Kerry Hourigan

Monash University (Australia) · Department of Mechanical and Aerospace Engineering, Clayton

Flow transitions are an important fluid-dynamic phenomena for many reasons, including the direct effect on the aerodynamic forces acting on the body. In the present study, two-dimensional (2-D) and three-dimensional (3-D) wake transitions of a NACA0012 airfoil are studied for angles of attack in the range $0^\circ \leq \alpha \leq 20^\circ$ and Rey...

Anguilliform and carangiform fish have a thinner and thicker body along with a smaller and larger undulating wavelength-based kinematics for their propulsion, respectively. The present work is motivated by the fact that both types of fish are observed to adopt each other’s kinematics for a short duration on a needs basis. This study explores the ef...

We perform numerical simulations of the interaction between a vortex ring and a free surface, and provide a new interpretation of the mechanism by which the vortex ring connects to the free surface. Large vorticity gradients at the free surface result in the diffusion of surface-tangential vorticity out of the fluid. This is accompanied by the diff...

We present a decomposition of the streamwise fluid force for in-line vortex-induced vibration (VIV) to provide insight into how the wake drag acts as a driving force in fluid–structure interaction. This force decomposition is an extension of that proposed in the recent work of Konstantinidis et al. (J. Fluid Mech., vol. 907, 2021, p. A34), and is a...

This article presents a three-dimensional theory of vorticity creation on generalised interfaces, including both non-slip and free-slip boundaries, which generalises a previous two-dimensional formulation (Terrington et al. , J. Fluid Mech. , vol. 890, 2020, p. A5). Under this description, vorticity may be created on a boundary by the inviscid rela...

This study experimentally investigates the effect of structural damping on the transverse flow-induced vibration (FIV) of an elastically mounted circular cylinder under imposed axial rotation in a free stream. It has been shown by Wong et al. [K. W. L. Wong, J. Zhao, D. Lo Jacono, M. C. Thompson, and J. Sheridan, J. Fluid Mech. 829, 486 (2017)] tha...

Vortex-induced vibration (VIV) of an elastically mounted sphere placed close to or piercing a free surface (FS) was investigated numerically. The submergence depth ( $h$ ) was systematically varied between $1$ and $-$ 0.75 sphere diameters ( $D$ ) and the response simulated over the reduced velocity range $U^*\in [3.5,14]$ . The incompressible flow...

The observation of the leading-edge vortex (LEV) focused research into understanding its detailed role in insect and bird flight. A similar LEV-like structure is also observed in the near wake of a swimming fish, where the thrust force is of primary concern in contrast to the importance of the lift force for insect flight. However, compared with th...

A comprehensive two-dimensional numerical investigation has been undertaken to calculate the energetic cost of propulsion and the various flow transitions of a fish-like body undulation mechanism based on a National Advisory Committee for Aeronautics 0012 hydrofoil. This covers a wide range of Strouhal (0≤𝑆𝑡≤1.4) and Reynolds (500≤𝑅𝑒≤5000) numbers...

Fascinating wake vortex patterns emerge when a circular cylinder is forced to vibrate laterally to a uniform fluid flow, deviating from the well-known Kármán vortex street and first reported by Williamson & Roshko ( J. Fluids Struct. , vol. 2, 1988, pp. 355–381). The two rows of single vortices (2S mode) can suddenly transition to a row of paired v...

The present study examines the energy efficiency of self-propelled hydrofoils for various modes and kinematics of swimming adopted by various body-caudal fin fish. In particular, this work considers the intermittent burst-and-coast (B&C) and continuous swimming modes, and examines the effect of the undulating and/or pitching swimming kinematics, ad...

This review surveys the dramatic variations in wake structures and flow transitions, in addition to body forces, that appear as the motion of bluff bodies through a fluid occurs increasingly closer to a solid wall. In particular, we discuss the two cases of bluff bodies translating parallel to solid walls at varying heights and bluff bodies impacti...

Vorticity generation and conservation for two-dimensional interfaces and boundaries – ERRATUM - Volume 896 - M. Brøns, M. C. Thompson, T. Leweke, K. Hourigan

The generation and conservation of vorticity: deforming interfaces and boundaries in two-dimensional flows - Volume 890 - S. J. Terrington, K. Hourigan, M. C. Thompson

The flow-induced vibration of a tethered sphere was investigated through numerical simulations. A determination of the different modes of sphere vibration was made with simulations conducted at fixed Reynolds numbers (500, 1200 and 2000) with a sphere of mass ratio 0.8 over the reduced velocity range U* ∈ [3,32] . The flow was governed by the incom...

Flapping wings of insects can follow various complex-motion waveforms, influencing the flow structures over a wing and consequently the aerodynamic performance. However, most studies of insect-wing models incorporate either simple harmonic or robofly-like motion waveforms. The effects of other waveforms appear to be under-explored. Motivated by thi...

Direct numerical simulation of a counter-rotating vortex pair interacting with a wall - Volume 884 - Daniel Dehtyriov, Kerry Hourigan, Mark C. Thompson

The wing aspect ratio (AR), that is, the ratio of the wingspan to the mean wing chord, is the most important geometrical parameter describing an insect wing. While studies have shown that a change in AR affects the flow structure as well as the aerodynamic force components on wings, the reasons behind the wide variety of aspect ratios observed in n...

A study has been conducted to investigate the effect of angle of attack (α) on the hydrodynamic performance and wake structure of a static NACA0012 hydrofoil in a free-stream flow at low Reynolds number (Re). The investigation employed water-channel experiments and in-house numerical simulations (based on an immersed interface method) over the angl...

This study experimentally investigates the transverse flow-induced vibration (FIV) of an elastically mounted cube at three different incidence angles of α=0∘, 20∘ and 45∘, corresponding to two centreplane mirror-symmetric cases and one asymmetric case. The FIV response is characterised by analysing the vibration amplitude and frequency responses, t...

Flow-induced vibration (FIV) of a bluff body is a complex fluid-structure interaction (FSI) problem, for which analytical solutions generally don’t exist. Therefore, such problems generally need to be examined with experimental methods or computational simulations. Researchers have developed various numerical methodologies to solve FSI problems usi...

The flow over an insect wing can be highly influenced by the wing aspect ratio (A), affecting the aerodynamic forces. Previous studies present apparently contradictory effects of A, creating a challenge in selecting the optimum A in the design of insect-inspired micro air vehicles. Some recent studies indicate that the A-effects are coupled with th...

Wing shape is an important factor affecting the aerodynamic performance of wings of monocopters and flapping-wing micro air vehicles. Here, an evolutionary structural optimisation method is adapted to optimise wing shape to enhance the lift force due to aerodynamic pressure on the wing surfaces. The pressure distribution is observed to vary with th...

A new class of vibrations has been discovered where the vibrations are induced by forced sinusoidal rotary oscillation of a sphere. They have been termed Rotary-Induced Vibrations (RIV). RIV is observed only for selected forcing parameters, where the vibrations are locked to the forcing frequency. For these cases, the vibration amplitude increases...

Rotating bluff bodies are known to experience a side force due to a well-known phenomenon called the Mag-nus effect. The Magnus effect is evident in many sports (cricket, soccer, baseball, and football), where spinning balls are known to change their trajectories dramatically. In this study, we have experimentally investigated the effect of imposed...

In published literature of the vortex-induced vibration of a sphere, limited attention has been devoted to spheres having three degrees of freedom (DOF) motion and the effect on the vibration response. In this study, the vortex-induced vibration response of a 3-DOF elastically-mounted sphere was examined numerically. The response of a sphere allowe...

While the flow-induced vibration (FIV) of a circular cylinder has been characterised in considerable detail, the FIV of elliptical cylinders has not received similar attention. This study investigates the dynamic response of elastically-mounted elliptical cylinders with various cross-sectional aspect ratios (or elliptical ratios) in a free stream....

This study reports an experimental investigation on the flow-induced vibration (FIV) of elastically mounted rectangular cylinders with high-side-ratio in free-stream flow. The side ratio (σ), defined as the ratio of the cross-flow side width (h) to the streamwise side width (b) of the cylinder, namely σ=h∕b, was varied from 2.0 to 5.0. The fluid–st...

The individual and combined influences of aspect ratio ( $A$ ), Reynolds number ( $Re$ ) and Rossby number ( $Ro$ ) on the leading-edge vortex (LEV) of a rotating wing of insect-like planform are investigated numerically. A previous study from our group has determined the wingspan to be an appropriate length scale governing the large-scale LEV stru...

In the present study, a level-set immersed-boundary method based in-house code is used to study the effect of Strouhal number (0 – 1) on the flow pattern and engineering parameters for a NACA0012 hydrofoil undulating at a constant wavelength λ* = 1, maximum amplitude of undulation Amax = 0.1, and Reynolds number of 5000. Using a unified cause-and-e...

This experimental study investigates the effect of imposed rotary oscillation on the flow-induced vibration of a sphere that is elastically mounted in the cross-flow direction, employing simultaneous displacement, force and vorticity measurements. The response is studied over a wide range of forcing parameters, including the frequency ratio $f_{R}$...

While it has been known that an afterbody (i.e. the structural part of a bluff body downstream of the flow separation points) plays an important role affecting the wake characteristics and even may change the nature of the flow-induced vibration (FIV) of a structure, the question of whether an afterbody is essential for the occurrence of one partic...

Stable attachment of a leading-edge vortex (LEV) plays a key role in generating the high lift on rotating wings with a central body. The central body size can affect the LEV structure broadly in two ways. First, an overall change in the size changes the Reynolds number, which is known to have an influence on the LEV structure. Second, it may affect...

Results are presented from an experimental investigation into the effects of proximity to a free surface on vortex-induced vibration (VIV) experienced by fully and semi-submerged spheres that are free to oscillate in the cross-flow direction. The VIV response is studied over a wide range of reduced velocities: $3\leqslant U^{\ast }\leqslant 20$ , c...

This study experimentally investigates the in-line flow-induced vibration (FIV) of an elastically mounted circular cylinder under forced axial rotation in a free stream. The present experiments characterise the structural vibration, fluid forces and wake structure of the fluid–structure system at a low mass ratio (the ratio of the total mass to the...

The effects of transverse rotation on the vortex-induced vibration (VIV) of a sphere in a uniform flow are investigated numerically. The one degree-of-freedom sphere motion is constrained to the cross-stream direction, with the rotation axis orthogonal to flow and vibration directions. For the current simulations, the Reynolds number of the flow, $...

Discrepancies exist in the effects of aspect ratio on the lift coefficient (CL) of insect wings reported in past studies. CL is found to be affected by the aspect ratio, Reynolds number and Rossby number - studied over a large parameter space. The large scale vortex structure over a wing is found to scale with the wing span. The Reynolds number and...

Vortex-induced vibration (VIV) of a sphere represents one of the most generic fundamental fluid–structure interaction problems. Since vortex-induced vibration can lead to structural failure, numerous studies have focused on understanding the underlying principles of VIV and its suppression. This paper reports on an experimental investigation of the...

Flow-induced vibration of an elastically mounted sphere was investigated computationally for the classic case where the sphere motion was constrained to move in a direction transverse to the free stream. This study, therefore, provides additional insight into, and comparison with, corresponding experimental studies of transverse motion, and distinc...

This paper presents the characteristics of the different stages in the evolution of the wake of a circular cylinder rolling without slipping along a wall at constant speed, acquired through numerical stability analysis and two- and three-dimensional numerical simulations. Reynolds numbers between 30 and 300 are considered. Of importance in this stu...

The wake of an elliptical cylinder at low incident angles is investigated for different aspect ratio ( $\unicode[STIX]{x1D6E4}=\text{major:minor axis ratio}$ ) cylinders using stability analysis and direct simulations. In particular, two- and three-dimensional transitions are mapped for cylinders of aspect ratios between 1 and 4 using Floquet stabi...

The stable attachment of a leading-edge vortex (LEV) is responsible for the high lift observed from insect wings. In experiments, we study the flow structure over a model wing mounted on a central body. The diameter of the central body and the change in Rossby number (Ro) due to placement of the wing root away from the centre can affect the flow st...

Pluripotent stem cells have generated a great deal of excitement concerning their use for clinical therapy and regenerative medicine. Similar to other mammalian cells, the growth of these cells is dependent on various culture conditions. The presence of lactic acid as a metabolic by-product has been reported to be detrimental for mammalian cells in...

A numerical study of flow past a cylinder oscillating transverse, inline and at 45◦ to the incoming flow was performed at Re = 100. The forcing frequency ratio F and the forcing amplitude ratio A ∗ were varied independently first by fixing A ∗ = 0.2 and varying F from 0.1 to 2.5 and then fixing F = 0.5 and varying A ∗ from 0.1 to 1. Good agreement...

A recent approach to colon cancer therapy is to employ selective drugs with specific extra/intracellular sites of action. Alteration of cytoskeletal protein reorganization and, subsequently, to cellular biomechanical behaviour during cancer progression highly affects the cancer cell progress. Hence, cytoskeleton targeted drugs are an important clas...

With the aim of understanding discrepancies between experimental observations and numerical simulations for a cylinder rolling down an inclined plane, this study investigates the effect that offsetting the centre-of-mass from the cylinder centroid has on body forces, velocity and wake structures. The numerical cases considered focus on the same par...

Linear stability analysis of a wide range of two-dimensional and axisymmetric bluff-body wakes shows that the first three-dimensional mode to became unstable is always mode E. From the studies presented in this paper, it is speculated to be the universal primary 3D instability, irrespective of the flow configuration. However, since it is a transiti...

A microfluidics approach to synthesize core-shell nanocarriers with highly pH tunability is described. The sacrificial shell protects the core layer with the drugs and prevents their release in the severe pH conditions of the gastrointestinal tract, while allowing for drug release in the proximity of a tumor. Proposed nanoparticulate drug delivery...

Stable attachment of the Leading Edge Vortex (LEV) is a peculiar aspect of aerodynamics of flapping wings of insects providing much higher lift than that from the aircraft wings. Parameters such as wing aspect ratio (AR), Reynolds number (Re), advance ratio and wing flexibility play an important role in determining the stability of a LEV. In our pr...

Stable attachment of the Leading Edge Vortex (LEV) is responsible for stable flight in insects. The LEV structure over a flapping insect wing is influenced by several geometrical and kinematic parameters. In our study, it is shown that a change in the wing Reynolds number (Re) affects the LEV structure. A comparison with previous numerical results...

It is estimated that by 2030, almost 23.6 million people will perish from cardiovascular disease, according to the WHO. The review discusses advances in stem cell therapy for myocardial infarction, including cell sources, methods of differentiation, expansion selection and their route of delivery. Skeletal muscle cells, hematopoietic cells and mese...

The flow past a rotating circular cylinder translating parallel to a wall at different heights is investigated for Reynolds numbers up to 400 for three discrete rotation rates. In particular, the various wake transitions that occur as a function of gap height are quantified for the three cases examined: non-rotation, and forward and reverse rotatio...

Recent experimental research on rotating cylinder wakes has found that a previously numerically predicted subharmonic instability mode, mode C, occurs for considerably lower rotation rates than predicted through stability analysis, yet other mode transitions occur closer to the predicted onset. One difference between the theoretical and experimenta...

The types of vortex breakdown observed in the torsionally driven cylinder (TDC) flow and in the flow through an open-ended pipe are compared. The connection between the various breakdown types is specifically addressed, and the differences in manifestation of breakdown are attributed to the different Reynolds number regimes involved. Here, in both...

Cardiovascular diseases remain the major cause of mortality worldwide. Pathologies of the vasculature such as atherosclerosis are often related to biochemical and genetic factors, as well as mechanical effects that strongly change the function and shape of arteries. The present work is part of a general research project that aims to understand bett...

Redox-active stimuli have gained a great deal of interest as an indicating factor for designing bioresponsive matrices in gene delivery. Hence, a wide range of gene carriers has been designed incorporating the redox-stimuli characteristics. The most important type of gene carriers is the class of redox responsive polymers. Among them, disulfide inc...

The generation, redistribution and, importantly, conservation of vorticity and circulation is studied for incompressible Newtonian fluids in planar and axisymmetric geometries. A generalised formulation of the vorticity at the interface between two fluids for both no-slip and stress-free conditions is presented. Illustrative examples are provided f...

We present detailed quantitative measurement analyses for flow in a spinner flask with spinning rates between 20 to 45 RPM, utilizing the optical velocimetry measurement technique of Particle Image Velocimetry (PIV). A partial section of the impeller was immersed in the working fluid to reduce the shear forces induced on the cells cultured on micro...

The spinner flask bioreactor has been widely used in in vitro cell culturing processes due to its superiority in providing a homogeneous culture environment compared to traditional culturing methods. However, there is limited understanding of the flow fields in these bioreactors, and optimum culture conditions are yet to be determined. This article...

Atherosclerosis is a progressive disease, involving the build-up of lipid streaks in artery walls, leading to plaques. Understanding the development of atherosclerosis and plaque vulnerability is critically important since plaque rupture can result in heart attack or stroke. Plaques can be divided into two distinct types: those likely to rupture (v...

Hydrogel-forming materials that mimic the three-dimensional architecture and properties of tissue are known to have a positive effect on cellular differentiation and growth. A subset of those are in situ gels, which utilise in vivo conditions like pH, for example, acetate phthalate; temperature, for example, poloxamer; ionic concentration, for exam...

In recent times, the study and use of induced pluripotent stem cells (iPSC) have become important in order to avoid the ethical issues surrounding the use of embryonic stem cells. Therapeutic, industrial and research based use of iPSC requires large quantities of cells generated in vitro. Mammalian cells, including pluripotent stem cells, have been...

While the wake of a circular cylinder and, to a lesser extent, the normal flat plate have been studied in considerable detail, the wakes of elliptic cylinders have not received similar attention. However, the wakes from the first two bodies have considerably different characteristics, in terms of three-dimensional transition modes, and near- and fa...