ORCID Profile
0000-0002-2709-4321
Current Organisations
University of Melbourne
,
University of Adelaide
,
University of Leeds
,
University of Leeds School of Medicine
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Interdisciplinary Engineering | Turbulent Flows | Fluidisation and Fluid Mechanics
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Physical Sciences | Preparation of Brown Coal (Lignite) | Energy Conservation and Efficiency in Transport |
Related Links
Publications
Transient behaviour of decelerating turbulent pipe flows
Publisher: Cambridge University Press (CUP)
Date: 09-05-2023
DOI: 10.1017/JFM.2023.294
Abstract: This investigation characterises the time response and the transient turbulence dynamics undergone by rapidly decelerating turbulent pipe flows. A series of direct numerical simulations of decelerating flows between two steady Reynolds numbers were conducted for this purpose. The statistical analyses reveal that rapidly decelerating turbulent flows undergo four coherent, unambiguous transitional stages: inertial (stage I), a dramatic change of sign in the viscous force associated with the decay of the viscous shear stress at the wall together with a mild turbulence decay in the viscous sublayer friction recovery (stage II), a recovery in viscous force and progressive decay in the turbulent inertia at the near-wall region turbulence decay (stage III), a balanced decay in both turbulent inertia and viscous force at the near-wall and overlap regions core relaxation (stage IV), slow turbulence decay at the core region. The FIK identity derived by Fukagata, Iwamoto and Kasagi ( Phys. Fluids , vol. 14, 2002, L73–L76) was used to understand further how the flow dynamics influence the time response of the skin friction coefficient ( $C_f$ ). The results show that although $C_f$ plateaus during the fourth stage, the turbulent contribution keeps decaying, undershoots and finally recovers to attain its final steady value. The time evolution of the azimuthal vorticity ( $\\omega _\\theta$ ) flux reveals that as the flow is decelerated, a layer of negative $\\omega _\\theta$ is produced at the wall during the flow excursion. As time progresses, this negative vorticity propagates in the wall-normal direction, attenuating the pre-existing vorticity and producing a decay in the turbulence levels.
Numerical and experimental investigations of the flow–pressure relation in multiple sequential stenoses coronary artery
Publisher: Springer Science and Business Media LLC
Date: 20-02-2017
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
Turbulent pipe flow at Reτ ≈ 1000 : A comparison of wall-resolved large-eddy simulation, direct numerical simulation and hot-wire experiment
Publisher: Elsevier BV
Date: 11-2015
On the effect of streamwise and spanwise spacing to height ratios of three-dimensional sinusoidal roughness on turbulent boundary layers
Publisher: AIP Publishing
Date: 02-2023
DOI: 10.1063/5.0136072
Abstract: A developing zero pressure gradient (ZPG) turbulent boundary layer (TBL) over different three-dimensional (3D) sinewave roughnesses is investigated experimentally using single hot-wire anemometry. Seven different sinewave profiles are fabricated with the same litude and with different wavelengths in the streamwise (sx) and spanwise (sz) directions. The effects of varying sx and sz on turbulence statistics and the drag coefficient (Cf) are assessed. The wall-unit normalized streamwise mean velocity profile is shifted downward compared with the smooth wall profile for all roughnesses. The streamwise spacing to height ratio sx/k has a more significant effect on the roughness function ΔU+ and Cf compared with the spanwise spacing to height ratio sz/k. However, sz/k has a large impact on the streamwise turbulence intensities in the log and outer layer. An excellent collapse is observed among the mean streamwise velocity profiles plotted in defect form in the outer region. However, a lack of similarity between TBLs over different rough surfaces is observed in the outer region for the turbulence intensities profiles. For isotropic 3D sinusoidal roughness (equal streamwise and spanwise spacing to height ratios), the contours of premultiplied streamwise turbulent energy spectrograms show an increase in energy in the outer layer with increasing spacing to height ratios. For anisotropic 3D sinusoidal roughness (unequal streamwise and spanwise spacing to height ratios), the contours of premultiplied streamwise turbulent energy spectrograms show an increase in energy in the outer layer with increasing sz/sx from half to two in this study.
Influence of skewed three-dimensional sinusoidal surface roughness on turbulent boundary layers
Publisher: AIP Publishing
Date: 05-2023
DOI: 10.1063/5.0152391
Abstract: The impact of roughness skewness (ksk) on turbulent boundary layer (TBL) flow with a zero pressure gradient over three-dimensional (3D) sinusoidal rough surfaces was experimentally investigated using a single hotwire anemometer. Nine 3D sinusoidal profiles were manufactured with positive, negative, and zero roughness skewness values. Measurements were taken at three different freestream velocities for each surface and compared with smooth wall TBL results. This study covered a range of friction Reynolds numbers (Reτ) from approximately 1000 to 4000, with δ/k≈20 ± 2, where δ represents the local boundary layer thickness, and k is the maximum height of the roughness, measured from the valley to peak. The results indicate that the wall-unit normalized streamwise mean velocity profiles for all rough surfaces exhibit a downward shift compared to the smooth wall profiles. Surfaces with positive roughness skewness produced the highest drag, leading to the largest downward shift. The friction coefficient (Cf) decreased as ksk decreased. The percentage increase in Cf and ΔU+ (the roughness function) was much larger when moving from negative to zero roughness skewness than when moving from zero to positive roughness skewness. The small differences in turbulence intensity profiles and higher-order turbulence statistics in the outer region of the TBL support the outer layer similarity hypothesis for the roughness considered in this study. The autocorrelation study revealed that surfaces with positive roughness skewness tend to shorten the average length of turbulence structures in the near-wall region.
Attenuation of turbulence by the passive control of sweep events in a turbulent boundary layer using micro-cavities
Publisher: AIP Publishing
Date: 11-2017
DOI: 10.1063/1.4995466
Abstract: Cavity arrays have been previously identified to disrupt the sweep events and consequently the bursting cycle in the boundary layer by capturing the structures responsible for the Reynolds stresses. In the present study, the sensitivity of a flushed-surface cavity array in reducing the turbulent energy production has been investigated. Two plates of varying thicknesses and four different backing cavity volumes were considered, at three different Reynolds numbers. The volume of the backing cavity was shown to be the most important characteristic in determining the attenuation of streamwise velocity fluctuations within the logarithmic region of the turbulent boundary layer. However, the results also demonstrated that the orifice length of the cavity array had negligible effect in modifying the reduction of the turbulent energy by the cavity array in this investigation. The results show that the maximum reduction in turbulence generation achieved for this study occurs when the backing volume is 3.1 × 106 times greater than the viscous length scale at Reθ = 3771. The reduction in turbulence intensity, sweep intensity, and energy spectrum were shown to be 5.6%, 6.3%, and 13.4%, respectively. By decreasing the cavity volume to zero, no change in the turbulent boundary layer turbulence statistics was found. The results suggest a larger reduction in turbulence intensity, sweep intensity, and energy spectrum that can be achieved with a larger backing volume.
Influence of a Large-Eddy-Breakup-Device on the Turbulent Interface of Boundary Layers
Publisher: Springer Science and Business Media LLC
Date: 18-10-2017
POD analysis of the turbulent boundary layer flow downstream of miniature vortex generators
Publisher: Elsevier BV
Date: 10-2023
Extreme wall shear stress events in turbulent pipe flows: spatial characteristics of coherent motions
Publisher: Cambridge University Press (CUP)
Date: 07-10-2020
DOI: 10.1017/JFM.2020.689
Performance Analysis of Novel Blade Design of Vertical Axis Wind Turbine
Publisher: IEEE
Date: 10-2019
Experimental characteristics and coupled nonlinear forced vibrations of axially travelling hyperelastic beams
Publisher: No publisher found
Date: 2022
The effect of nurse-to-patient ratios on nurse-sensitive patient outcomes in acute specialist units: a systematic review and meta-analysis
Publisher: Oxford University Press (OUP)
Date: 18-07-2017
Abstract: Nurses are pivotal in the provision of high quality care in acute hospitals. However, the optimal dosing of the number of nurses caring for patients remains elusive. In light of this, an updated review of the evidence on the effect of nurse staffing levels on patient outcomes is required. To undertake a systematic review and meta-analysis examining the association between nurse staffing levels and nurse-sensitive patient outcomes in acute specialist units. Nine electronic databases were searched for English articles published between 2006 and 2017. The primary outcomes were nurse-sensitive patient outcomes. Of 3429 unique articles identified, 35 met the inclusion criteria. All were cross-sectional and the majority utilised large administrative databases. Higher staffing levels were associated with reduced mortality, medication errors, ulcers, restraint use, infections, pneumonia, higher aspirin use and a greater number of patients receiving percutaneous coronary intervention within 90 minutes. A meta-analysis involving 175,755 patients, from six studies, admitted to the intensive care unit and/or cardiac/cardiothoracic units showed that a higher nurse staffing level decreased the risk of inhospital mortality by 14% (0.86, 95% confidence interval 0.79–0.94). However, the meta-analysis also showed high heterogeneity (I 2 =86%). Nurse-to-patient ratios influence many patient outcomes, most markedly inhospital mortality. More studies need to be conducted on the association of nurse-to-patient ratios with nurse-sensitive patient outcomes to offset the paucity and weaknesses of research in this area. This would provide further evidence for recommendations of optimal nurse-to-patient ratios in acute specialist units.
Systematic study of the Reynolds number and streamwise spacing effects in two-dimensional square-bar rough-wall turbulent boundary layers
Publisher: American Physical Society (APS)
Date: 10-01-2023
Flow topology of rare back flow events and critical points in turbulent channels and toroidal pipes
Publisher: IOP Publishing
Date: 04-2018
Vorticity Transport in Turbulent Pipe Flow
Publisher: The University of Queensland
Date: 11-12-2020
DOI: 10.14264/B2D6025
Large amplitude vibrations of imperfect porous-hyperelastic beams via a modified strain energy
Publisher: Elsevier BV
Date: 11-2021
An evaluation of the Minnesota Living with Heart Failure Questionnaire using Rasch analysis
Publisher: Springer Science and Business Media LLC
Date: 12-01-2014
DOI: 10.1007/S11136-013-0617-0
Abstract: The symptom burden of heart failure is significant and impacts upon health-related quality of life. The Minnesota Living with Heart Failure Questionnaire (MLHFQ) is widely used in clinical practice to measure self-reported health-related quality of life, but the psychometric properties of the instrument are not fully elucidated. To address this gap, we investigated item and person fit, differential item functioning, item thresholds ordering, targeting and dimensionality of the MLHFQ. Three approaches were used, exploratory factor analysis, Mokken analysis and Rasch analysis, on a convenience s le of 109 participants with a diagnosis of HF from the UK. Participants were typically male (67 %) with a mean age of 68 years (range 41-88). Findings from the exploratory factor analysis of the MLHFQ revealed three factors (physical, emotional and social) that explained 72 % of the total variance. Mokken analysis confirmed the MLHFQ total scale, and the three subscales, as valid ordinal scales: the total MLHFQ scale [overall Loevinger coefficient (H) = 0.61], physical scale (H = 0.75), emotional scale (H = 0.79) and social scale (H = 0.552). Rasch analysis confirmed the physical scale as a unidimensional scale, but this was not consistent for the total MLHFQ scale which showed poor fit to the Rasch model (χ (2) = 162), df = 42, p < 0.0001). Six items of the total scale were misfitting (7, 8, 10, 14-16) and removing them improved the fit of the total scale. The physical subscale showed fit to the Rasch model (χ (2) = 20.24, df = 16, p = 0.21), and there was evidence of unidimensionality (t tests = 0.09, lower bound 95 % CI 0.04). There was evidence of disordered thresholds for the MLHFQ total and physical scale, and targeting was poor for both the total scale and its subscales. We confirmed the MLHFQ subscales to be valid ordinal scales supporting the use of sum scores to assess quality of life in people diagnosed with HF. Floor effects were evident indicating that the ability of the instrument to identify differences across populations with mild HF may be suboptimal. The psychometric properties of the MLHFQ total scale may be improved by excluding problematic items from the total scale. Further research is warranted to verify findings from this study.
A numerical study of gravity effects on horizontal particle-laden pipe flows
Publisher: The University of Queensland
Date: 11-12-2020
DOI: 10.14264/8597E07
The skin-friction coefficient of a turbulent boundary layer modified by a large-eddy break-up device
Publisher: AIP Publishing
Date: 03-2021
DOI: 10.1063/5.0043984
Abstract: A computational study based on well-resolved large-eddy simulations is performed to study the skin friction modification by a large-eddy breakup device (LEBU) in a zero-pressure-gradient turbulent boundary layer. The LEBU was modeled using an immersed boundary method. It is observed that the presence of the device leads to the generation of wake vortices, which propagate downstream from the LEBU and toward the wall. A skin friction decomposition procedure is utilized to study different physical mechanisms of the observed skin friction reduction. From the skin friction decomposition, it is found that the skin friction reduction can be characterized by three universal regions of different changes for the skin friction contributions. The first region is predominantly associated with the formation of the wake vortices and the reduction of Reynolds shear stress. In the second region, the mean streamwise velocity fields show that a region of velocity deficit formed downstream of the LEBU propagates toward the wall and leads to turbulence reduction due to wake wall interactions, which also induces a local maximum skin friction reduction. In the third region, the dissipation of wake vortices leads to the regeneration of Reynolds shear stress. A quadrant analysis of the Reynolds shear stress contribution reveals that the LEBU increases the Q2 and Q4 contributions and attenuates the Q1 and Q3 contributions in the first region, followed by an onset of Reynolds shear stress further downstream.
Large-scale and small-scale contribution to the skin friction reduction in a modified turbulent boundary layer by a large-eddy break-up device
Publisher: American Physical Society (APS)
Date: 15-03-2022
Hemodynamics of stented coronary arteries: Experimental and numerical investigations
Publisher: The University of Queensland
Date: 11-12-2020
DOI: 10.14264/B68207F
Large eddy simulation and Reynolds-averaged Navier-Stokes calculations of supersonic impinging jets at varying nozzle-to-wall distances and impinging angles
Publisher: Elsevier BV
Date: 06-2014
Investigation of the flow structures in supersonic free and impinging jet flows
Publisher: ASME International
Date: 22-02-2013
DOI: 10.1115/1.4023190
Abstract: A numerical study of compressible jet flows is carried out using Reynolds averaged Navier–Stokes (RANS) turbulence models such as k-ɛ and k-ω-SST. An experimental investigation is performed concurrently using high-speed optical methods such as Schlieren photography and shadowgraphy. Numerical and experimental studies are carried out for the compressible impinging at various impinging angles and nozzle-to-wall distances. The results from both investigations converge remarkably well and agree with experimental data from the open literature. From the flow visualizations of the velocity fields, the RANS simulations accurately model the shock structures within the core jet region. The first shock cell is found to be constraint due to the interaction with the bow-shock structure for nozzle-to-wall distance less than 1.5 nozzle diameter. The results from the current study show that the RANS models utilized are suitable to simulate compressible free jets and impinging jet flows with varying impinging angles.
On Large-Scale Friction Control in Turbulent Wall Flow in Low Reynolds Number Channels
Publisher: Springer Science and Business Media LLC
Date: 12-03-2016
Characterisation of ethylene flames under a range of low-oxygen concentrations
Publisher: Elsevier BV
Date: 02-2023
Precursors of backflow events and their relationship with the near-wall self-sustaining process
Publisher: Cambridge University Press (CUP)
Date: 29-12-2022
Abstract: This study examines the precursors and consequences of rare backflow events at the wall using direct numerical simulation of turbulent pipe flow with a high spatiotemporal resolution. The results obtained from conditionally averaged fields reveal that the precursor of a backflow event is the asymmetric collision between a high- and a low-speed streak (LSS) associated with the sinuous mode of the streaks. As the collision occurs, a lifted shear layer with high local azimuthal enstrophy is formed at the trailing end of the LSS. Subsequently, a spanwise or an oblique vortex spontaneously arises. The dominant nonlinear mechanism by which this vortex is engendered is enstrophy intensification due to direct stretching of the lifted vorticity lines in the azimuthal direction. As time progresses, this vortex tilts and orientates towards the streamwise direction and, as its enstrophy increases, it induces the breakdown of the LSS located below it. Subsequently, this vortical structure advects as a quasi-streamwise vortex, as it tilts and stretches with time. As a result, it is shown that reverse flow events at the wall are the signature of the nonlinear mechanism of the self-sustaining process occurring at the near-wall region. Additionally, each backflow event has been tracked in space and time, showing that approximately 50 % of these events are followed by at least one additional vortex generation that gives rise to new backflow events. It is also found that up to a maximum of seven regenerations occur after a backflow event has appeared for the first time.
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
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.
Extension of the 1D Unsteady Friction Model for Rapidly Accelerating and Decelerating Turbulent Pipe Flows
Publisher: American Society of Civil Engineers (ASCE)
Date: 09-2022
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.
Endothelial shear stress 5 years after implantation of a coronary bioresorbable scaffold
Publisher: Oxford University Press (OUP)
Date: 02-02-2018
Abstract: As a sine qua non for arterial wall physiology, local hemodynamic forces such as endothelial shear stress (ESS) may influence long-term vessel changes as bioabsorbable scaffolds dissolve. The aim of this study was to perform serial computational fluid dynamic (CFD) simulations to examine immediate and long-term haemodynamic and vascular changes following bioresorbable scaffold placement. Coronary arterial models with long-term serial assessment (baseline and 5 years) were reconstructed through fusion of intravascular optical coherence tomography and angiography. Pulsatile non-Newtonian CFD simulations were performed to calculate the ESS and relative blood viscosity. Time-averaged, systolic, and diastolic results were compared between follow-ups. Seven patients (seven lesions) were included in this analysis. A marked heterogeneity in ESS and localised regions of high blood viscosity were observed post-implantation. Percent vessel area exposed to low averaged ESS (<1 Pa) significantly decreased over 5 years (15.92% vs. 4.99%, P 7 Pa) did not significantly change (moderate ESS: 76.93% vs. 80.7%, P = 0.546 high ESS: 7.15% vs. 14.31%, P = 0.281), leading to higher ESS at follow-up. A positive correlation was observed between baseline ESS and change in lumen area at 5 years (P < 0.0001). Maximum blood viscosity significantly decreased over 5 years (4.30 ± 1.54 vs. 3.21± 0.57, P = 0.028). Immediately after scaffold implantation, coronary arteries demonstrate an alternans of extremely low and high ESS values and localized areas of high blood viscosity. These initial local haemodynamic disturbances may trigger fibrin deposition and thrombosis. Also, low ESS can promote neointimal hyperplasia, but may also contribute to appropriate scaffold healing with normalisation of ESS and reduction in peak blood viscosity by 5 years.
Hydrodynamic simulation of submarine far field flow
Publisher: The University of Queensland
Date: 11-12-2020
DOI: 10.14264/343824B
Direct numerical simulation of low Reynolds number turbulent swirling pipe flows
Publisher: American Physical Society (APS)
Date: 25-11-2019
Turbulent Boundary Layer over various 2D Uniform Distributed Roughness Elements
Publisher: The University of Queensland
Date: 11-12-2020
DOI: 10.14264/B4A556C
Numerical simulation of two-stages contra-rotating vertical axis wind turbine
Publisher: The University of Queensland
Date: 11-12-2020
DOI: 10.14264/D1C920E
Interscale transport mechanisms in turbulent boundary layers
Publisher: Cambridge University Press (CUP)
Date: 28-06-2021
DOI: 10.1017/JFM.2021.504
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.
A Numerical Study of the Effects of the Velocity Ratio on Coflow Jet Characteristics
Publisher: ASME International
Date: 24-04-2020
DOI: 10.1115/1.4046769
Abstract: In this study, large eddy simulations (LES) of turbulent coflow jets are performed and designed to investigate the effects of the jet-to-coflow velocity ratio, Vr, on jet characteristics. A fully developed turbulent pipe flow at Re=10,000, based on the bulk velocity and pipe diameter, is employed as the jet outlet in this work. A comparison between laminar and turbulent jets is performed against the experimental results of a jet produced by a fully developed turbulent pipe flow. For the coflow jet, simulations with different jet-to-coflow velocity ratios (Vr = 3, 6, 12, and ∞) are performed to investigate the turbulence intensities and the decay of the centerline velocity of the jet. The results give two constant decay rates: Ku≈0.144 for single-phase jets and Ku≈0.133 for particle-laden jets. With a decrease in Vr (i.e., a higher coflow velocity), the results show a higher peak value and a larger droop rate for turbulence intensities. This study is then extended to investigate particle distribution under a two-way coupling regime, using a Lagrangian framework. The particle velocity and distribution along the jet centerline, and the particle clustering and radial probability distribution in the jet downstream domain are analyzed with the same coflow jet parameters. The particles tend to move faster and distribute preferentially in the center region with a decrease in Vr, which agrees with the increasing turbulence intensities along the jet centerline in the present work.
Spatial resolution correction for hot-wire anemometry in wall turbulence
Publisher: Springer Science and Business Media LLC
Date: 13-11-2010
Reynolds number effects in DNS of pipe flow and comparison with channels and boundary layers
Publisher: Elsevier BV
Date: 02-2014
Effect of artery curvature on the coronary fractional flow reserve
Publisher: AIP Publishing
Date: 03-2021
DOI: 10.1063/5.0042601
Abstract: Understanding the effect of the artery curvature on the pressure drop inside the arteries is of great importance due to the existence of several curved portions inside the coronary arterial system. In this paper, an experimental model is developed to account for the effect of the curvature of the coronary arteries on the pressure drop and Fractional Flow Reserve (FFR). FFR is an index for the evaluation of the functional significance of coronary stenosis and is defined as the ratio of the coronary pressure downstream of the stenosis to its upstream value. To measure the pressure drop and FFR across curved artery models, three-dimensional-printed curved artery models are fabricated and installed in the test section of the experimental rig. For ratios of curvature radius over the artery diameter ranging from 2 to 7, there are a minimum value for the pressure drop and, hence, a corresponding maximum value for FFR at a ratio of approximately 3. For the curved arteries with larger curvature radii, the pressure drop increases, and consequently, FFR decreases with an increase in the radius. The results showed that an accurate evaluation of the pressure drop and FFR inside a curved coronary artery can only be achieved by accounting for the effect of curvature parameters including the curvature angle and radius, such that neglecting the effect of the artery curvature results in an underestimation of the pressure drop by about 25%–35%. The developed equation is able to determine the pressure drop inside a curved coronary artery model noninvasively.
Mechanism of sweep event attenuation using micro-cavities in a turbulent boundary layer
Publisher: AIP Publishing
Date: 05-2018
DOI: 10.1063/1.5026130
Abstract: Cavity arrays have been identified as a potential passive device to disrupt and capture sweep events, which are responsible for the excess Reynolds stresses in the boundary layer. In the present study, the mechanism of the attenuation of captured sweep events has been analyzed, as well as the non-linear relationship between the volume of the backing cavity and the reduction in sweep intensity. The influence of cavity array on the turbulent boundary layer has been analyzed, with a total of six different backing cavity arrangements with varying volumes. Three of the backing cavities have been used to determine the non-linear relationship between the effectiveness of the cavity array in reducing sweep intensity and the volume of the backing cavity. The other three have been used to determine the mechanism by which the arrays manipulate the captured sweep events. The pre-multiplied energy spectra of multiple velocity histories were significantly reduced, by up to 12.5%, in the low and mid-range wavelength values (λx+& ), which is associated with the coherent structures. The results show that the maximum reduction in sweep intensity of approximately 7% may be obtained when Reθ = 3771. It has been demonstrated that the non-linear relationship between sweep event intensity reduction and cavity volume has reached an upper limit in this investigation. Results from this study have revealed that the cavity array weakens the sweep intensity of the captured sweep events by d ing the energy of the events through the friction losses in the cavity array and also in the large volume of the backing cavity.
Transient dynamics of accelerating turbulent pipe flow
Publisher: Cambridge University Press (CUP)
Date: 29-04-2021
DOI: 10.1017/JFM.2021.303
Effects of varied roughness coverage area on drag in a turbulent boundary layer using numerical simulations
Publisher: Elsevier BV
Date: 11-2023
The dominant mechanisms for each regime of secondary flows in horizontal particle-laden pipe flows
Publisher: Cambridge University Press (CUP)
Date: 23-09-2022
DOI: 10.1017/JFM.2022.745
Abstract: Numerical simulations have been conducted to identify the dominant mechanism responsible for driving secondary flow motions in horizontal particle-laden pipe flows, based on an analysis of the forces acting on each phase. A four-way coupling Euler–Lagrangian approach was employed, using direct numerical simulations for the gas phase and Lagrangian particle tracking to account for the drag, gravitational and lift forces, together with the interactions that occur for both particle–wall and inter-particle collisions. The four different flow regimes, which had been identified previously as depending on various combinations of flow parameters and are characterised by the secondary flow structures of both the fluid and particle phases, were identified via varying the mass loading alone from $\\varPhi _m=0.4$ to $\\varPhi _m=1.8$ . The distribution of the ergence of Reynolds stresses was used to help characterise the classes of the secondary fluid flow. This shows that secondary fluid flows of both the first and second kinds can either exist separately or co-exist in such flows. The forces exerted on the fluid phase by the pressure gradient and fluid–particle interactions were examined qualitatively and quantitatively to identify their contribution to the secondary fluid flow motions. A similar study was also applied to the drag, lift and gravitational forces exerted on the particle phase for the secondary particle flow motions. These were found to explain the secondary flows of both the fluid and particle phases with regard to both the flow direction and magnitude, together with the interaction between the two phases.
Flow regimes within horizontal particle-laden pipe flows
Publisher: Elsevier BV
Date: 10-2021
Characterisation of hydrogen jet flames under different pressures with varying coflow oxygen concentrations
Publisher: Elsevier BV
Date: 06-2023
The influence of pipe length on thermal statistics computed from DNS of turbulent heat transfer
Publisher: Elsevier BV
Date: 12-2011
Pulpal status of human primary molars with coexisting caries and physiological root resorption
Publisher: Wiley
Date: 17-10-2013
DOI: 10.1111/IPD.12070
Abstract: This study sought to investigate the effect of caries, in association with physiological root resorption, on the pulpal status of human primary molars. Fifty-three mandibular primary molars were obtained from children requiring extractions under general anaesthesia. Following extraction, teeth were split longitudinally and placed in Zamboni's fixative. Teeth were categorised according to i) the depth of caries (less than or greater than halfway through dentine thickness) and ii) the degree of physiological root resorption ( 67% of the root length). Ten-micrometre pulp sections were subject to indirect immunofluorescence using a combination of PGP 9.5 (a general neuronal marker), CD45 (a general neuronal marker), and Ulex europaeus agglutinin I (a marker of vascular endothelium). Image analysis was used to determine the percentage area of staining (PAS) for innervation and immune cells. Marked differences were seen between different s les, but there were no significant differences in mean PAS for PGP 9.5 or CD45 according to the degree of caries or extent of physiological root resorption (two-way anova, P > 0.05). Findings suggest that even if primary molars are undergoing exfoliation, they show comparable caries-induced changes to teeth without physiological root resorption, thus retaining potential for healing and repair.
Reynolds number dependence of large-scale friction control in turbulent channel flow
Publisher: American Physical Society (APS)
Date: 27-12-2016
Investigation of the influence of miniature vortex generators on the large-scale motions of a turbulent boundary layer
Publisher: Cambridge University Press (CUP)
Date: 07-12-2021
Abstract: Well resolved large-eddy simulation data are used to study the physical modulation effects of miniature vortex generators (MVGs) in a moderate Reynolds number zero pressure gradient turbulent boundary layer. Large-scale counter-rotating primary vortex pairs (PVPs) imposed by the MVG contribute to the formation of streamwise streaks by transporting high momentum fluids from the outer regions of the boundary layer towards the wall, giving rise to high-speed regions centred at the PVP. Consequently, low-speed regions are formed along the outer flank of the PVP, resulting in a pronounced alternating high- and low-speed flow pattern. The PVP also relates to regions with skin friction modification, where a local skin friction reduction of up to 15 % is obtained at the low-speed region, but the opposite situation is observed over the high-speed region. The MVG-induced flow feature is further investigated by spectral analysis of the triple decomposition velocity fluctuation. Pre-multiplied energy spectra of the streamwise MVG-induced velocity fluctuation reveal that the large-scale induced modes scale with the spanwise wavelength and the length of the MVG, but the energy peak is eventually repositioned to the size of the near-wall streaks in the streamwise direction. Analysis of the triple decomposition of the kinetic energy transport equations revealed the significance of the mean flow gradient in generating kinetic energy which sustains the secondary motion. There is also an energy transfer between the turbulent and MVG-induced kinetic energy independent of the mean flow.
Decomposition of the Reynolds shear stress in a turbulent boundary layer modified by miniature vortex generators
Publisher: American Physical Society (APS)
Date: 16-05-2022
Metronomic 5-Fluorouracil Delivery Primes Skeletal Muscle for Myopathy but Does Not Cause Cachexia
Publisher: MDPI AG
Date: 17-05-2021
DOI: 10.3390/PH14050478
Abstract: Skeletal myopathy encompasses both atrophy and dysfunction and is a prominent event in cancer and chemotherapy-induced cachexia. Here, we investigate the effects of a chemotherapeutic agent, 5-fluorouracil (5FU), on skeletal muscle mass and function, and whether small-molecule therapeutic candidate, BGP-15, could be protective against the chemotoxic challenge exerted by 5FU. Additionally, we explore the molecular signature of 5FU treatment. Male Balb/c mice received metronomic tri-weekly intraperitoneal delivery of 5FU (23 mg/kg), with and without BGP-15 (15 mg/kg), 6 times in total over a 15 day treatment period. We demonstrated that neither 5FU, nor 5FU combined with BGP-15, affected body composition indices, skeletal muscle mass or function. Adjuvant BGP-15 treatment did, however, prevent the 5FU-induced phosphorylation of p38 MAPK and p65 NF-B subunit, signalling pathways involved in cell stress and inflammatory signalling, respectively. This as associated with mitoprotection. 5FU reduced the expression of the key cytoskeletal proteins, desmin and dystrophin, which was not prevented by BGP-15. Combined, these data show that metronomic delivery of 5FU does not elicit physiological consequences to skeletal muscle mass and function but is implicit in priming skeletal muscle with a molecular signature for myopathy. BGP-15 has modest protective efficacy against the molecular changes induced by 5FU.
Transitional turbulent flow in a stenosed coronary artery with a physiological pulsatile flow
Publisher: Wiley
Date: 28-05-2020
DOI: 10.1002/CNM.3347
A Theoretical Review of Rotating Detonation Engines
Publisher: IntechOpen
Date: 14-01-2019
Abstract: Rotating detonation engines are a novel device for generating thrust from combustion, in a highly efficient, yet mechanically simple form. This chapter presents a detailed literature review of rotating detonation engines. Particular focus is placed on the theoretical aspects and the fundamental operating principles of these engines. The review covers both experimental and computational studies, in order to identify gaps in current understanding. This will allow the identification of future work that is required to further develop rotating detonation engines.
Advances in three-dimensional coronary imaging and computational fluid dynamics
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 08-2015
Dynamics of semi- and neutrally-buoyant particles in thermally stratified turbulent channel flow
Publisher: Elsevier BV
Date: 06-2021
Numerical study of geometric morphing wings of the 1303 UCAV
Publisher: Cambridge University Press (CUP)
Date: 22-03-2021
DOI: 10.1017/AER.2021.15
Abstract: Unmanned Combat Aerial Vehicles (UCAVs) are believed by many to be the future of aerial strike/reconnaissance capability. This belief led to the design of the UCAV 1303 by Boeing Phantom Works and the US Airforce Lab in the late 1990s. Because UCAV 1303 is expected to take on a wide range of mission roles that are risky for human pilots, it needs to be highly adaptable. Geometric morphing can provide such adaptability and allow the UCAV 1303 to optimise its physical feature mid-flight to increase the lift-to-drag ratio, manoeuvrability, cruise distance, flight control, etc. This capability is extremely beneficial since it will enable the UCAV to reconcile conflicting mission requirements (e.g. loiter and dash within the same mission). In this study, we conduct several modifications to the wing geometry of UCAV 1303 via Computational Fluid Dynamics (CFD) to analyse its aerodynamic characteristics produced by a range of different wing geometric morphs. Here we look into two specific geometric morphing wings: linear twists on one of the wings and linear twists at both wings (wash-in and washout). A baseline CFD of the UCAV 1303 without any wing morphing is validated against published wind tunnel data, before proceeding to simulate morphing wing configurations. The results show that geometric morphing wing influences the UCAV-1303 aerodynamic characteristics significantly, improving the coefficient of lift and drag, pitching moment and rolling moment.
An experimental model for pressure drop evaluation in a stenosed coronary artery
Publisher: AIP Publishing
Date: 02-2020
DOI: 10.1063/1.5139701
Abstract: Non-invasive measurement of pressure drop has great clinical significance for the treatment of coronary artery diseases. The objective of this study is to develop a relationship that can estimate pressure drop in a stenosed coronary artery model as a function of different parameters such as blood viscosity, artery length and diameter, flow rate and flow profile, and shape and degrees of stenosis. Experimental pressure measurements from a wide range of degrees of stenosis and critical simplified geometries of stenosis along with different unsteady flow profiles are employed to evaluate the pressure drop equation. To calculate the blockage term of the pressure drop, several experimental cases are investigated, and the results show that the blockage factor is strongly dependent on the shape and degree of stenosis. Furthermore, different unsteady flow profiles are applied to calculate the pulsatile pressure drop term, and it is found that the pulsatility parameter is not a function of the flow profile or the shape of the stenosis. However, it is only a function of the degree of stenosis. To test the validity of the developed equation, pressure drops through stenosed coronary artery models with the real physiological flow profile of the left and right coronary arteries were predicted and compared with the experimental measurements. The proposed equation is able to determine the pressure drop inside a stenosed coronary artery non-invasively using the measurement of the flow profile inside the artery as well as the images of the stenosed coronary artery obtained based on the non-invasive methods.
An investigation of channel flow with a smooth air–water interface
Publisher: Springer Science and Business Media LLC
Date: 06-2015
Drag Penalty Causing from the Roughness of Recently Cleaned and Painted Ship Hull Using RANS CFD
Publisher: Akademia Baru Publishing
Date: 25-03-2020
A Review on the Effect of Temporal Geometric Variations of the Coronary Arteries on the Wall Shear Stress and Pressure Drop
Publisher: ASME International
Date: 09-2021
DOI: 10.1115/1.4051923
Abstract: Temporal variations of the coronary arteries during a cardiac cycle are defined as the superposition of the changes in the position, curvature, and torsion of the coronary artery axis markers and the variations in the lumen cross-sectional shape due to the distensible wall motion induced by the pulse pressure and contraction of the myocardium in a cardiac cycle. This review discusses whether modeling of the temporal variations of the coronary arteries is needed for the investigation of hemodynamics specifically in time-critical applications such as a clinical environment. The numerical modelings in the literature that model or disregard the temporal variations of the coronary arteries on the hemodynamic parameters are discussed. The results in the literature show that neglecting the effects of temporal geometric variations is expected to result in about 5% deviation of the time-averaged pressure drop and wall shear stress values and also about 20% deviation of the temporal variations of hemodynamic parameters, such as time-dependent wall shear stress and oscillatory shear index. This review study can be considered as a guide for future studies to outline the conditions in which temporal variations of the coronary arteries can be neglected while providing a reliable estimation of hemodynamic parameters.
Simulation of a Large-Eddy-Break-up Device (LEBU) in a Moderate Reynolds Number Turbulent Boundary Layer
Publisher: Springer Science and Business Media LLC
Date: 11-08-2016
Swirling turbulent pipe flows: Inertial region and velocity–vorticity correlations
Publisher: Elsevier BV
Date: 02-2021
A new equivalent sand grain roughness relation for two-dimensional rough wall turbulent boundary layers
Publisher: Cambridge University Press (CUP)
Date: 08-04-2022
DOI: 10.1017/JFM.2022.242
Abstract: The effects of different geometries of two-dimensional (2-D) roughness elements in a zero pressure gradient (ZPG) turbulent boundary layer (TBL) on turbulence statistics and drag coefficient are assessed using single hot-wire anemometry. Three kinds of 2-D roughness are used: (i) circular rods with two different heights, $k= 1.6$ and 2.4 mm, and five different streamwise spacing of $s_{x}= 6k$ to $24k$ , (ii) three-dimensional (3-D) printed triangular ribs with heights of $k= 1.6$ mm and spacing of $s_{x}= 8k$ and (iii) computerized numerical control (CNC) machined sinewave surfaces with two different heights, $k= 1.6$ and 2.4 mm, and spacing of $s_{x}= 8k$ . These roughnesses cover a wide range of ratios of the boundary layer thickness to the roughness height ( $23 \\delta /k 41$ ), where $\\delta$ is the boundary layer thickness. All roughnesses cause a downward shift on the wall-unit normalised streamwise mean velocity profile when compared with the smooth wall profiles agreeing with the literature, with a maximum downward shift observed for $s_{x}= 8k$ . In the fully rough regime, the drag coefficient becomes independent of the Reynolds number. Changing the roughness height while maintaining the same spacing ratio $s_{x}/k$ exhibits little influence on the drag coefficient in the fully rough regime. On the other hand, the effective slope $(ES)$ and the height skewness $(k_{sk})$ appear to be major surface roughness parameters that affect the drag coefficient. These parameters are used in a new expression for $k_{s}$ , the equivalent sand grain roughness, developed for 2-D uniformly distributed roughness in the fully rough regime.
The influence of the coefficient of restitution on flow regimes within horizontal particle-laden pipe flows
Publisher: AIP Publishing
Date: 12-2021
DOI: 10.1063/5.0075440
Abstract: Numerical simulations of the particle-laden gas–solid flow in horizontal circular pipes have been used to identify the role of particle collision coefficients in flow regimes within it. A four-way coupling Euler–Lagrangian approach was employed, using direct numerical simulations of the gas phase and Lagrangian particle tracking to account for the drag, gravitational and lift forces, together with particle–wall and inter-particle interactions. The influences on the flow of the mass loading ratio (Φm) and of the coefficients of restitution for collisions both between particles and the wall (ep−w) and between particles (ep−p) are assessed by examining the fluid and particle velocities, particle concentration distribution, turbulence kinetic energy, static pressure, inter-phase transferred momentum, and the secondary flow motions of both the fluid and particle phases. Three dominant flow regimes that include three sub-regimes based on their secondary flow patterns are identified, the transition between which depends on the combination of Φm, ep−w, and ep−p. Additionally, the quantitative dependence of these transitions on these three parameters is also reported for a series of Stokes and Froude numbers.
Understanding of turbulence modulation and particle response in a particle-laden jet from direct numerical simulations
Publisher: Cambridge University Press (CUP)
Date: 13-10-2022
DOI: 10.1017/JFM.2022.764
Abstract: Point-particle direct numerical simulations have been employed to quantify the turbulence modulation and particle responses in a turbulent particle-laden jet in the two-way coupled regime with an inlet Reynolds number based on bulk velocity and jet diameter $({D_j})$ of ~10 000. The investigation focuses on three cases with inlet bulk Stokes numbers of 0.3, 1.4 and 11.2. Special care is taken to account for the particle–gas slip velocity and non-uniform particle concentrations at the nozzle outlet, enabling a reasonable prediction of particle velocity and concentration fields. Turbulence modulation is quantified by the variation of the gas-phase turbulent kinetic energy (TKE). The presence of the particle phase is found to d the gas-phase TKE in the near-field region within $5{D_j}$ from the inlet but subsequently increases the TKE in the intermediate region of (5–20) D j . An analysis of the gas-phase TKE transport equation reveals that the direct impact of the particle phase is to dissipate TKE via the particle-induced source term. However, the finite inertia of the particle phase affects the gas-phase velocity gradients, which indirectly affects the TKE production and dissipation, leading to the observed TKE attenuation and enhancement. Particle response to the gas-phase flow is quantified. Particles are found to exhibit notably stronger response to the gas-phase axial velocity than to the radial velocity. A new dimensionless figure is presented that collapses both the axial and radial components of the particle response as a function of the local Stokes number based on their respective integral length scales.
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
Backflow events under the effect of secondary flow of Prandtl's first kind
Publisher: American Physical Society (APS)
Date: 30-07-2020
Effect of shape of the stenosis on the hemodynamics of a stenosed coronary artery
Publisher: AIP Publishing
Date: 08-2021
DOI: 10.1063/5.0058765
Abstract: In this study, the effect of the shape of the stenosis on the flow transition in an artery is investigated. Different shapes of the stenosis including round, oval, elongated, half-moon, bean-shape, and crescent with and without eccentricity at a constant degree of stenosis (73%) are studied. A computational model, validated against the in-house Particle Image Velocimetry experimental results, is used to investigate the flow behavior. The results showed that the length of the jet region after the stenotic section varies significantly for different shapes of the stenosis. Based on the analysis of turbulent kinetic energy, power spectral density, and the spectral entropy of stream-wise velocity fluctuations, it was shown that eddies are formed after the dissipation of jet flow downstream of the stenosis. It was also shown that the intensity of the velocity fluctuations differs for different shapes of the stenosis. Furthermore, using the proper orthogonal decomposition method, it was shown that the shape of the stenosis has a significant impact on the downstream coherent structures. It was found that regardless of the degree of stenosis, specific shapes of the stenosis, such as round concentric, create less serious hemodynamic complications compared to the other shapes of the stenosis.
Associations of health-related quality of life with major adverse cardiovascular and cerebrovascular events for individuals with ischaemic heart disease: systematic review, meta-analysis and evidence
Publisher: BMJ
Date: 10-2023
A novel technique towards investigating wall shear stress within the stent struts using particle image velocimetry
Publisher: Springer Science and Business Media LLC
Date: 06-2021
Related Organisations
University Of Leeds
Location: United Kingdom of Great Britain and Northern Ireland
University Of Leeds School Of Medicine
Location: United Kingdom of Great Britain and Northern Ireland
University Of Reading
Location: United Kingdom of Great Britain and Northern Ireland
Related Funding Activities
Linkage Projects - Grant ID: LP160101753
Start Date: 12-2017
End Date: 12-2023
Amount: $440,000.00
Funder: Australian Research Council
View Funded ActivityDiscovery Early Career Researcher Award - Grant ID: DE180100157
Start Date: 06-2018
End Date: 06-2024
Amount: $366,446.00
Funder: Australian Research Council
View Funded Activity