ORCID Profile
0000-0003-0836-1524
Current Organisation
Monash University
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
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)
Fluidisation and Fluid Mechanics | Interdisciplinary Engineering | Computational Fluid Dynamics | Computational Heat Transfer | Biomedical Instrumentation | Nanotechnology | Medical Devices | Medical Physiology Not Elsewhere Classified | Biomedical Engineering | Mechanical Engineering | Heat And Mass Transfer Operations | Mechanical Engineering | Fluid Physics
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in Engineering | Effects of Climate Change and Variability on Australia (excl. Social Impacts) | Respiratory System and Diseases (incl. Asthma) | Public health not elsewhere classified | Urogenital system and disorders | Health related to ageing | Expanding Knowledge in the Biological Sciences | Treatments (e.g. chemicals, antibiotics) | Industrial machinery and equipment | Machined products |
Related Links
Publications
Measurement of instantaneous velocity and surface topography in the wake of a cylinder at low Reynolds number
Publisher: Elsevier BV
Date: 11-2008
Swirl mixing at microfluidic junctions due to low frequency side channel fluidic perturbations
Publisher: Elsevier BV
Date: 10-2010
From three-dimensional to quasi-two-dimensional: transient growth in magnetohydrodynamic duct flows
Publisher: Cambridge University Press (CUP)
Date: 19-12-2018
DOI: 10.1017/JFM.2018.863
Abstract: This study seeks to elucidate the linear transient growth mechanisms in a uniform duct with square cross-section applicable to flows of electrically conducting fluids under the influence of an external magnetic field. A particular focus is given to the question of whether at high magnetic fields purely two-dimensional mechanisms exist, and whether these can be described by a computationally inexpensive quasi-two-dimensional model. Two Reynolds numbers of $5000$ and $15\\,000$ and an extensive range of Hartmann numbers $0\\leqslant \\mathit{Ha}\\leqslant 800$ were investigated. Three broad regimes are identified in which optimal mode topology and non-modal growth mechanisms are distinct. These regimes, corresponding to low, moderate and high magnetic field strengths, are found to be governed by the independent parameters Hartmann number, Reynolds number based on the Hartmann layer thickness $R_{H}$ and Reynolds number built upon the Shercliff layer thickness $R_{S}$ , respectively. Transition between regimes respectively occurs at $\\mathit{Ha}\\approx 2$ and no lower than $R_{H}\\approx 33.\\dot{3}$ . Notably for the high Hartmann number regime, quasi-two-dimensional magnetohydrodynamic models are shown to be excellent predictors of not only transient growth magnitudes, but also the fundamental growth mechanisms of linear disturbances. This paves the way for a precise analysis of transition to quasi-two-dimensional turbulence at much higher Hartmann numbers than is currently achievable.
Application of a novel diffraction-based tomography method for imaging biological samples
Publisher: SPIE
Date: 17-10-2012
DOI: 10.1117/12.929444
Changing profile of couples seeking genetic counseling for consanguinity in Australia
Publisher: Wiley
Date: 22-11-2005
DOI: 10.1002/AJMG.A.30432
Abstract: Consanguineous marriage is rare in most Western countries and, for ex le, in the USA it may be subject to regulation by both civil legislation and religious prescription. This is not the case in many regions of Asia and Africa where marriage within the family is strongly favored. Since the 1970s there has been widespread migration to North America, Western Europe, and Australasia from communities which encourage consanguineous marriage. To assess the effect of this trend on a genetic counseling program, the records of 302 couples referred to Genetic Services of Western Australia for consanguinity counseling were abstracted for the period 1975-2001. Overall, a family history of genetic disease or a previously affected child was reported in 28.8% of cases. Premarital or prepregnancy counseling on grounds of consanguinity was sought by 41.0% of couples, and a further 18.2% of consanguineous couples had been referred because of a consanguineous pregnancy. In 7.6% of cases a relationship closer than first cousin was involved. Through time there was a significant increase in the numbers of consanguineous consultants, and their patterns of religious affiliation and ethnic origin widened markedly. Although effectively excluded from entry to Australia prior to 1975, couples of Asian origin accounted for 25.5% of all consanguineous consultants. With ongoing migration, changes in the ethnic profiles and the specific counseling requirements of consanguineous couples can be expected to continue and probably accelerate.
Effect of enclosure height on the structure and stability of shear layers induced by differential rotation
Publisher: Cambridge University Press (CUP)
Date: 15-01-2015
DOI: 10.1017/JFM.2014.727
Abstract: The structure and stability of Stewartson shear layers with different heights are investigated numerically via axisymmetric simulation and linear stability analysis, and a validation of the quasi-two-dimensional model is performed. The shear layers are generated in a rotating cylindrical tank with circular disks located at the lid and base imposing a differential rotation. The axisymmetric model captures both the thick and thin nested Stewartson layers, which are scaled by the Ekman number ( $\mathit{E}\,$ ) as $\mathit{E}\,^{1/4}$ and $\mathit{E}\,^{1/3}$ respectively. In contrast, the quasi-two-dimensional model only captures the $\mathit{E}\,^{1/4}$ layer as the axial velocity required to invoke the $\mathit{E}\,^{1/3}$ layer is excluded. A direct comparison between the axisymmetric base flows and their linear stability in these two models is examined here for the first time. The base flows of the two models exhibit similar flow features at low Rossby numbers ( $\mathit{Ro}$ ), with differences evident at larger $\mathit{Ro}$ where depth-dependent features are revealed by the axisymmetric model. Despite this, the quasi-two-dimensional model demonstrates excellent agreement with the axisymmetric model in terms of the shear-layer thickness and predicted stability. A study of various aspect ratios reveals that a Reynolds number based on the theoretical Ekman layer thickness is able to describe the transition of a base flow that is reflectively symmetric about the mid-plane to a symmetry-broken state. Additionally, the shear-layer thicknesses scale closely to the expected ${\it\delta}_{vel}\propto A\mathit{E}\,^{1/4}$ and ${\it\delta}_{vort}\propto A\mathit{E}\,^{1/3}$ for shear layers that are not affected by the confinement ( $A\mathit{E}\,^{1/4}\lesssim 0.34$ in this system, the ratio of tank height to shear-layer radius). The linear stability analysis reveals that the ratio of Stewartson layer radius to thickness should be greater than $45$ for the stability of the flow to be independent of aspect ratio. Thus, for sufficiently small $A\mathit{E}\,^{1/4}$ and $A\mathit{E}\,^{1/3}$ , the flow characteristics remain similar and the linear stability of the flow can be described universally when the azimuthal wavelength is scaled against $A$ . The analysis also recovers an asymptotic scaling for the normalized azimuthal wavelength which suggests that ${\it\lambda}_{{\it\theta},c}^{\ast }\propto (|\mathit{Ro}|/\mathit{E}\,^{2})^{-1/5}$ for geometry-independent shear layers at marginal stability.
Effect of hemodynamic forces on platelet aggregation geometry
Publisher: Springer Science and Business Media LLC
Date: 04-01-2011
DOI: 10.1007/S10439-010-0239-4
Abstract: The shear rate dependence of platelet aggregation geometries is investigated using a combination of in vitro and numerical experiments. Changes in upstream shear rate, γ(Pw), are found to cause systematic changes in mature platelet aggregation geometries. However, γ(Pw) is not the only factor determining the shear rate experienced by a platelet moving over, and adhering to, a platelet aggregation: flow simulations demonstrate that naturally occurring variations in platelet aggregation geometry cause the local shear rate on the surface of a mature platelet aggregation to vary between zero and up to eight times γ(Pw). Additionally, as a platelet aggregation grows, systematic changes in geometry are found, indicating that the local shear field over a growing platelet aggregation will differ from that over mature platelet aggregations.
Spatial evolution of a quasi-two-dimensional Kármán vortex street subjected to a strong uniform magnetic field
Publisher: AIP Publishing
Date: 05-2015
DOI: 10.1063/1.4919906
Abstract: A vortex decay model for predicting spatial evolution of peak vorticity in a wake behind a cylinder is presented. For wake vortices in the stable region behind the formation region, results have shown that the presented model has a good capability of predicting spatial evolution of peak vorticity within an advecting vortex across 0.1 ≤ β ≤ 0.4, 500 ≤ H ≤ 5000, and 1500 ≤ ReL ≤ 8250. The model is also generalized to predict the decay behaviour of wake vortices in a class of quasi-two-dimensional magnetohydrodynamic duct flows. Comparison with published data demonstrates remarkable consistency.
Subharmonic mechanism of the mode C instability
Publisher: AIP Publishing
Date: 11-2005
DOI: 10.1063/1.2139682
Abstract: The perturbation field of the recently discovered subharmonic mode C instability in the wake behind a ring is compared via a side-by-side comparison to the perturbation fields of the modes A and B instabilities familiar from past studies of the vortex street behind a circular cylinder. Snapshots of the wake are presented over a full shedding cycle, along with evidence from a linear stability analysis, to verify and better understand how the subharmonic instability is sustained.
On quasiperiodic and subharmonic Floquet wake instabilities
Publisher: AIP Publishing
Date: 03-2010
DOI: 10.1063/1.3368106
Abstract: The physical characteristics of bifurcated states in systems with inherent symmetry are constrained in ways that those in systems with broken symmetry are not. Here we examine the issue of quasiperiodic versus subharmonic instability modes of time-periodic laminar wakes, and how the relationship between them is influenced by weak symmetry breaking. The ex les used are the vortex street wake of a circular cylinder, where symmetry is broken by distorting the cylinder into a ring, and the wake of a square cylinder, where symmetry is broken by a small fixed rotation of the cylinder about its axis. In both cases the symmetric wakes exhibit a quasiperiodic instability mode, with a pair of complex-conjugate Floquet multipliers and which manifests as a traveling wave. As symmetry is broken these multipliers migrate continuously to the real axis, coalesce, and split into a pair of subharmonic multipliers that move apart along the negative real axis. This behavior resolves an apparent dichotomy between the previously established theoretical results and numerical predictions for the symmetric wake systems, and the predictions and experimental observations for systems with weakly broken symmetry.
Wake transition of two-dimensional cylinders and axisymmetric bluff bodies
Publisher: Elsevier BV
Date: 08-2006
Horizontal convection: Effect of aspect ratio on Rayleigh number scaling and stability
Publisher: Elsevier BV
Date: 04-2011
From spheres to circular cylinders: non-axisymmetric transitions in the flow past rings
Publisher: Cambridge University Press (CUP)
Date: 10-05-2004
Flow dynamics and wall shear-stress variation in a fusiform aneurysm
Publisher: Springer Science and Business Media LLC
Date: 04-12-2008
Surface topography of jet shock cells in a hydraulic analogy
Publisher: Springer Science and Business Media LLC
Date: 04-04-2010
Preface to special issue: Part I of selected papers from CFD in the minerals and process industries
Publisher: SAGE Publications
Date: 09-2010
Application of Particle Image Velocimetry and Reference Image Topography to jet shock cells using the hydraulic analogy
Publisher: Springer Science and Business Media LLC
Date: 24-03-2011
Combining an obstacle and electrically driven vortices to enhance heat transfer in a quasi-two-dimensional MHD duct flow
Publisher: Cambridge University Press (CUP)
Date: 03-03-2016
DOI: 10.1017/JFM.2016.90
Abstract: The design of vortex promoters in a heated-wall duct is often limited by the considerations of practicality, especially in complex systems such as fusion blankets. The present study investigates the use of current injection to invoke a street of vortices in quasi-two-dimensional high transverse magnetic field magnetohydrodynamic duct flows to enhance instability behind a cylinder. The intent is to generate intensive flow vorticity parallel to a magnetic field downstream of a field-aligned cylinder. Electric current enters the flow through an electrode embedded in one of the Hartmann walls, radiates outward, imparting a rotational forcing around the electrode due to the Lorentz force. The quasi-two-dimensional nature of these flows then promotes a vortical rotation across the interior of the duct with axis aligned to the magnetic field. The hot and cold walls are parallel to the magnetic field. Electric current litude and pulse width, excitation frequency and electrode position are systematically varied to explore their influences on the convective heat transport phenomenon. This investigation builds on a recommendation from previous work of Bühler ( J. Fluid Mech. , vol. 326, 1996, pp. 125–150) dedicated to understanding of the flow stability in a similar configuration. This study provides supportive evidence for the use of current injection as an alternative to the conventional mechanically actuated turbuliser, with heat transfer almost doubled for negligible additional pumping power requirements.
Cylinders with square cross-section: Wake instabilities with incidence angle variation
Publisher: Cambridge University Press (CUP)
Date: 10-07-2009
DOI: 10.1017/S0022112009006879
Abstract: The wakes behind square cylinders with variation in incidence angle are computed over a range of Reynolds numbers to elucidate the three-dimensional stability and dynamics up to a Reynolds number of Re = 300, based on the projected height of the inclined square cylinder. Three-dimensional instability modes are predicted and computed using a linear stability analysis technique and three-dimensional simulations, respectively. Depending on the incidence angle, the flow is found to transition to three-dimensional flow through either a mode A instability, or a subharmonic mode C instability. The mode A instability is predicted as the first-occurring instability at incidence angles smaller than 12° and greater than 26°, with the mode C instability predicted between these incidence angles. At a zero-degree angle of incidence, the wake instabilities closely match modes A, B and a quasi-periodic mode predicted in earlier studies behind square and circular cylinders. With increasing angle of incidence, the three-dimensional wake transition Reynolds number first increases from Re = 164 as the mode A instability weakens, before decreasing again beyond an incidence angle of 12° as the wake becomes increasingly unstable to the mode C instability, and then again to the mode A instability as the incidence angle approaches 45°. A spanwise autocorrelation analysis from computations over a cylinder span 20 times the square cross-section side length reveals that beyond the onset of three-dimensional instabilities, the vortex street breaks down with patterns consistent with spatio-temporal chaos. This effect was more pronounced at higher incidence angles.
Flow around an impulsively arrested circular cylinder
Publisher: AIP Publishing
Date: 08-2007
DOI: 10.1063/1.2754346
Abstract: The vortex dynamics of the flow around a suddenly arrested translating circular cylinder is investigated by direct numerical simulation and water tank experiments. In the numerical study, a method of visualization of streaklines in simulated-particle tracking computations is proposed, which is based on a variable-variance two-dimensional Gaussian-weighted summation of particles in the vicinity of each interpolation point, and for which a close similarity with physical dye visualizations is found. This technique is used to identify the trajectory of both the wake vortices, as well as the secondary vortices induced as the original wake convects over the arrested cylinder. Observations show that, in a fashion similar to the flow past an arresting sphere, each wake vortex induces a counter-rotating vortex pair, which subsequently self-propels over a range of sometimes surprising trajectories as the Reynolds number and cylinder translation distance are varied. At low Reynolds numbers and short translation distances, the wake vortices propel past the cylinder, continuing in the direction of the original cylinder motion. At higher Reynolds numbers, the vortices deviate outwards in circular arcs of increasing curvature, even to the extent that the vortex pairs collide behind the cylinder. These trajectory curvatures are analyzed with respect to the circulation of the vortex pairs. At sufficiently long translation distances, a wake instability destroys the reflective symmetry about the wake centerline. This regime is investigated by both comparison with experiment and analysis of the discrepancy between the vorticity and particle fields at large post-arrest times.
Heat transfer enhancement using rectangular vortex promoters in confined quasi-two-dimensional magnetohydrodynamic flows
Publisher: Elsevier BV
Date: 02-2016
Erythrocyte deformation in a microfluidic cross-slot channel
Publisher: Royal Society of Chemistry (RSC)
Date: 20-08-2014
DOI: 10.1039/C4RA04229H
Haemodynamic forces on in vitro thrombi: A numerical analysis
Publisher: Springer Science and Business Media LLC
Date: 16-03-2012
DOI: 10.1007/S11517-012-0891-Y
Abstract: The flow of blood past an axisymmetric thrombus analogue, within an in vitro geometry, is computed via solution of the discrete three-dimensional (3D) Navier-Stokes equations. Particle tracking is used to model the behaviour of thrombocytes (platelets) moving throughout the domain and to investigate behaviour with respect to the platelets. The system is explored using shear rate to quantify the effects an idealised thrombus has with respect to an undisturbed in vitro geometry over 'Poiseuille flow' shear rate conditions applicable to in vivo and in vitro experiments (1,200-10,000 s⁻¹). Local shear rate variations show peaks in shear rate greater than double that of Poiseuille flow conditions. These local shear rate variations are observed to be non-linear, despite the low Reynolds number (5.2-43.4) within the system. Topological transitions of shear rate are observed, limiting the height of peak shear rate within the system, suggesting a thrombus growth limiting behaviour. Temporal gradients of shear rate, measured with respect to in idual platelets, were calculated. Multiple regions of peak shear rate gradient were observed throughout the flow, suggesting that platelet-platelet interaction may not be limited to regions near to the surface of the thrombus.
Optimal transient disturbances behind a circular cylinder in a quasi-two-dimensional magnetohydrodynamic duct flow
Publisher: AIP Publishing
Date: 02-2012
DOI: 10.1063/1.3686809
Abstract: The transient response of optimal linear perturbations of liquid metal flow under a strong axial magnetic field in an electrically insulated rectangular duct is considered. The focus is on the subcritical regime, below the onset of von Kármán vortex shedding, to determine the role of optimal disturbances in developing wake instabilities. In this configuration, the flow is quasi-two-dimensional and can be solved over a two-dimensional domain. Parameter ranges considered include Reynolds numbers \\documentclass[12pt]{minimal}\\begin{document}$50 \\le \\mbox{\\textit {Re}}\\lesssim 2100$\\end{document}50≤Re≲2100, modified Hartmann numbers \\documentclass[12pt]{minimal}\\begin{document}$50 \\le {\\mbox{\\textit {Ha}}^\\star }\\lesssim 500$\\end{document}50≤Ha★≲500, and blockage ratios 0.1 ⩽ β ⩽ 0.4. In some instances, the optimal disturbances are found to generate energy growth of greater than four orders of magnitude. Variation in the wake recirculation length in the steady flow regime is determined as a function of Reynolds number, Hartman number, and blockage ratio, and a universal expression is proposed. For all β, the energy lification of the disturbances is found to decrease significantly with increasing Hartmann number and the peak growth shifts towards smaller times. The optimal initial disturbances are consistently located in the vicinity of the boundary layer separation from the cylinder, and the structure of these disturbances is consistent for all Hartmann numbers and blockage ratios considered in this study. The time evolution of the optimal perturbations is presented, and is shown to correspond to sinuous oscillations of the shear layer downstream of the wake recirculation. The critical Reynolds number for the onset of growth at different Hartmann numbers and blockage ratios is determined. It is found that it increases rapidly with increasing Hartmann number and blockage ratio. For all β, the peak energy lification grows exponentially with \\documentclass[12pt]{minimal}\\begin{document}$\\mbox{\\textit {Re}}$\\end{document}Re at low and high Hartmann numbers. Direct numerical simulation in which the inflow is perturbed by a random white noise confirms the predictions arising from the transient growth analysis: that is, the perturbation excites and feeds energy into the global mode.
Subcritical transition to turbulence in quasi-two-dimensional shear flows
Publisher: Cambridge University Press (CUP)
Date: 19-05-2023
DOI: 10.1017/JFM.2023.345
Abstract: The transition to turbulence in conduits is among the longest-standing problems in fluid mechanics. Challenges in producing or saving energy hinge on understanding promotion or suppression of turbulence. While a global picture based on an intrinsically 3-D subcritical mechanism is emerging for 3-D turbulence, subcritical turbulence is yet to even be observed when flows approach two dimensions, e.g. under intense rotation or magnetic fields. Here, stability analysis and direct numerical simulations demonstrate a subcritical quasi-two-dimensional (quasi-2-D) transition from laminar flow to turbulence, via a radically different 2-D mechanism to the 3-D case, driven by nonlinear Tollmien–Schlichting waves. This alternative scenario calls for a new line of thought on the transition to turbulence and should inspire new strategies to control transition in rotating devices and nuclear fusion reactor blankets.
Flow normal to a short cylinder with hemispherical ends
Publisher: AIP Publishing
Date: 04-2008
DOI: 10.1063/1.2899782
Abstract: The flow normal to a cylinder with hemispherical ends is computed using a spectral-element/Fourier method. With variation in the ratio of cylinder length to diameter, this body varies smoothly from a sphere to a straight circular cylinder, providing insight into the relationship between body topology and wake dynamics. This letter displays the wake structure for a range of cylinder lengths up to a Reynolds number of 300 and considers the wake alignment and symmetry at length ratios approaching a spherical body. A time-invariant wake consistent with that behind a sphere is found to preferentially align with a symmetry plane bisecting the major axis of short cylinders, whereas the periodic “hairpin” wake aligns with the minor axis thus the hairpin vortices shed from alternate sides of the cylinder, just as with Kármán vortex shedding from a circular cylinder. The plane of symmetry is found to break via a supercritical transition at a Reynolds number of 350±2.
The evolution of a subharmonic mode in a vortex street
Publisher: Cambridge University Press (CUP)
Date: 21-06-2005
Dynamics and heat transfer in a quasi-two-dimensional MHD flow past a circular cylinder in a duct at high Hartmann number
Publisher: Elsevier BV
Date: 02-2011
Linear stability and energetics of rotating radial horizontal convection
Publisher: Cambridge University Press (CUP)
Date: 13-04-2016
DOI: 10.1017/JFM.2016.193
Abstract: The effect of rotation on horizontal convection in a cylindrical enclosure is investigated numerically. The thermal forcing is applied radially on the bottom boundary from the coincident axes of rotation and geometric symmetry of the enclosure. First, a spectral element method is used to obtain axisymmetric basic flow solutions to the time-dependent incompressible Navier–Stokes equations coupled via a Boussinesq approximation to a thermal transport equation for temperature. Solutions are obtained primarily at Rayleigh number $\\mathit{Ra}=10^{9}$ and rotation parameters up to $Q=60$ (where $Q$ is a non-dimensional ratio between thermal boundary layer thickness and Ekman layer depth) at a fixed Prandtl number $\\mathit{Pr}=6.14$ representative of water and enclosure height-to-radius ratio $H/R=0.4$ . The axisymmetric solutions are consistently steady state at these parameters, and transition from a regime unaffected by rotation to an intermediate regime occurs at $Q\\approx 1$ in which variation in thermal boundary layer thickness and Nusselt number are shown to be governed by a scaling proposed by Stern (1975, Ocean Circulation Physics . Academic). In this regime an increase in $Q$ sees the flow accumulate available potential energy and more strongly satisfy an inviscid change in potential energy criterion for baroclinic instability. At the strongest $Q$ the flow is dominated by rotation, accumulation of available potential energy ceases and horizontal convection is suppressed. A linear stability analysis reveals several instability mode branches, with dominant wavenumbers typically scaling with $Q$ . Analysis of contributing terms of an azimuthally averaged perturbation kinetic energy equation applied to instability eigenmodes reveals that energy production by shear in the axisymmetric mean flow is negligible relative to that produced by conversion of available potential energy from the mean flow. An evolution equation for the quantity that facilitates this exchange, the vertical advective buoyancy flux, reveals that a baroclinic instability mechanism dominates over $5\\lesssim Q\\lesssim 30$ , whereas stronger and weaker rotations are destabilised by vertical thermal gradients in the mean flow.
Linear stability of confined flow around a 180-degree sharp bend
Publisher: Cambridge University Press (CUP)
Date: 09-06-2017
DOI: 10.1017/JFM.2017.266
Abstract: This study seeks to characterise the breakdown of the steady two-dimensional solution in the flow around a 180-degree sharp bend to infinitesimal three-dimensional disturbances using a linear stability analysis. The stability analysis predicts that three-dimensional transition is via a synchronous instability of the steady flows. A highly accurate global linear stability analysis of the flow was conducted with Reynolds number $\\mathit{Re} $ and bend opening ratio (ratio of bend width to inlet height) $0.2\\leqslant \\unicode[STIX]{x1D6FD}\\leqslant 5$ . This range of $\\mathit{Re}$ and $\\unicode[STIX]{x1D6FD}$ captures both steady-state two-dimensional flow solutions and the inception of unsteady two-dimensional flow. For $0.2\\leqslant \\unicode[STIX]{x1D6FD}\\leqslant 1$ , the two-dimensional base flow transitions from steady to unsteady at higher Reynolds number as $\\unicode[STIX]{x1D6FD}$ increases. The stability analysis shows that at the onset of instability, the base flow becomes three-dimensionally unstable in two different modes, namely a spanwise oscillating mode for $\\unicode[STIX]{x1D6FD}=0.2$ and a spanwise synchronous mode for $\\unicode[STIX]{x1D6FD}\\geqslant 0.3$ . The critical Reynolds number and the spanwise wavelength of perturbations increase as $\\unicode[STIX]{x1D6FD}$ increases. For $1 \\unicode[STIX]{x1D6FD}\\leqslant 2$ both the critical Reynolds number for onset of unsteadiness and the spanwise wavelength decrease as $\\unicode[STIX]{x1D6FD}$ increases. Finally, for $2 \\unicode[STIX]{x1D6FD}\\leqslant 5$ , the critical Reynolds number and spanwise wavelength remain almost constant. The linear stability analysis also shows that the base flow becomes unstable to different three-dimensional modes depending on the opening ratio. The modes are found to be localised near the reattachment point of the first recirculation bubble.
Stability characteristics of a counter-rotating unequal-strength Batchelor vortex pair
Publisher: Cambridge University Press (CUP)
Date: 06-03-2012
DOI: 10.1017/JFM.2012.55
Abstract: A Batchelor vortex represents the asymptotic solution of a trailing vortex in an aircraft wake. In this study, an unequal-strength, counter-rotating Batchelor vortex pair is employed as a model of the wake emanating from one side of an aircraft wing this model is a direct extension of several prior investigations that have considered unequal-strength Lamb–Oseen vortices as representations of the aircraft wake problem. Both solution of the linearized Navier–Stokes equations and direct numerical simulations are employed to study the linear and nonlinear development of a vortex pair with a circulation ratio of $\\Lambda = \\ensuremath{-} 0. 5$ . In contrast to prior investigations considering a Lamb–Oseen vortex pair, we note strong growth of the Kelvin mode $[\\ensuremath{-} 2, 0] $ coupled with an almost equal growth rate of the Crow instability. Three stages of nonlinear instability development are defined. In the initial stage, the Kelvin mode litude becomes sufficiently large that oscillations within the core of the weaker vortex are easily observable and significantly affect the profile of the weaker vortex. In the secondary stage, filaments of secondary vorticity emanate from the weaker vortex and are convected around the stronger vortex. In the tertiary stage, a transition in the dominant instability wavelength is observed from the short-wavelength Kelvin mode to the longer-wavelength Crow instability. Much of the instability growth is observed on the weaker vortex of the pair, although small perturbations in the stronger vortex are observed in the tertiary nonlinear growth phase.
Transition to turbulence in quasi-two-dimensional MHD flow driven by lateral walls
Publisher: American Physical Society (APS)
Date: 14-01-2021
Transitions and scaling in horizontal convection driven by different temperature profiles
Publisher: Elsevier BV
Date: 02-2020
Pressure-driven flow past spheres moving in a circular tube
Publisher: Cambridge University Press (CUP)
Date: 14-11-2007
DOI: 10.1017/S0022112007008543
Abstract: A computational investigation, supported by a theoretical analysis, is performed to investigate a pressure-driven flow around a line of equispaced spheres moving at a prescribed velocity along the axis of a circular tube. This fundamental study underpins a range of applications including physiological circulation research. A spectral-element formulation in cylindrical coordinates is employed to solve for the incompressible fluid flow past the spheres, and the flows are computed in the reference frame of the translating spheres. Both the volume flow rate relative to the spheres and the forces acting on each sphere are computed for specific sphere-to-tube diameter ratios and sphere spacing ratios. Conditions at which zero axial force on the spheres are identified, and a region of unsteady flow is detected at higher Reynolds numbers (based on tube diameter and sphere velocity). A regular perturbation analysis and the reciprocal theorem are employed to predict flow rate and drag coefficient trends at low Reynolds numbers. Importantly, the zero drag condition is well-described by theory, and states that at this condition, the sphere velocity is proportional to the applied pressure gradient. This result was verified for a range of spacing and diameter ratios. Theoretical approximations agree with computational results for Reynolds numbers up to O (100). The geometry dependence of the zero axial force condition is examined, and for a particular choice of the applied dimensionless pressure gradient, it is found that this condition occurs at increasing Reynolds numbers with increasing diameter ratio, and decreasing Reynolds number with increasing sphere spacing. Three-dimensional simulations and predictions of a Floquet linear stability analysis independently elucidate the bifurcation scenario with increasing Reynolds number for a specific diameter ratio and sphere spacing. The steady axisymmetric flow first experiences a small region of time-dependent non-axisymmetric instability, before undergoing a regular bifurcation to a steady non-axisymmetric state with azimuthal symmetry m = 1. Landau modelling verifies that both the regular non-axisymmetric mode and the axisymmetric Hopf transition occur through a supercritical (non-hysteretic) bifurcation.
Heat transfer in a high Hartmann number MHD duct flow with a circular cylinder placed near the heated side-wall
Publisher: Elsevier BV
Date: 12-2013
Enhancing heat transfer in a high Hartmann number magnetohydrodynamic channel flow via torsional oscillation of a cylindrical obstacle
Publisher: AIP Publishing
Date: 11-2012
DOI: 10.1063/1.4767515
Abstract: An approach is studied for side-wall heat transfer enhancement in the magnetohydrodynamic flow of fluid in a rectangular duct that is d ed by a strong transverse magnetic field. The mechanism employs the rotational oscillation of a cylinder placed inside the duct to encourage vortex shedding, which promotes the mixing of fluid near a hot duct wall with cooler fluid in the interior. The effectiveness of the heat transfer enhancement is investigated over a wide range of oscillation litudes and forcing frequencies. The motivation for exploring this mechanism is inspired by the transient growth response of this flow, which indicates that the optimal disturbances feeding the vortex shedding process are localized near the cylinder, and are characterized by an asymmetrical disturbance with respect to the wake centreline. The results show that a considerable increase in heat transfer from the heated channel wall due to rotational oscillation of the cylinder can be achieved, with the maximum enhancement of more than 30% over a zone extending 10d downstream of the cylinder. As the angular velocity litude of oscillation is increased, the range of oscillation frequencies for effective enhancement is widened, and the frequency at which the peak Nusselt number occurs is shifted slightly to lower frequencies. As the litude is increased, the formation of strong discrete wake vortices draws fluid from the wall boundary layers into the wake, enhancing heat transfer. The effect of oscillation litude on the distribution of local Nusselt number \\documentclass[12pt]{minimal}\\begin{document}$\\textit {Nu}_w$\\end{document}Nuw along the heated wall is significant. With an increase in Reynolds number, scope for additional heat transfer enhancement is possible.
Non-axisymmetric flows in a differential-disk rotating system
Publisher: Cambridge University Press (CUP)
Date: 25-06-2015
DOI: 10.1017/JFM.2015.270
Abstract: The non-axisymmetric structure of an unstable Stewartson shear layer generated via a differential rotation between flush disks and a cylindrical enclosure is investigated numerically using both three-dimensional direct numerical simulation and a quasi-two-dimensional model. Previous literature has only considered the depth-independent quasi-two-dimensional model due to its low computational cost. The three-dimensional model implemented here highlights the supercritical instability responsible for the polygonal deformation of the shear layer in the linear and nonlinear growth regimes and reveals that linear stability analysis is capable of accurately determining the preferred azimuthal wavenumber for flow conditions near the onset of instability. This agreement is lost for sufficiently forced flows where nonlinear effects encourage the coalescence of vortices towards lower-wavenumber structures. Time-dependent flows are found for large Reynolds numbers defined based on the Stewartson layer thickness and azimuthal velocity differential. However, this temporal behaviour is not solely characterized by Reynolds number but is rather a function of both the Rossby and Ekman numbers. At high Ekman and Rossby numbers, unsteady flow emerges through a small-scale azimuthal destabilization of the axial jets within the Stewartson layers at low Ekman numbers, unsteady flow emerges through a modulation in the strength of one of the axial vortices rolled up by non-axisymmetric instability of the Stewartson layer.
Experimental study of simultaneous measurement of velocity and surface topography: In the wake of a circular cylinder at low Reynolds number
Publisher: Springer Science and Business Media LLC
Date: 22-08-2011
Cardiogenic Airflow in the Lung Revealed Using Synchrotron-Based Dynamic Lung Imaging
Publisher: Springer Science and Business Media LLC
Date: 21-03-2018
DOI: 10.1038/S41598-018-23193-W
Abstract: The beating heart is known to produce pressure and airflow oscillations in the lungs of mammals. This phenomenon is often disregarded as detailed measurement of its effects in the lung have hitherto not been possible. Previous studies have attempted to measure the effect of these oscillations on gas mixing. However, the results have proven inconclusive, due to the lack of a direct measurement tool capable of flow measurement throughout the entire bronchial tree. Here we present the first detailed measurement of cardiogenic oscillations, using synchrotron-based dynamic lung imaging of live mechanically ventilated mice. The results demonstrate large flow oscillations and pendelluft in the airways due to the mechanical action of the beating heart. Using a virtual tracer modelling analysis we show that cardiogenic oscillations produced up to 4 times increased gas mixing, but only in the absence of tidal ventilation. The results highlight the importance of considering this often-disregarded phenomenon when investigating lung function, particularly in situations where tidal ventilation is reduced or absent.
Subcritical route to turbulence via the Orr mechanism in a quasi-two-dimensional boundary layer
Publisher: American Physical Society (APS)
Date: 23-11-2020
Polynomial element velocimetry (PEV): a technique for continuous in-plane velocity and velocity gradient measurements for low Reynolds number flows
Publisher: IOP Publishing
Date: 14-08-2012
The origin of instability in enclosed horizontally driven convection
Publisher: Elsevier BV
Date: 03-2016
Symmetry breaking and instability mechanisms in medium depth torsionally driven open cylinder flows
Publisher: Cambridge University Press (CUP)
Date: 14-02-2011
DOI: 10.1017/S0022112010006129
Abstract: A numerical investigation was conducted into the different flow states, and bifurcations leading to changes of state, found in open cylinders of medium to moderate depth driven by a constant rotation of the vessel base. A combination of linear stability analysis, for cylinders of numerous height-to-radius aspect ratios ( H / R ), and nonlinear stability analysis and three-dimensional simulations for a cylinder of aspect ratio 1.5, has been employed. Attention is focused on the breaking of SO (2) symmetry. A comprehensive map of transition Reynolds numbers as a function of aspect ratio is presented by combining a detailed stability analysis with the limited existing data from the literature. For all aspect ratios considered, the primary instabilities are identified as symmetry-breaking Hopf bifurcations, occurring at Reynolds numbers well below those of the previously reported axisymmetric Hopf transitions. It is revealed that instability modes with azimuthal wavenumbers m = 1, 3 and 4 are the most unstable in the range 1.0 H / R 4, and that numerous double Hopf bifurcation points exist. Critical Reynolds numbers generally increase with cylinder aspect ratio, though a decrease in stability occurs between aspect ratios 1.5 and 2.0, where a local minimum in critical Reynolds number occurs. For H / R = 1.5, a detailed characterisation of instability modes is given. It is hypothesized that the primary instability leading to transition from steady axisymmetric flow to unsteady three-dimensional flow is related to deformation of shear layers that are present in the flow, in particular at the interfacial region between the vortex breakdown bubble and the primary recirculation.
Low Reynolds number instabilities and transitions in bluff body wakes
Publisher: IOP Publishing
Date: 04-2007
From spheres to circular cylinders: the stability and flow structures of bluff ring wakes
Publisher: Cambridge University Press (CUP)
Date: 10-10-2003
Linear stability analysis of a shear layer induced by differential coaxial rotation within a cylindrical enclosure
Publisher: Cambridge University Press (CUP)
Date: 05-12-2013
DOI: 10.1017/JFM.2013.594
Abstract: The generation of distinct polygonal configurations via the instability of a Stewartson shear layer is numerically investigated. The shear layer is induced using a rotating cylindrical tank with differentially forced disks located at the top and bottom boundaries. The incompressible Navier–Stokes equations are solved on a two-dimensional semi-meridional plane. Axisymmetric base flows are consistently found to reach a steady state for a wide range of flow conditions, and details of the vertical structure are revealed. An axially invariant two-dimensional flow is ascertained for small $\\vert \\mathit{Ro}\\vert $ , which substantiates the Taylor–Proudman theorem. Sufficient increases in $\\vert \\mathit{Ro}\\vert $ forcing develops flow features that break this quasi-two-dimensionality. The onset of this breaking occurs earlier with increasing $\\vert \\mathit{Ro}\\vert $ for $\\mathit{Ro}\\gt 0$ compared with $\\mathit{Ro}\\lt 0$ . The thickness scaling of the vertical Stewartson layers are in agreement with previous analytical results. Growth rates of the most unstable azimuthal wavenumber from a global linear stability analysis are obtained. The threshold between axisymmetric and non-axisymmetric flow follows a power law, and both positive- and negative- $\\mathit{Ro}$ regimes are found to adopt the same threshold for instability, namely $\\vert \\mathit{Ro}\\vert \\geq 18. 1{E}^{0. 767} $ . This relationship corresponds to a constant critical internal Reynolds number of ${\\mathit{Re}}_{i, c} \\simeq 22. 5$ . A review of reported critical internal Reynolds number and their characteristic length scales yields a consistent instability onset given by $\\vert \\mathit{Ro}\\vert / {E}^{3/ 4} = 15. 4{\\unicode{x2013}} 16. 6$ here we find $\\vert \\mathit{Ro}\\vert / {E}^{3/ 4} = 15. 8$ . At the onset of linear instability, the initially circular shear layer deforms, resulting in a polygonal structure consistent with barotropic instability. Dominant azimuthal wavenumbers range from $3$ to $7$ at the onset of instability for the parameter space explored. Empirical relationships for the preferential wavenumber have been obtained. Additional instability modes have been discovered that favour higher wavenumbers, and these exhibit structures localized to the disk–tank interfaces.
Horizontal convection in shallow enclosures scales with height, not length, at low Rayleigh numbers
Publisher: Elsevier BV
Date: 12-2019
Asymmetric structure and non-linear transition behaviour of the wakes of toroidal bodies
Publisher: Elsevier BV
Date: 2004
Linear stability of horizontal, laminar fully developed, quasi-two-dimensional liquid metal duct flow under a transverse magnetic field and heated from below
Publisher: American Physical Society (APS)
Date: 10-03-2017
High resolution optical calorimetry for synchrotron microbeam radiation therapy
Publisher: IOP Publishing
Date: 10-03-2011
Computations of the drag coefficients for low-Reynolds-number flow past rings
Publisher: Cambridge University Press (CUP)
Date: 10-03-2005
Feedback control system simulator for the control of biological cells in microfluidic cross slots and integrated microfluidic systems
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1LC20191C
Abstract: Control systems for lab on chip devices require careful characterisation and design for optimal performance. Traditionally, this involves either extremely computationally expensive simulations or lengthy iteration of laboratory experiments, prototype design, and manufacture. In this paper, an efficient control simulation technique, valid for typical microchannels, Computed Interpolated Flow Hydrodynamics (CIFH), is described that is over 500 times faster than conventional time integration techniques. CIFH is a hybrid approach, utilising a combination of pre-computed flows and hydrodynamic equations and allows the efficient simulation of dynamic control systems for the transport of cells through micro-fluidic devices. The speed-ups achieved by using pre-computed CFD solutions mapped to an n-dimensional control parameter space, significantly accelerate the evaluation and improvement of control strategies and chip design. Here, control strategies for a naturally unstable device geometry, the microfluidic cross-slot, have been simulated and optimal parameters have been found for proposed devices capable of trapping and sorting cells.
Preface to special issue of selected papers from CFD in the minerals and process industries
Publisher: Elsevier BV
Date: 04-2011
A coupled Landau model describing the Strouhal - Reynolds number profile of a three-dimensional circular cylinder wake
Publisher: AIP Publishing
Date: 23-07-2003
DOI: 10.1063/1.1597471
Abstract: A known bifurcation scenario describing the development and interaction of Mode A and Mode B vortex shedding modes of a circular cylinder wake is extended to predict the Strouhal–Reynolds number profile over the three-dimensional transitions. The mode litudes are described by coupled Landau equations and, with frequency information being included by the addition of complex coefficients, the model predicts the discontinuous nature of the Strouhal–Reynolds number shedding profile of the circular cylinder wake throughout the laminar three-dimensional transition regime. The model coefficients are determined from computations of the three-dimensional modes of a circular cylinder wake.
The effects of vortex breakdown bubbles on the mixing environment inside a base driven bioreactor
Publisher: Elsevier BV
Date: 04-2011
Probing horizontal convection instability via perturbation of the forcing boundary layer using a synthetic jet
Publisher: Elsevier BV
Date: 12-2016
Wake stability features behind a square cylinder: Focus on small incidence angles
Publisher: Elsevier BV
Date: 07-2011
The effect of rotation on radial horizontal convection and Nusselt number scaling in a cylindrical container
Publisher: Elsevier BV
Date: 10-2014
Stability of pulsatile quasi-two-dimensional duct flows under a transverse magnetic field
Publisher: American Physical Society (APS)
Date: 25-05-2021
Stability of flow in a channel with repeated flow-facing wedge-shaped protrusions
Publisher: Cambridge University Press (CUP)
Date: 10-05-2022
DOI: 10.1017/JFM.2022.200
Abstract: Motivated by an interest in inciting instabilities and mixing for heat transfer enhancement in ducts, flow in a channel with repeated wedge-shaped protrusions is considered for various blockage ratios (wedge height to duct height), pitch (distance between wedges) and wedge angles. The stability of the two-dimensional base flow and its dependence on the geometric parameters is elucidated through a global linear stability analysis. A linearly unstable two-dimensional mode was found, contrasting similar confined flow set-ups. However, the primary instability is a three-dimensional mode manifesting as counter-rotating streamwise vortices over the wedge tip. Analysis of the kinetic energy budget indicates a lift-up mechanism leading to instability, with the dominant energy gain of the global three-dimensional mode due to shear in the base flow. Structural sensitivity and receptivity of the instability to momentum forcing identifies the core of the instability and locations important for flow control. An endogeneity approach is used to show that the local perturbation pressure gradient component dominates the distribution of the local contribution to the growth rate of the linear global eigenmode in most cases considered, despite its net contribution being identically zero. Weakly nonlinear Stuart–Landau analysis reveals that the primary bifurcation is supercritical across all tested geometric parameter combinations. This is consistent with the finding of low linear transient growth lifications at subcritical Reynolds numbers, being orders of magnitude lower than in similar channel flow set-ups.
Natural convection heat transfer utilizing nanofluid in a cavity with a periodic side-wall temperature in the presence of a magnetic field
Publisher: Elsevier BV
Date: 05-2019
A centrifugal buoyancy formulation for Boussinesq‐type natural convection flows applied to the annulus cavity problem
Publisher: Wiley
Date: 09-2020
DOI: 10.1002/FLD.4904
Abstract: Traditionally, the Boussinesq approximation is adopted for numerical simulation of natural convection phenomena where density variations are supposed negligible except through the gravity term of the momentum equation. In this study, a recently developed formulation based on a Boussinesq approximation is presented in which the density variations are also considered in the advection terms. Extending density‐variations to the advection terms captures centrifugal effects arising from both bulk enclosure rotation and within in idual vortices, and thus more accurate results are expected. In this respect, the results of the proposed formulation are compared against the conventional Boussinesq simulations and weakly compressible approximation in the concentric horizontal annulus cavity. A new relation is established which maps the magnitude of the non‐Boussinesq parameter of incompressible flow to the corresponding relative temperature difference of a compressible flow simulation which is in agreement with the maximum allowed Gay‐Lussac number to avoid unphysical density values. For comparison purposes, variations of different thermo‐fluid parameters including average and local Nusselt number, entropy generation, and skin friction up to Ra = 10 5 are computed. Results obtained under the proposed approximation agree with the classical Boussinesq approximation up to Ra = 10 3 for large non‐Boussinesq parameter corresponding to the large relative temperature difference, but at Ra = 10 5 , computed thermo‐fluid parameters via the two approaches are not identical which justifies the inclusion of large Gay‐Lussac number for convection dominated regime in natural convection problems.
Short-wave instabilities on a vortex pair of unequal strength circulation ratio
Publisher: Elsevier BV
Date: 04-2011
Short-wave instability growth in closely spaced vortex pairs
Publisher: Inderscience Publishers
Date: 2010
Stability of the wakes of cylinders with triangular cross-sections
Publisher: Cambridge University Press (CUP)
Date: 12-04-2018
DOI: 10.1017/JFM.2018.161
Abstract: The stability of the wakes of cylinders with triangular cross-sections at incidence is investigated using Floquet stability analysis to elucidate the effects of cylinder inclination on the dominant flow instability. The upper limit of the Reynolds numbers (scaled by the height projected by the cylinder in this study) at which the wake of the two-dimensional base flow is time periodic is $Re\\approx 140$ for most cylinder inclinations, exceeding which the flow becomes aperiodic, restricting the range of Reynolds numbers permitted for the stability analysis. Two different instability modes are predicted to manifest as the first-occurring mode at various cylinder inclinations – a regular mode possessing perturbation structures consistent with mode A dominates the wakes of cylinders at inclinations $\\unicode[STIX]{x1D6FC}\\lesssim 34.6^{\\circ }$ and $\\unicode[STIX]{x1D6FC}\\gtrsim 55.4^{\\circ }$ , with a subharmonic mode consistent with mode C emerging as the primary mode in the wakes of the cylinder at the intermediate range of inclinations. For all inclinations, the mode B branch is not detected within the range of Reynolds numbers examined. The peak instability growth rates corresponding to mode A for all cylinder inclinations describe a linear variation with $(Re-Re_{A})/Re_{A}$ , where $Re_{A}$ is the mode A transition Reynolds number, while those corresponding to mode C vary only approximately linearly. The generalized trend most pertinently shows mode C to develop more rapidly than mode A at inclinations which permit it. Examination of the near wake of the two-dimensional time-periodic base flow demonstrates the dependence of the development and intensity of mode C on imbalances in the flow solution over each shedding period, directly implying that the two-dimensional base flow solutions deviate from the half-period-flip map as the cylinder inclination is increased. The degree of asymmetry of the two-dimensional base flow relative to the ideal half-period-flip map is quantified using several measures. The results show distinctly different trends in these asymmetry measures between inclinations where modes A or C are dominant, agreeing with results from the stability analysis. The nature of the predicted instability modes at transition are also investigated by applying the Stuart–Landau equation, showing the transitions to be supercritical for all cylinder inclinations, with mode C being consistently more strongly supercritical than mode A.
Heat transfer augmentation of a quasi-two-dimensional MHD duct flow via electrically driven vortices
Publisher: Informa UK Limited
Date: 20-09-2016
Related Organisations
Related Funding Activities
The Elusive Upper Bound Of Heat Transfer In Horizontal Convection
Start Date: 2015
End Date: 2017
Funder: Australian Research Council
View Funded ActivityHorizontal Convection At Ocean-relevant Proportions
Start Date: 2018
End Date: 2020
Funder: Australian Research Council
View Funded ActivityHybrid Imaging/modelling To Understand The Lung
Start Date: 2015
End Date: 2017
Funder: Australian Research Council
View Funded ActivityDiscovery Projects - Grant ID: DP150102240
Start Date: 03-2015
End Date: 11-2018
Amount: $334,400.00
Funder: Australian Research Council
View Funded ActivityDiscovery Projects - Grant ID: DP150102920
Start Date: 01-2015
End Date: 12-2017
Amount: $375,100.00
Funder: Australian Research Council
View Funded ActivityDiscovery Projects - Grant ID: DP120100153
Start Date: 01-2012
End Date: 06-2015
Amount: $320,000.00
Funder: Australian Research Council
View Funded ActivityDiscovery Projects - Grant ID: DP0665736
Start Date: 03-2006
End Date: 12-2006
Amount: $355,000.00
Funder: Australian Research Council
View Funded ActivityDiscovery Projects - Grant ID: DP0555897
Start Date: 2005
End Date: 04-2008
Amount: $338,000.00
Funder: Australian Research Council
View Funded ActivityDiscovery Projects - Grant ID: DP180102647
Start Date: 05-2018
End Date: 12-2022
Amount: $468,485.00
Funder: Australian Research Council
View Funded Activity