-wire anemometry

Publisher: Springer Science and Business Media LLC

Date: 04-08-2018

DOI: 10.1007/S00348-018-2587-Z

Near wall coherence in wall-bounded flows and implications for flow control

Publisher: Elsevier BV

Date: 12-2020

DOI: 10.1016/J.IJHEATFLUIDFLOW.2020.108683

Spatial resolution correction for wall-bounded turbulence measurements

Publisher: Cambridge University Press (CUP)

Date: 06-04-2011

DOI: 10.1017/JFM.2011.19

Abstract: A correction for streamwise Reynolds stress data acquired with insufficient spatial resolution is proposed for wall-bounded flows. The method is based on the attached eddy hypothesis to account for spatial filtering effects at all wall-normal positions. This analysis reveals that outside the near-wall region the spatial filtering effect scales inversely with the distance from the wall, in contrast to the commonly assumed scaling with the viscous length scale. The new formulation is shown to work very well for data taken over a wide range of Reynolds numbers and wire lengths.

An investigation of channel flow with a smooth air–water interface

Publisher: Springer Science and Business Media LLC

Date: 06-2015

DOI: 10.1007/S00348-015-1985-8

Investigation of cold-wire spatial and temporal resolution issues in thermal turbulent boundary layers

Publisher: Elsevier BV

Date: 04-2022

DOI: 10.1016/J.IJHEATFLUIDFLOW.2022.108926

A calibration technique to correct sensor drift issues in hot-wire anemometry

Publisher: IOP Publishing

Date: 15-09-2014

DOI: 10.1088/0957-0233/25/10/105304

Measurements from flame chemiluminescence tomography of forced laminar premixed propane flames

Publisher: Elsevier BV

Date: 09-2017

DOI: 10.1016/J.COMBUSTFLAME.2017.05.003

Active Micropump-Mixer for Rapid Antiplatelet Drug Screening in Whole Blood

Publisher: American Chemical Society (ACS)

Date: 25-07-2019

DOI: 10.1021/ACS.ANALCHEM.9B02486

Abstract: There is a need for scalable automated lab-on-chip systems incorporating precise hemodynamic control that can be applied to high-content screening of new more efficacious antiplatelet therapies. This paper reports on the development and characterization of a novel active micropump-mixer microfluidic to address this need. Using a novel reciprocating elastomeric micropump design, we take advantage of the flexible structural and actuation properties of this framework to manage the hemodynamics for on-chip platelet thrombosis assay on type 1 fibrillar collagen, using whole blood. By characterizing and harnessing the complex three-dimensional hemodynamics of the micropump operation in conjunction with a microvalve controlled reagent injection system we demonstrate that this prototype can act as a real-time assay of antiplatelet drug pharmacokinetics. In a proof-of-concept preclinical application, we utilize this system to investigate the way in which rapid dosing of human whole blood with isoform selective inhibitors of phosphatidylinositol 3-kinase dose dependently modulate platelet thrombus dynamics. This modular system exhibits utility as an automated multiplexable assay system with applications to high-content chemical library screening of new antiplatelet therapies.

Fractal scaling of the turbulence interface in gravity currents

Publisher: Cambridge University Press (CUP)

Date: 09-05-2017

DOI: 10.1017/JFM.2017.245

Abstract: It was previously observed by Krug et al. ( J. Fluid Mech. , vol. 765, 2015, pp. 303–324) that the surface area $A_{\\unicode[STIX]{x1D702}}$ of the turbulent/non-turbulent interface (TNTI) in gravity currents decreases with increasing stratification, significantly reducing the entrainment rate. Here, we consider the multiscale properties of this effect using direct numerical simulations of temporal gravity currents with different gradient Richardson numbers $Ri_{g}$ . Our results indicate that the reduction of $A_{\\unicode[STIX]{x1D702}}$ is caused by a decrease of the fractal scaling exponent $\\unicode[STIX]{x1D6FD}$ , while the scaling range remains largely unaffected. We further find that convolutions of the TNTI are characterized by different length scales in the streamwise and wall-normal directions, namely the integral scale $h$ and the shear scale $l_{Sk}=k^{1/2}/S$ (formed using the mean shear $S$ and the turbulent kinetic energy $k$ ) respectively. By recognizing that the anisotropy implied by the different scaling relations increases with increasing $Ri_{g}$ , we are able to model the $Ri_{g}$ dependence of $\\unicode[STIX]{x1D6FD}$ in good agreement with the data.

University Of Melbourne

Location: Australia

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University Of Minnesota

Location: United States of America

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University Of Minnesota

Location: No location found

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Linkage Projects - Grant ID: LP160100228

Start Date: 12-2016

End Date: 01-2020

Amount: $438,000.00

Funder: Australian Research Council

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End Date: 11-2017

Amount: $3,215,016.00

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Discovery Projects - Grant ID: DP130102307

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End Date: 12-2016

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Linkage Projects - Grant ID: LP150100233

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Funder: Australian Research Council

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Funder: Australian Research Council

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Funder: Australian Research Council

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Funder: Australian Research Council

Discovery Projects - Grant ID: DP0984577

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Funder: Australian Research Council

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Funder: Australian Research Council

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Amount: $500,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP100200090

Start Date: 03-2011

End Date: 01-2015

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Funder: Australian Research Council