ORCID Profile
0000-0002-7089-9686
Current Organisation
Monash University
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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 | Mechanical Engineering | Turbulent Flows | Fluidisation and Fluid Mechanics | Combustion And Fuel Engineering | Climate Change Processes | Aerodynamics | Atmospheric Sciences | Fluidization And Fluid Mechanics | Theoretical and Computational Chemistry not elsewhere classified | Mechanical Engineering not elsewhere classified | Interdisciplinary Engineering Not Elsewhere Classified | Nanotechnology | Pharmaceutical Sciences | Pharmacology and Pharmaceutical Sciences | Evolutionary Biology not elsewhere classified | Condensed Matter Physics not elsewhere classified | Nanotechnology | Engineering/Technology Instrumentation | Soil And Water Sciences Not Elsewhere Classified | Composite and Hybrid Materials | Mathematical Physics | Structural Engineering | Aerodynamics (excl. Hypersonic Aerodynamics) | Energy Generation, Conversion and Storage Engineering | Solid Mechanics | Materials Engineering Not Elsewhere Classified | Particle Physics | Tectonics | Optical Properties of Materials | Respiratory Diseases | Heat And Mass Transfer Operations | Resources Engineering and Extractive Metallurgy not elsewhere classified | Pharmaceutical Sciences And Pharmacy | Mechanical Engineering | Robotics And Mechatronics | Theoretical Physics | Photonics, Optoelectronics and Optical Communications | Galactic Astronomy | Biomechanical Engineering | Geophysical Fluid Dynamics | Enzymes | Computational Fluid Dynamics | Heat and Mass Transfer Operations | Condensed Matter Modelling and Density Functional Theory | Bioinformatics |
ANZSRC Socio-Economic Objective (SEO)
Physical sciences | Expanding Knowledge in the Physical Sciences | Renewable energy not elsewhere classified (e.g. geothermal) | Climate Change Models | Renewable energy | Expanding Knowledge in the Chemical Sciences | Transport | Air Force | Other | Air Force | Respiratory System and Diseases (incl. Asthma) | Expanding Knowledge in the Medical and Health Sciences | Commercial Energy Conservation and Efficiency | Expanding Knowledge in the Biological Sciences | Atmospheric Processes and Dynamics | Wind Energy | Ground transport | Land and water management | Fabricated metal products not elsewhere classified | Other | Human pharmaceutical products | Behavioural and cognitive sciences | Environmental health | Human Pharmaceutical Products not elsewhere classified | Navy | Wind | Civil Construction Design | Materials performance and processes | Antarctic and Sub-Antarctic Oceanography | Land and water management | Air transport | Automotive equipment | Aerospace equipment | Mathematical sciences | Nautical equipment | Oil and Gas Extraction | Cardiovascular System and Diseases | Respiratory system and diseases (incl. asthma) | Coated Metal and Metal-Coated Products | Effects of Climate Change and Variability on Australia (excl. Social Impacts) | Climate Change Mitigation Strategies | Energy transformation | Industrial instrumentation | Medical instrumentation | Aerospace Transport not elsewhere classified | Expanding Knowledge in Technology | Scientific instrumentation | Industrial Energy Conservation and Efficiency | Energy Conservation and Efficiency in Transport | Aerospace Equipment | Expanding Knowledge in the Environmental Sciences | Expanding Knowledge in the Earth Sciences | Automotive Equipment | Nautical Equipment (excl. Yachts) | Expanding Knowledge in Engineering | Expanding Knowledge in the Agricultural and Veterinary Sciences | Machinery and equipment not elsewhere classified
Related Links
Publications
Analysis of the anisotropy of group velocity error due to spatial finite difference schemes from the solution of the 2D linear Euler equations
Publisher: Wiley
Date: 15-05-2012
DOI: 10.1002/FLD.3683
A novel 4D digital holographic PIV/PTV (4D-DHPIV/PTV) methodology using iterative predictive inverse reconstruction
Publisher: IOP Publishing
Date: 20-07-2020
Coupling modes of an underexpanded twin axisymmetric jet
Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 09-2018
DOI: 10.2514/1.J056434
Efficiency of the lumped parameter concept and the role of liquid properties in modelling microdroplet evaporation
Publisher: Elsevier BV
Date: 02-2016
Flow around a hemisphere-cylinder at high angle of attack and low Reynolds number. Part II: POD and DMD applied to reduced domains
Publisher: Elsevier BV
Date: 07-2015
Turbulence structures of wall-bounded shear flows found using DNS data
Publisher: Cambridge University Press (CUP)
Date: 25-02-1998
DOI: 10.1017/S0022112097008057
Abstract: This work extends the study of the structure of wall-bounded flows using the topological properties of eddying motions as developed by Chong et al . (1990), Soria et al . (1992, 1994), and as recently extended by Blackburn et al . (1996) and Chacin et al . (1996). In these works, regions of flow which are focal in nature are identified by being enclosed by an isosurface of a positive small value of the discriminant of the velocity gradient tensor. These regions resemble the attached vortex loops suggested first by Theodorsen (1955). Such loops are incorporated in the attached-eddy model versions of Perry & Chong (1982), Perry et al . (1986), and Perry & Marusic (1995), which are extensions of a model first formulated by Townsend (1976). The direct numerical simulation (DNS) data of wall-bounded flows studied here are from the zero-pressure-gradient flow of Spalart (1988) and the boundary layer with separation and reattachment of Na & Moin (1996). The flow structures are examined from the viewpoint of the attached eddy hypothesis.
The stability of low Reynolds number round jets
Publisher: Springer Science and Business Media LLC
Date: 23-01-2004
Three-dimensional instabilities over a rectangular open cavity: from linear stability analysis to experimentation
Publisher: Cambridge University Press (CUP)
Date: 28-04-2014
DOI: 10.1017/JFM.2014.126
Abstract: Three-dimensional instabilities arising in open cavity flows are responsible for complex broad-banded dynamics. Existing studies either focus on theoretical properties of ideal simplified flows or observe the final state of experimental flows. This paper aims to establish a connection between the onset of the centrifugal instabilities and their final expression within the fully saturated flow. To that end, a linear three-dimensional modal instability analysis of steady two-dimensional states developing in an open cavity of aspect ratio $L/D=2$ (length over depth) is conducted. This analysis is performed together with an experimental study in the same geometry adding spanwise endwalls. Two different Reynolds numbers are investigated through spectral analyses and modal decomposition. The physics of the flow is thoroughly described exploiting the strengths of each methodology. The main flow structures are identified and salient space and time scales are characterised. Results indicate that the structures obtained from linear analysis are mainly consistent with the fully saturated experimental flow. The analysis also brings to light the selection and alteration of certain wave properties, which could be caused by nonlinearities or the change of spanwise boundary conditions.
Author response: Flagellar energetics from high-resolution imaging of beating patterns in tethered mouse sperm
Publisher: eLife Sciences Publications, Ltd
Date: 03-2021
On the coherent structures and stability properties of a leading-edge separated aerofoil with turbulent recirculation
Publisher: Cambridge University Press (CUP)
Date: 19-08-2011
DOI: 10.1017/JFM.2011.285
Abstract: The present study is motivated by a need to produce stability modes to assist in the understanding and control of unsteady separated flows. The flow configuration is a NACA 0015 aerofoil with laminar leading-edge separation and turbulent recirculation. In previous water tunnel experiments, this flow configuration was measured in an unperturbed (uncontrolled) separated state, and a harmonically perturbed (controlled) reattached state. This study presents numerical data of the unperturbed case, and recovers stability modes to describe the evolution of perturbations in this environment. The unperturbed flow is numerically generated using large eddy simulation. Its temporal properties are quantified via a Fourier analysis of the velocity time history at selected points in space. The leading-edge shear layer instability is characterized by instantaneous vortex structures, and the bluff body shedding is illustrated by proper orthogonal decomposition modes. Statistical measures of the velocity field agree well with the water tunnel measurements. Finally a stability analysis is undertaken using a triple decomposition to distinguish between the time averaged field, the unsteady scales of motion, and a coherent wave (perturbation). This analysis identifies that perturbations in the region immediately downstream of the separated shear layer have the highest spatial growth rates. The associated frequency is of the order of the sub-harmonic of the shear layer instability.
The organization of near-wall turbulence: a comparison between boundary layer SPIV data and channel flow DNS data
Publisher: Informa UK Limited
Date: 2010
CRISPs Function to Boost Sperm Power Output and Motility
Publisher: Frontiers Media SA
Date: 05-08-2021
DOI: 10.3389/FCELL.2021.693258
Abstract: Fertilization requires sperm to travel long distances through the complex environment of the female reproductive tract. Despite the strong association between poor motility and infertility, the kinetics of sperm tail movement and the role in idual proteins play in this process is poorly understood. Here, we use a high spatiotemporal sperm imaging system and an analysis protocol to define the role of CRISPs in the mechanobiology of sperm function. Each of CRISP1, CRISP2, and CRISP4 is required to optimize sperm flagellum waveform. Each plays an autonomous role in defining beat frequency, flexibility, and power dissipation. We thus posit that the expansion of the CRISP family from one member in basal vertebrates, to three in most mammals, and four in numerous rodents, represents an ex le of neofunctionalization wherein proteins with a common core function, boosting power output, have evolved to optimize different aspects of sperm tail performance.
The accuracy of tomographic particle image velocimetry for measurements of a turbulent boundary layer
Publisher: Springer Science and Business Media LLC
Date: 25-11-2010
Direct numerical simulation of a self-similar adverse pressure gradient turbulent boundary layer
Publisher: Elsevier BV
Date: 10-2016
Turbulent cylinder-stirred flow heat and momentum transfer research in batch operated single-phase square reactor
Publisher: Elsevier BV
Date: 02-2022
Interaction of Shear Layer Coherent Structures and the Stand-Off Shock of an Under-Expanded Circular Impinging Jet
Publisher: Springer Berlin Heidelberg
Date: 18-12-2015
Use of holography in particle image velocimetry measurements of a swirling flow
Publisher: Springer Science and Business Media LLC
Date: 03-08-1999
High spatial range velocity measurements in a high Reynolds number turbulent boundary layer
Publisher: AIP Publishing
Date: 02-2014
DOI: 10.1063/1.4866458
Abstract: Here, we detail and analyse a multi-resolution particle image velocity measurement that resolves the wide range of scales prevalent in a zero pressure gradient turbulent boundary layer at high Reynolds numbers (up to Reτ ≈ 20 000). A unique configuration is utilised, where an array of eight high resolution cameras at two magnification levels are used simultaneously to obtain a large field of view, while still resolving the smaller scales prevalent in the flow. Additionally, a highly magnified field of view targeted at the near wall region is employed to capture the viscous sublayer and logarithmic region, with a spatial resolution of a few viscous length scales. Flow statistics from these measurements show good agreement with prior, well resolved hot-wire anemometry measurements. Analysis shows that the instantaneous wall shear stress can be reliably computed, which is historically known to be challenging in boundary layers. A statistical assessment of the wall shear stress shows good agreement with existing correlations, prior experimental and direct numerical simulation data, extending this view to much higher Reynolds numbers. Furthermore, conditional analysis using multiple magnification levels is detailed, to study near-wall events associated with high skin friction fluctuations and their associated overlaying structures in the log region. Results definitively show that the passage of very large-scale positive (or negative) velocity fluctuations are associated with increased (or reduced) small-scale variance in wall shear stress fluctuations.
A simple-to-fabricate composite convective heat-transfer test surface
Publisher: Elsevier BV
Date: 1990
Three-dimensional density measurements of a heated jet using laser-speckle tomographic background-oriented schlieren
Publisher: Elsevier BV
Date: 04-2023
Dynamic stall in vertical axis wind turbines: Comparing experiments and computations
Publisher: Elsevier BV
Date: 11-2015
Time-resolved PIV measurements of the flow field in a stenosed, compliant arterial model
Publisher: Springer Science and Business Media LLC
Date: 05-2013
Analysis of a Turbulent Boundary Layer Subjected to a Strong Adverse Pressure Gradient
Publisher: IOP Publishing
Date: 16-04-2014
Skin-friction critical points in wall-bounded flows
Publisher: IOP Publishing
Date: 16-04-2014
Laser-based planar imaging of nano-particle fluidization: Part II—mechanistic analysis of nanoparticle aggregation
Publisher: Elsevier BV
Date: 12-2006
Topological visualisation of focal structures in free shear flows
Publisher: Springer Science and Business Media LLC
Date: 12-1994
DOI: 10.1007/BF00849111
Examination of the flow around a hot-wire probe using particle image velocimetry
Publisher: Springer Science and Business Media LLC
Date: 10-1995
DOI: 10.1007/BF00190254
Measurements of Near Wall Velocity and Wall Stress in a Wall-Bounded Turbulent Flow Using Digital Holographic Microscopic PIV and Shear Stress Sensitive Film
Publisher: Springer Netherlands
Date: 2011
An improved interpolation scheme for finite volume simulations on unstructured meshes
Publisher: American Mathematical Society (AMS)
Date: 14-11-2012
A varying-swirl design concept for dry powder inhalers
Publisher: Elsevier BV
Date: 06-2023
Measuring unsteady drag of the flow around a sphere based on time series displacement measurements using physics-informed neural networks
Publisher: Elsevier BV
Date: 06-2023
Flow visualization of the effect of pitch amplitude changes on the vortical signatures behind a three-dimensional flapping airfoil
Publisher: SPIE
Date: 28-04-2003
DOI: 10.1117/12.509776
High Resolution PIV Study of Zero-Net-Mass-Flow Lift Enhancement of NACA 0015 Airfoil at High Angles of Attack
Publisher: Springer Netherlands
Date: 2008
Extensive characterisation of a high Reynolds number decelerating boundary layer using advanced optical metrology
Publisher: Informa UK Limited
Date: 29-06-2017
High-speed optical measurements of an underexpanded supersonic jet impinging on an inclined plate
Publisher: SPIE
Date: 28-11-2008
DOI: 10.1117/12.822137
Interaction of a supersonic underexpanded jet with a flat plate
Publisher: Springer Berlin Heidelberg
Date: 18-12-2016
Light-field camera-based 3D volumetric particle image velocimetry with dense ray tracing reconstruction technique
Publisher: Springer Science and Business Media LLC
Date: 05-06-2017
Accuracy of out-of-plane vorticity measurements derived from in-plane velocity field data
Publisher: Springer Science and Business Media LLC
Date: 19-10-1998
Shock structures and instabilities formed in an underexpanded jet impinging on to cylindrical sections
Publisher: Springer Science and Business Media LLC
Date: 12-03-2015
Receptivity characteristics of under-expanded supersonic impinging jets
Publisher: Cambridge University Press (CUP)
Date: 26-02-2020
DOI: 10.1017/JFM.2020.63
A study of unsteady laminar boundary layer flow on a flat plate using a smoke-wire/silhoutte flow visualization technique
Publisher: Elsevier BV
Date: 05-1990
Unraveling the Kinematics of Sperm Motion by Reconstructing the Flagellar Wave Motion in 3D
Publisher: Wiley
Date: 09-02-2022
Abstract: Sperm swim through the female reproductive tract by propagating a 3D flagellar wave that is self‐regulatory in nature and driven by dynein motors. Traditional microscopy methods fail to capture the full dynamics of sperm flagellar activity as they only image and analyze sperm motility in 2D. Here, an automated platform to analyze sperm swimming behavior in 3D by using thin‐lens approximation and high‐speed dark field microscopy to reconstruct the flagellar waveform in 3D is presented. It is found that head‐tethered mouse sperm exhibit a rolling beating behavior in 3D with the beating frequency of 6.2 Hz using spectral analysis. The flagellar waveform bends in 3D, particularly in the distal regions, but is only weakly nonplanar and ambidextrous in nature, with the local helicity along the flagellum fluctuating between clockwise and counterclockwise handedness. These findings suggest a nonpersistent flagellar helicity. This method provides new opportunities for the accurate measurement of the full motion of eukaryotic flagella and cilia which is essential for a biophysical understanding of their activation by dynein motors.
Particle relaxation and its influence on the particle image velocimetry corss-correlation function
Publisher: Springer Science and Business Media LLC
Date: 17-05-2011
Evaluation of a film-based wall shear stress measurement technique in a turbulent channel flow
Publisher: Elsevier BV
Date: 2016
Development of a nonlinear eddy-viscosity closure for the triple-decomposition stability analysis of a turbulent channel
Publisher: Cambridge University Press (CUP)
Date: 08-10-2010
DOI: 10.1017/S0022112010003617
Abstract: The analysis of the instabilities in an unsteady turbulent flow is undertaken using a triple decomposition to distinguish between the time-averaged field, a coherent wave and the remaining turbulent scales of motion. The stability properties of the coherent scale are of interest. Previous studies have relied on prescribed constants to close the equations governing the evolution of the coherent wave. Here we propose an approach where the model constants are determined only from the statistical measures of the unperturbed velocity field. Specifically, a nonlinear eddy-viscosity model is used to close the equations, and is a generalisation of earlier linear eddy-viscosity closures. Unlike previous models the proposed approach does not assume the same dissipation rate for the time- and phase-averaged fields. The proposed approach is applied to a previously published turbulent channel flow, which was harmonically perturbed by two vibrating ribbons located near the channel walls. The response of the flow was recorded at several downstream stations by phase averaging the probe measurements at the same frequency as the forcing. The experimentally measured growth rates and velocity profiles, are compared to the eigenvalues and eigenvectors resulting from the stability analysis undertaken herein. The modes recovered from the solution of the eigenvalue problem, using the nonlinear eddy-viscosity model, are shown to capture the experimentally measured spatial decay rates and mode shapes of the coherent scale.
Multimodal instability in the weakly underexpanded elliptic jet
Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 09-2015
DOI: 10.2514/1.J053738
Analysis of Coherent Structures in an Under-Expanded Supersonic Impinging Jet Using Spectral Proper Orthogonal Decomposition (SPOD)
Publisher: MDPI AG
Date: 06-07-2018
Distortion correction of two-component two-dimensional PIV using a large imaging sensor with application to measurements of a turbulent boundary layer flow at $$\hbox {Re}_{\tau } = 2386$$
Publisher: Springer Science and Business Media LLC
Date: 14-08-2021
The Temporal Coherence of Prograde and Retrograde Spanwise Vortices in Zero-Pressure Gradient Turbulent Boundary Layers
Publisher: Springer International Publishing
Date: 18-08-2015
Combustion properties of slow pyrolysis bio-oil produced from indigenous Australian species
Publisher: Elsevier BV
Date: 10-2006
Improved Drainage Cannula Design to Reduce Thrombosis in Veno-Arterial Extracorporeal Membrane Oxygenation
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 20-04-2021
DOI: 10.1097/MAT.0000000000001440
Abstract: Thrombosis is a potentially life-threatening complication in veno-arterial extracorporeal membrane oxygenation (ECMO) circuits, which may originate from the drainage cannula due to unfavorable blood flow dynamics. This study aims to numerically investigate the effect of cannula design parameters on local fluid dynamics, and thus thrombosis potential, within ECMO drainage cannulas. A control cannula based on the geometry of a 17 Fr Medtronic drainage cannula concentrically placed in an idealized, rigid-walled geometry of the right atrium and superior and inferior vena cava was numerically modeled. Simulated flow dynamics in the control cannula were systematically compared with 10 unique cannula designs which incorporated changes to side hole diameter, the spacing between side holes, and side hole angles. Local blood velocities, maximum wall shear stress (WSS), and blood residence time were used to predict the risk of thrombosis. Numerical results were experimentally validated using particle image velocimetry. The control cannula exhibited low blood velocities (59 mm/s) at the cannula tip, which may promote thrombosis. Through a reduction in the side hole diameter (2 mm), the spacing between the side holes (3 mm) and alteration in the side hole angle (30° relative to the flow direction), WSS was reduced by 52%, and cannula tip blood velocity was increased by 560% compared to the control cannula. This study suggests that simple geometrical changes can significantly alter the risk of thrombosis in ECMO drainage cannulas.
Volumetric measurements of a self-similar adverse pressure gradient turbulent boundary layer using single-camera light-field particle image velocimetry
Publisher: Springer Science and Business Media LLC
Date: 13-08-2019
Laminar boundary layer receptivity to transverse structural vibration
Publisher: Elsevier BV
Date: 09-1995
The largest diameter of falling drop in the up-gas flow
Publisher: Elsevier BV
Date: 02-2023
Dynamic stall in vertical axis wind turbines: scaling and topological considerations
Publisher: Cambridge University Press (CUP)
Date: 27-02-2018
DOI: 10.1017/JFM.2018.112
Abstract: Vertical axis wind turbine blades are subject to rapid, cyclical variations in angle of attack and relative airspeed which can induce dynamic stall. This phenomenon poses an obstacle to the greater implementation of vertical axis wind turbines because dynamic stall can reduce turbine efficiency and induce structural vibrations and noise. This study seeks to provide a more comprehensive description of dynamic stall in vertical axis wind turbines, with an emphasis on understanding its parametric dependence and scaling behaviour. This problem is of practical relevance to vertical axis wind turbine design but the inherent coupling of the pitching and velocity scales in the blade kinematics makes this problem of more broad fundamental interest as well. Experiments are performed using particle image velocimetry in the vicinity of the blades of a straight-bladed gyromill-type vertical axis wind turbine at blade Reynolds numbers of between 50 000 and 140 000, tip speed ratios between $\\unicode[STIX]{x1D706}=1$ to $\\unicode[STIX]{x1D706}=5$ , and dimensionless pitch rates of $0.10\\leqslant K_{c}\\leqslant 0.20$ . The effect of these factors on the evolution, strength and timing of vortex shedding from the turbine blades is determined. It is found that tip speed ratio alone is insufficient to describe the circulation production and vortex shedding behaviour from vertical axis wind turbine blades, and a scaling incorporating the dimensionless pitch rate is proposed.
High resolution Cross-Correlation PIV on photographic film
Publisher: SPIE
Date: 29-09-1998
DOI: 10.1117/12.323370
Stability Analysis of Time-averaged Jet Flows: Fundamentals and Application
Publisher: Elsevier BV
Date: 2015
Experimental analysis of particle sizes for PIV measurements
Publisher: IOP Publishing
Date: 11-08-2016
Experimental evidence of near-wall reverse flow events in a zero pressure gradient turbulent boundary layer
Publisher: Elsevier BV
Date: 02-2018
Experimental investigation using micro-PIV of the effect of microRNA-1 deficiency on motility in Caenorhabditis elegans
Publisher: Cold Spring Harbor Laboratory
Date: 16-06-2020
DOI: 10.1101/2020.06.16.119396
Abstract: Caenorhabditis elegans is a microscopic nematode used extensively as a model organism in studies of neuromuscular function and neurodegenerative disorders. A mutation in mir-1 affects signalling at the neuromuscular junction. We investigate the effect of this mutation on the propulsive power exerted by nematodes as they grow in size with age. We compare the motility of wild-type and mir-1(gk276) mutant nematodes in a Newtonian fluid using a two-component, two dimensional (2C-2D) Digital Microscopic Particle Image Velocimetry ( µ -PIV) technique. Beating litudes of the head and tail, the wavelength of undulatory waves and the swimming speed scale linearly with size in both the wild-type and mutant strains. The beating frequency is independent of size or position along the body. Differences in the magnitudes of these kinematic parameters between the two strains, however, grow systematically with age. The swimming speed scales linearly with the wave speed of the neuromuscular undulation in both nematode strains with a conserved ratio. The magnitude of mean power and mean local fluid circulation in the mutant is significantly lower compared to those of the wild-type animals of the same age. This indicates that a mutation in mir-1 adversely affects motility in C. elegans .
Investigating Shear-Layer Instabilities in Supersonic Impinging Jets Using Dual-Time Particle Image Velocimetry
Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 06-2022
DOI: 10.2514/1.J061342
Evolution of the turbulent/non-turbulent interface of an axisymmetric turbulent jet
Publisher: Springer Science and Business Media LLC
Date: 2013
Computationally efficient storage of 3D particle intensity and position data for use in 3D PIV and 3D PTV
Publisher: IOP Publishing
Date: 25-09-2013
Laser-based planar imaging of nano-particle fluidization: Part I—determination of aggregate size and shape
Publisher: Elsevier BV
Date: 08-2006
Staging behaviour in screeching elliptical jets
Publisher: SAGE Publications
Date: 11-2015
DOI: 10.1260/1475-472X.14.7.1005
Abstract: The staging behaviour of jet screech in an elliptical nozzle with with an aspect ratio AR = 2.0 is examined across a range of pressure ratios. Acoustic measurements and high resolution imaging are used to assess the staging behaviour. Based on the frequency of the dominant screech tone, the jet staging behaviour can be separated into five distinct modes over the range of pressures studied. A statistical analysis of the schlieren images suggests that the first mode is varicose, the next three modes are flapping instabilities, and the final mode is helical in nature. A comparison of characteristic length scales in the jet is undertaken to explain the mode switches. A shift from the classical “weakest link” feedback model to an acoustic waveguide model, associated with a shift in characteristic length scale of the jet, is used to explain the discontinuous jumps in screech tone frequency. The results indicate that the different acoustic feedback mechanisms need not necessarily be associated with a particular instability mode shape.
Effect of turbulence on drop breakup in counter air flow
Publisher: Elsevier BV
Date: 11-2019
A study of the three-term hot-wire system equation and analog linearization based on it
Publisher: Elsevier BV
Date: 05-1990
High-speed visualisation of primary break-up of an annular liquid sheet
Publisher: Springer Science and Business Media LLC
Date: 08-2007
Axial plus tangential entry swirling jet
Publisher: Springer Science and Business Media LLC
Date: 16-09-2009
Three-dimensional instabilities over a rectangular open cavity: from linear stability analysis to experimentation – ERRATUM
Publisher: Cambridge University Press (CUP)
Date: 27-06-2014
DOI: 10.1017/JFM.2014.334
On the modulating effect of three-dimensional instabilities in open cavity flows
Publisher: Cambridge University Press (CUP)
Date: 30-10-2014
DOI: 10.1017/JFM.2014.576
Abstract: Open cavity flows are known to select and enhance locked-on modes or tones. High-energy self-sustained oscillations arise within the shear layer, impinging onto the trailing edge of the cavity. These self-sustained oscillations are subject to litude modulations (AMs) at multiple low frequencies. However, only a few studies have addressed the identification of the lowest modulating frequencies. The present work brings to light salient AMs of the shear layer waves and identifies their source as three-dimensional dynamics existing inside the cavity. Indeed, the recirculating inner flow gives rise to centrifugal instabilities, which entail broad-band frequencies down two orders of magnitude lower than those of the self-sustained oscillations. Using time-resolved PIV (TRPIV) in two planes, the nonlinearly saturated dynamics is analysed in both space and time by means of proper orthogonal decomposition, global Fourier decomposition and Hilbert–Huang transforms. The inner flow can be decomposed as three-dimensional waves carried by the main recirculation. Bicoherence distributions are computed to highlight the nonlinear interactions between these spanwise-travelling waves inside the cavity and the locked-on modes. The modulated envelope of the shear layer oscillations is extracted and investigated with regards to the inner-flow dynamics. Strong cross-correlations, in time rather than in space, reveal a global coupling mechanism, possibly related to the beating of the spanwise-travelling waves.
EXPERIMENTAL INVESTIGATION OF VORTEX SHEDDING FROM A PLATE - EFFECT OF EXTERNAL VELOCITY PERTURBATION
Publisher: Elsevier BV
Date: 12-1993
Application of a single-board computer as a low-cost pulse generator
Publisher: IOP Publishing
Date: 24-07-2015
Spatial evolution of the separated shear layer from a square leading-edge flat plate
Publisher: Elsevier BV
Date: 12-1993
An assessment of high-power light-emitting diodes for high frame rate schlieren imaging
Publisher: Springer Science and Business Media LLC
Date: 05-04-2012
High resolution volumetric dual-camera light-field PIV
Publisher: Springer Science and Business Media LLC
Date: 25-07-2019
Topology and dynamics of flow structures in wall-bounded turbulent flows
Publisher: IOP Publishing
Date: 22-12-2011
Measuring dynamic phenomena at the sub-micron scale
Publisher: IEEE
Date: 02-2008
BiGlobal stability analysis in curvilinear coordinates of massively separated lifting bodies
Publisher: Elsevier BV
Date: 10-2009
The effect of anomalous particle light scattering on PIV image quality
Publisher: SPIE
Date: 29-09-1998
DOI: 10.1117/12.323350
Measuring shear layer growth rates in aeroacoustically forced axisymmetric supersonic jets
Publisher: American Institute of Aeronautics and Astronautics
Date: 18-06-2015
DOI: 10.2514/6.2015-2834
Structural analysis on a hemisphere-cylinder at moderate Reynolds number and high angle of attack
Publisher: American Institute of Aeronautics and Astronautics
Date: 05-01-2013
DOI: 10.2514/6.2013-387
Direct numerical simulation of a self-similar adverse pressure gradient turbulent boundary layer at the verge of separation
Publisher: Cambridge University Press (CUP)
Date: 20-09-2017
DOI: 10.1017/JFM.2017.549
Abstract: The statistical properties are presented for the direct numerical simulation of a self-similar adverse pressure gradient (APG) turbulent boundary layer (TBL) at the verge of separation. The APG TBL has a momentum thickness-based Reynolds number range from $Re_{\\unicode[STIX]{x1D6FF}_{2}}=570$ to 13 800, with a self-similar region from $Re_{\\unicode[STIX]{x1D6FF}_{2}}=10\\,000$ to 12 300. Within this domain the average non-dimensional pressure gradient parameter $\\unicode[STIX]{x1D6FD}=39$ , where for a unit density $\\unicode[STIX]{x1D6FD}=\\unicode[STIX]{x1D6FF}_{1}P_{\\!e}^{\\prime }/\\unicode[STIX]{x1D70F}_{w}$ , with $\\unicode[STIX]{x1D6FF}_{1}$ the displacement thickness, $\\unicode[STIX]{x1D70F}_{w}$ the mean shear stress at the wall and $P_{\\!e}^{\\prime }$ the far-field pressure gradient. This flow is compared with previous zero pressure gradient and mild APG TBL ( $\\unicode[STIX]{x1D6FD}=1$ ) results of similar Reynolds number. All flows are generated via the direct numerical simulation of a TBL on a flat surface with far-field boundary conditions tailored to apply the desired pressure gradient. The conditions for self-similarity, and the appropriate length and velocity scales, are derived. The mean and Reynolds stress profiles are shown to collapse when non-dimensionalised on the basis of these length and velocity scales. As the pressure gradient increases, the extent of the wake region in the mean streamwise velocity profiles increases, whilst the extent of the log-layer and viscous sublayer decreases. The Reynolds stress, production and dissipation profiles of the APG TBL cases exhibit a second outer peak, which becomes more pronounced and more spatially localised with increasing pressure gradient. This outer peak is located at the point of inflection of the mean velocity profiles, and is suggestive of the presence of a shear flow instability. The maximum streamwise velocity variance is located at a wall normal position of $\\unicode[STIX]{x1D6FF}_{1}$ of spanwise wavelength of $2\\unicode[STIX]{x1D6FF}_{1}$ . In summary as the pressure gradient increases the flow has properties less like a zero pressure gradient TBL and more akin to a free shear layer.
Digital holography for micro-droplet diagnostics
Publisher: Springer Science and Business Media LLC
Date: 21-07-2007
An experimental investigation of coupled underexpanded supersonic twin-jets
Publisher: Springer Science and Business Media LLC
Date: 20-08-2018
On the Use of Computational Fluid Dynamics (CFD) Modelling to Design Improved Dry Powder Inhalers
Publisher: Springer Science and Business Media LLC
Date: 02-2021
A cross-correlation velocimetry technique for breakup of an annular liquid sheet
Publisher: Springer Science and Business Media LLC
Date: 13-01-2010
The visualization of the acoustic feedback loop in impinging underexpanded supersonic jet flows using ultra-high frame rate schlieren
Publisher: Springer Science and Business Media LLC
Date: 08-08-2012
Influence of ZNMF jet flow control on the spatio-temporal flow structure over a NACA-0015 airfoil
Publisher: Springer Science and Business Media LLC
Date: 28-02-2013
Stability and three-dimensional evolution of a transitional dynamic stall vortex
Publisher: Cambridge University Press (CUP)
Date: 15-06-2017
DOI: 10.1017/JFM.2017.305
Abstract: This paper describes a series of experiments using particle image velocimetry to investigate the dynamic stall resulting due to a rapid pitching motion of a flat plate. There exist in such unsteady separated flows multiple time-dependent coherent structures, whose interaction and evolution are complex and nonlinear. The experiments presented here are aimed at determining the behaviour of a dynamic stall vortex system in the Reynolds number range $10^{3} Re ^{4}$ . Evidence is presented for the development of the three-dimensional structure associated with the dynamic stall vortex and its interaction with the no-slip boundary condition at the surface of the pitching plate. The analysis presented suggests that a centrifugal instability exists, and that the form of the three-dimensional structure is consistent with that expected of a centrifugal instability. The structure and scale dependence of the flow are explored using wavelet and Fourier methods, with the dependence of the flow on Reynolds number examined, as well as the influence of spanwise end boundary conditions.
Light-field PIV Implementation and Case Studies
Publisher: Springer International Publishing
Date: 14-08-2022
Light-field Particle Image Velocimetry
Publisher: Springer International Publishing
Date: 14-08-2022
Near-field structure of underexpanded elliptic jets
Publisher: Springer Science and Business Media LLC
Date: 07-2013
Towards 3C-3D digital holographic fluid velocity vector field measurement—tomographic digital holographic PIV (Tomo-HPIV)
Publisher: IOP Publishing
Date: 23-05-2008
Influence of nozzle external geometry on wavepackets in under-expanded supersonic impinging jets
Publisher: Cambridge University Press (CUP)
Date: 27-10-2021
DOI: 10.1017/JFM.2021.822
Abstract: In this study, large-eddy simulations are utilised to unravel the influence of the nozzle's external geometry on upstream-travelling waves in under-expanded supersonic impinging jets. Three configurations, a thin-lipped, a thin-lipped with a sponge and an infinite-lipped nozzle are considered with the other non-dimensionalised geometrical and flow variables identical for the three cases. Spectral proper orthogonal decomposition is applied to the Mack norm, i.e. the energy norm based on the stagnation energy, to obtain the spatial modes at their corresponding frequency. The spectral decomposition of the spatial modes at optimal and suboptimal frequencies is used to isolate the wavepackets into upstream- and downstream-propagating waves based on their phase velocity. It is found that the external geometry of the nozzle has a significant influence on the first-order statistics even though the governing non-dimensional parameters are the same for all three cases. Multiple peaks emerge in the energy spectra at distinct frequencies corresponding to axisymmetric azimuthal modes for each case. The downstream-propagating wavepackets have a high litude at the shear layer of the three jets with the mode shapes resembling Kelvin–Helmholtz instability waves, while the upstream-travelling wavepackets exist in the three regions of the near field, shear layer and inside of the jet. The barrel shock at the nozzle exit appears as a flexible shield, which prevents upstream-travelling waves from reaching the internal region of the nozzle, where the upstream-travelling waves travel obliquely with one side of the wavefront is crawling on the reflected shock while the other side is guided by the shear layer. These latter waves can reach the nozzle lip via inside of the jet. The spectral decomposition of the spatial modes at optimal and suboptimal frequencies show that all three forms of the near field, shear layer and inside jet upstream-travelling wavepackets contribute to the receptivity process while their contributions and strength are altered by the change of the external geometry of the nozzle.
Stereoscopic PIV measurements of a turbulent boundary layer with a large spatial dynamic range
Publisher: Springer Science and Business Media LLC
Date: 08-07-2007
Using stereo multigrid DPIV (SMDPIV) measurements to investigate the vortical skeleton behind a finite-span flapping wing
Publisher: Springer Science and Business Media LLC
Date: 11-05-2005
Decomposition of Radiating and Non-Radiating Linear Fluctuating Components in Compressible Flows
Publisher: WORLD SCIENTIFIC
Date: 18-11-2015
Mean flow stability analysis of oscillating jet experiments
Publisher: Cambridge University Press (CUP)
Date: 19-09-2014
DOI: 10.1017/JFM.2014.472
Abstract: Linear stability analysis (LSA) is applied to the mean flow of an oscillating round jet with the aim of investigating the robustness and accuracy of mean flow stability wave models. The jet’s axisymmetric mode is excited at the nozzle lip through a sinusoidal modulation of the flow rate at litudes ranging from 0.1 % to 100 %. The instantaneous flow field is measured via particle image velocimetry (PIV) and decomposed into a mean and periodic part utilizing proper orthogonal decomposition (POD). Local LSA is applied to the measured mean flow adopting a weakly non-parallel flow approach. The resulting global perturbation field is carefully compared with the measurements in terms of spatial growth rate, phase velocity, and phase and litude distribution. It is shown that the stability wave model accurately predicts the excited flow oscillations during their entire growth phase and during a large part of their decay phase. The stability wave model applies over a wide range of forcing litudes, showing no pronounced sensitivity to the strength of nonlinear saturation. The upstream displacement of the neutral point and the successive reduction of gain with increasing forcing litude is very well captured by the stability wave model. At very strong forcing ( $\\def \\xmlpi #1{}\\def \\mathsfbi #1{\\boldsymbol {\\mathsf {#1}}}\\let \\le =\\leqslant \\let \\leq =\\leqslant \\let \\ge =\\geqslant \\let \\geq =\\geqslant \\def \\Pr {\\mathit {Pr}}\\def \\Fr {\\mathit {Fr}}\\def \\Rey {\\mathit {Re}}{ }40\\, \\%$ ), the flow becomes essentially stable to the axisymmetric mode. For these extreme cases, the prediction deteriorates from the measurements due to an interaction of the forced wave with the geometric confinement of the nozzle. Moreover, the model fails far downstream in a region where energy is transferred from the oscillation back to the mean flow. This study supports previously conducted mean flow stability analysis of self-excited flow oscillations in the cylinder wake and in the vortex breakdown bubble and extends the methodology to externally forced convectively unstable flows. The high accuracy of mean flow stability wave models as demonstrated here is of great importance for the analysis of coherent structures in turbulent shear flows.
Tomographic Particle Image Velocimetry Measurements of a High Reynolds Number Turbulent Boundary Layer
Publisher: Springer Netherlands
Date: 2011
Study of Vortical Structures in Turbulent Near-Wall Flows
Publisher: Springer Netherlands
Date: 2011
Estimation of Turbulent Dissipation Rate Using 2D Data in Channel Flows
Publisher: Avestia Publishing
Date: 06-2017
DOI: 10.11159/HTFF17.140
Investigation of wall-bounded turbulent flow using Dynamic mode decomposition
Publisher: IOP Publishing
Date: 22-12-2011
Stochastic self-energy subgrid model for the large eddy simulation of turbulent channel flows
Publisher: IOP Publishing
Date: 16-04-2014
Numerical issues in Lagrangian tracking and topological evolution of fluid particles in wall-bounded turbulent flows
Publisher: IOP Publishing
Date: 16-04-2014
Instability modes in screeching elliptical jets
Publisher: American Institute of Aeronautics and Astronautics
Date: 13-06-2014
DOI: 10.2514/6.2014-2891
Three-Dimensional Substructure in a Leading Edge Vortex
Publisher: American Institute of Aeronautics and Astronautics
Date: 14-06-2011
DOI: 10.2514/6.2011-3582
Signatures of shear-layer unsteadiness in proper orthogonal decomposition
Publisher: Springer Science and Business Media LLC
Date: 09-11-2018
Spectral analysis of the evolution of energy-containing eddies
Publisher: Cambridge University Press (CUP)
Date: 16-01-2023
Abstract: Energy-containing eddies (energy-eddies) are the elementary structures of wall turbulence that carry most of the kinetic energy and momentum. Despite the consensus that energy-eddies can self-sustain at each relevant length scale, their precise origin and spatial evolution are currently not well understood. In this study, we examine the spatial evolution of energy-eddies by quenching them at the inflow of a turbulent channel flow. Our study shows that the eddies involved in the energy cascade cannot be sustained without the energy-eddies. The streamwise velocity spectra of the evolving flow start to recover at a spanwise wavelength of $\\lambda _z^+ \\simeq 100$ , equal to the near-wall spacing of streaks in the buffer layer located at $y^+ \\simeq 15$ , whereas there are no active vortical motions in the streamwise vorticity spectra until the energy at the streak location is re-established. Hence, the present study demonstrates that in a spatially evolving flow, the formation of near-wall streaks is the primary process necessary in the recovery of energy-eddies.
Fluid mechanics of flapping wings
Publisher: Elsevier BV
Date: 09-2008
Investigation of large scale motions in zero and adverse pressure gradient turbulent boundary layers using high-spatial-resolution particle image velocimetry
Publisher: Elsevier BV
Date: 11-2021
Analysis of the factors contributing to the skin friction coefficient in adverse pressure gradient turbulent boundary layers and their variation with the pressure gradient
Publisher: Elsevier BV
Date: 04-2020
Ultra-high-speed 3D astigmatic particle tracking velocimetry: application to particle-laden supersonic impinging jets
Publisher: Springer Science and Business Media LLC
Date: 11-2014
Flow around a hemisphere-cylinder at high angle of attack and low Reynolds number. Part I: Experimental and numerical investigation
Publisher: Elsevier BV
Date: 07-2015
On the appropriate filtering of PIV measurements of turbulent shear flows
Publisher: Springer Science and Business Media LLC
Date: 31-12-2014
Particle image velocimetry measurements of a backward-facing step flow
Publisher: Springer Science and Business Media LLC
Date: 12-2002
Flow structures behind a heaving and pitching finite-span wing
Publisher: Cambridge University Press (CUP)
Date: 10-09-2003
Proper Orthogonal Decomposition and Dynamic Mode Decomposition of Under-Expanded Free-Jets with Varying Nozzle Pressure Ratios
Publisher: Springer International Publishing
Date: 2015
Particle image velocimetry analysis of the twin supersonic jet structure and standing-wave
Publisher: American Institute of Aeronautics and Astronautics
Date: 02-06-2017
DOI: 10.2514/6.2017-3517
Inception and evolution of coherent structures in under-expanded supersonic jets
Publisher: IOP Publishing
Date: 04-2016
A study of the fine-scale motions of incompressible time-developing mixing layers
Publisher: AIP Publishing
Date: 02-1994
DOI: 10.1063/1.868323
Abstract: The geometry of dissipating motions in direct numerical simulations (DNS) of the incompressible mixing layer is examined. All nine partial derivatives of the velocity field are determined at every grid point in the flow, and various invariants and related quantities are computed from the velocity gradient tensor. Motions characterized by high rates of kinetic energy dissipation and high enstrophy density are of particular interest. Scatter plots of the invariants are mapped out and interesting and unexpected patterns are seen. Depending on initial conditions, each type of shear layer produces its own characteristic scatter plot. In order to provide more detailed information on the distribution of invariants at intermediate and large scales, scatter plots are replaced with more useful number density contour plots. These essentially represent the unnormalized joint probability density function of the two invariants being cross-plotted. Plane mixing layers at the same Reynolds number, but with laminar and turbulent initial conditions, are studied, and comparisons of the rate-of-strain topology of the dissipating motions are made. The results show conclusively that, regardless of initial conditions, the bulk of the total kinetic energy dissipation is contributed by intermediate scale motions, whose local rate-of-strain topology is characterized as unstable-node-saddle–saddle (two positive rate-of-strain eigenvalues, one negative). In addition, it is found that, for these motions, the rate-of-strain invariants tend to approximately follow a straight line relationship, characteristic of a two-dimensional flow with out of plane straining. In contrast, fine-scale motions, which have the highest dissipation, but which only contribute a small fraction of the total dissipation tend toward a fixed ratio of the principal rates of strain.
A singularity-avoiding moving least squares scheme for two-dimensional unstructured meshes
Publisher: Elsevier BV
Date: 08-2009
Advances in soft mist inhalers
Publisher: Informa UK Limited
Date: 10-07-2023
The interaction of the piston vortex with a piston-generated vortex ring
Publisher: Cambridge University Press (CUP)
Date: 25-01-2004
An investigation of the near wake of a circular cylinder using a video-based digital cross-correlation particle image velocimetry technique
Publisher: Elsevier BV
Date: 02-1996
Heat transfer investigation on under-expanded supersonic impinging jets
Publisher: Elsevier BV
Date: 06-2023
A new perspective on spectral analysis of numerical schemes
Publisher: Wiley
Date: 12-01-2011
DOI: 10.1002/FLD.2514
A detailed comparison of single-camera light-field PIV and tomographic PIV
Publisher: Springer Science and Business Media LLC
Date: 10-02-2018
An explanation for the phase lag in supersonic jet impingement
Publisher: Cambridge University Press (CUP)
Date: 14-02-2017
DOI: 10.1017/JFM.2017.37
Abstract: For the first time, a physical mechanism is identified to explain the phase lag term in Powell’s impinging feedback loop equation (Powell, J. Acoust. Soc. Am. , vol. 83 (2), 1988, pp. 515–533). Ultra-high-speed schlieren reveals a previously unseen periodic transient shock in the wall jet region of underexpanded impinging flows. The motion of this shock appears to be responsible for the production of the acoustic waves corresponding to the impingement tone. It is suggested that the delay between the inception of the shock and the formation of the acoustic wave explains the phase lag in the aeroacoustic feedback process. This suggestion is quantitatively supported through an assessment of Powell’s feedback equation, using high-resolution particle image velocimetry and acoustic measurements.
Reynolds stress structures in a self-similar adverse pressure gradient turbulent boundary layer at the verge of separation
Publisher: IOP Publishing
Date: 04-2018
A correlation image velocimetry-based study of high-pressure fuel spray tip evolution
Publisher: Springer Science and Business Media LLC
Date: 03-04-2011
Tomographic particle image velocimetry investigation of the flow in a modeled human carotid artery bifurcation
Publisher: Springer Science and Business Media LLC
Date: 04-02-2011
Characterisation of minimal-span plane Couette turbulence with pressure gradients
Publisher: IOP Publishing
Date: 04-2018
Intermittent modal coupling in screeching underexpanded circular twin jets
Publisher: Cambridge University Press (CUP)
Date: 11-01-2021
DOI: 10.1017/JFM.2020.909
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
Pulsed, high-power LED illumination for tomographic particle image velocimetry
Publisher: Springer Science and Business Media LLC
Date: 10-10-2012
On the behaviour of impinging zero-net-mass-flux jets
Publisher: Cambridge University Press (CUP)
Date: 24-11-2016
DOI: 10.1017/JFM.2016.703
Abstract: This paper reports on an experimental study of the influence of the Strouhal number (0.011, 0.022 and 0.044) and orifice-to-plate distances (2, 4 and 6 orifice diameters) on the flow field of an impinging zero-net-mass-flux jet at a Reynolds number equal to 35 000. These jets are generated by a reciprocating piston that oscillates in a cavity behind a circular orifice. Instantaneous two-dimensional in-plane velocity fields are measured in a plane containing the orifice axis using multigrid/multipass cross-correlation digital particle image velocimetry. These measurements have been used to investigate the mean flow quantities and turbulent statistics of the impinging zero-net-mass-flux jets. In addition, the vortex ring behaviour is analysed via its trajectory and azimuthal vorticity as well as the saddle point excursion, the flow rate and entrainment. The behaviour of all these quantities depends on the Strouhal number and the orifice-to-plate distance because the former governs the presence and the relative importance of the vortex ring and the trailing jet on the flow field and the latter delimits the downstream evolution of these structures.
Boundary Condition Development for an Adverse Pressure Gradient Turbulent Boundary Layer at the Verge of Separation
Publisher: WORLD SCIENTIFIC
Date: 18-11-2015
An efficient simultaneous reconstruction technique for tomographic particle image velocimetry
Publisher: Springer Science and Business Media LLC
Date: 27-08-2009
Shear layer vortices and longitudinal vortices in the near wake of a circular cylinder
Publisher: Elsevier BV
Date: 02-1996
Analysis of a drag reduced flat plate turbulent boundary layer via uniform momentum zones
Publisher: Elsevier BV
Date: 2020
Linearised dynamics and non-modal instability analysis of an impinging under-expanded supersonic jet
Publisher: IOP Publishing
Date: 04-2018
Stereoscopic and tomographic PIV of a pitching plate
Publisher: Springer Science and Business Media LLC
Date: 11-2012
Towards the Direct Numerical Simulation of a Self-similar Adverse Pressure Gradient Turbulent Boundary Layer Flow
Publisher: Springer International Publishing
Date: 31-08-2016
Volume integrals of theQA-RAinvariants of the velocity gradient tensor in incompressible flows
Publisher: IOP Publishing
Date: 04-1997
Upstream-travelling acoustic jet modes as a closure mechanism for screech
Publisher: Cambridge University Press (CUP)
Date: 20-09-2018
DOI: 10.1017/JFM.2018.642
Abstract: Experimental evidence is provided to demonstrate that the upstream-travelling waves in two jets screeching in the A1 and A2 modes are not free-stream acoustic waves, but rather waves with support within the jet. Proper orthogonal decomposition is used to educe the coherent fluctuations associated with jet screech from a set of randomly s led velocity fields. A streamwise Fourier transform is then used to isolate components with positive and negative phase speeds. The component with negative phase speed is shown, by comparison with a vortex-sheet model, to resemble the upstream-travelling jet wave first studied by Tam & Hu ( J. Fluid Mech. , vol. 201, 1989, pp. 447–483). It is further demonstrated that screech tones are only observed over the frequency range where this upstream-travelling wave is propagative.
The underexpanded jet Mach disk and its associated shear layer
Publisher: AIP Publishing
Date: 09-2014
DOI: 10.1063/1.4894741
Abstract: High resolution planar particle image velocimetry is used to measure turbulent quantities in the region downstream of the Mach disk in an axisymmetric underexpanded jet issuing from a convergent nozzle. The internal annular shear layer generated by the slip line emanating from the triple point is shown to persist across multiple shock cells downstream. A triple decomposition based on Proper Orthogonal Decomposition shows that the external helical structure associated with the screech tone generated by the jet exerts a strong influence on velocity fluctuations in the initial region of the annular shear layer. This influence manifests as the external vortices producing oscillatory motion of the Mach disk, and thus a forcing of the internal annular shear layer. The internal shear layer is characterized by a number of azimuthal modes of varying wavenumber and type, including both helical and axisymmetric modes. Finally, the possibility of a previously hypothesized recirculation region behind the Mach disk is investigated, with no evidence found to support its existence.
Scale and Reynolds number dependence of stochastic subgrid energy transfer in turbulent channel flow
Publisher: Elsevier BV
Date: 06-2017
The evolution of round zero-net-mass-flux jets
Publisher: Cambridge University Press (CUP)
Date: 30-11-2002
DOI: 10.1017/S0022112002002264
Abstract: This paper reports on an experimental investigation to determine the structure and mean flow quantities of round zero-net-mass-flux (ZNMF) jets. These jets are generated by a piston oscillating in a cavity behind a circular orifice. Several different flow patterns were observed with dye flow visualization and a parameter map of these was generated. Cross-correlation digital particle image velocimetry was used to measure instantaneous two-dimensional in-plane velocity fields in a plane containing the orifice axis. These velocity fields are used to investigate the existence of a self-preserving velocity profile in the far field of the ZNMF jet. The mean flow quantities and turbulent statistics of the ZNMF jets were compared with measurements for ‘equivalent’ continuous jets in the same apparatus. Phase-averaged velocity measurements were obtained in the near field of the ZNMF jets and were used to determine the radial entrainment. The out-of-plane vorticity fields were also investigated to gain an understanding of the mechanisms responsible for the difference in spreading rate of ZNMF jets compared to conventional continuous jets. A conceptual model of the ZNMF jet structure in the near field for Strouhal numbers much less than one is proposed that explains the observed behaviour of these ZNMF jets.
Prologue to the International Conference on Massively Separated Flows and Their Control
Publisher: Springer International Publishing
Date: 2015
Recovery of the Koopman modes of a Leading-Edge separated aerofoil flow via a proper orthogonal decomposition rank reduction
Publisher: Springer International Publishing
Date: 2015
Effect of nozzle transients and compressibility on the penetration of fuel sprays
Publisher: AIP Publishing
Date: 13-07-2009
DOI: 10.1063/1.3182821
Abstract: A study has been performed using a combination of high speed optical imaging and a synchrotron based technique to obtain a time history of nozzle exit velocity, discharge coefficient, and spray tip velocity of high pressure fuel sprays. The results support a recently proposed theoretical model of spray propagation that suggests a compressible region of flow immediately ahead of the spray has a strong influence on the evolution of the tip velocity profile. Coupled with this is the variation in discharge coefficient due to injector needle movement which largely governs the spray exit velocity immediately after start of injection.
Investigation of coherent structures and dynamics using POD and DMD of a separated airfoil subjected to ZNMF jet forcing
Publisher: Springer International Publishing
Date: 2015
Investigation of the mean passive scalar field in zero-net-mass-flux jets in cross-flow using planar-laser-induced fluorescence
Publisher: AIP Publishing
Date: 04-02-2004
DOI: 10.1063/1.1647143
Abstract: Planar-laser-induced fluorescence (PLIF) measurements have been used to investigate the mean passive scalar field in round zero-net-mass-flux jets in cross-flow (ZNMF-JICF). The ZNMF-JICF are formed in a working fluid without net transfer of mass across the system boundary during one period of oscillation. Ensemble-averaged PLIF images of sixteen different ZNMF-JICF are studied and compared. Two distinct flow regimes are observed single trajectory ZNMF-JICF and multiple trajectory ZNMF-JICF. Single trajectory ZNMF-JICF demonstrate mixing of the bulk of the fluid outside the upstream boundary layer, while multiple trajectory ZNMF-JICF can penetrate more deeply into the ambient cross-flow. A critical Strouhal number of Stcrit=0.02 was found for the generation apparatus that can be used to distinguish between these two regimes. The penetration of the single trajectory ZNMF-JICF does not exhibit the same dependence on velocity ratio observed in the measurements of continuous JICF.
Characterisation of uniform momentum zones in adverse pressure gradient turbulent boundary layers
Publisher: Elsevier BV
Date: 07-2020
High-order accurate large-eddy simulations of compressible viscous flow in cylindrical coordinates
Publisher: Elsevier BV
Date: 09-2019
Multigrid CCDPIV measurements of accelerated flow past an airfoil at an angle of attack of 30°
Publisher: Elsevier BV
Date: 05-2003
Supersonic jet impingement on a cylindrical surface
Publisher: American Institute of Aeronautics and Astronautics
Date: 27-05-2016
DOI: 10.2514/6.2016-2800
A novel method for decoupling the velocity fluctuations in screeching axisymmetric jets
Publisher: American Institute of Aeronautics and Astronautics
Date: 27-05-2016
DOI: 10.2514/6.2016-2801
Three-Dimensional Waves Inside an Open Cavity and Interactions with the Impinging Shear Layer
Publisher: Springer International Publishing
Date: 2015
The growth of instabilities in annular liquid sheets
Publisher: Elsevier BV
Date: 11-2015
A film-based wall shear stress sensor for wall-bounded turbulent flows
Publisher: Springer Science and Business Media LLC
Date: 09-01-2011
The relationship between the topological structures in turbulent flow and the distribution of a passive scalar with an imposed mean gradient
Publisher: IOP Publishing
Date: 03-2005
Near and far field laminar flow structures in an axisymmetric zero-net-mass-flux jet
Publisher: Elsevier BV
Date: 10-2020
Near-field pairing of leading-edge vortices in elliptic jets in cross flow
Publisher: Elsevier BV
Date: 05-2004
PIV measurements of a zero-net-mass-flux jet in cross flow
Publisher: Springer Science and Business Media LLC
Date: 12-2002
Proposed stochastic parameterisations of subgrid turbulence in large eddy simulations of turbulent channel flow
Publisher: Informa UK Limited
Date: 08-04-2015
A comparison of subpixel edge detection and correlation algorithms for the measurement of sprays
Publisher: SAGE Publications
Date: 06-2011
Abstract: Optical diagnostic techniques are commonly used to observe the breakup of dense sprays. In order to extract quantitative data from such images, edge detection algorithms have commonly been used. However, correlation image velocimetry techniques are now also becoming available for such applications. An empirical comparison between these two techniques is demonstrated for the high-speed velocimetry of the breakup of an annular air-assisted spray. A threshold based sub-pixel interpolating edge detection algorithm is employed. Both real and synthetic images are used to determine the sensitivity of the error in these techniques to changes in both image noise and defocus, the two leading causes of information loss. It is demonstrated that correlation image velocimetry techniques are generally superior in precision and accuracy as compared to edge detection techniques for the application of spray velocimetry within a reasonable parameter space of noise and defocus.
Measurements of the flow due to a rapidly pitching plate using time resolved high resolution PIV
Publisher: Elsevier BV
Date: 07-2015
Linear modelling of self-similar jet turbulence
Publisher: Cambridge University Press (CUP)
Date: 25-05-2021
DOI: 10.1017/JFM.2021.292
Impingement tones and associated shock instabilities in supersonic plug nozzle flows
Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 09-2016
DOI: 10.2514/1.J054429
Experimental Studies of the Near-Field Spatio-Temporal Evolution of Zero-Net-Mass-Flux (ZNMF) Jets
Publisher: Springer Singapore
Date: 2015
Behavior of an elastic fluid in cylindrical swirling flow
Publisher: Elsevier BV
Date: 02-1996
Insights into Spray Development from Metered-Dose Inhalers Through Quantitative X-ray Radiography
Publisher: Springer Science and Business Media LLC
Date: 17-02-2016
DOI: 10.1007/S11095-016-1869-5
Abstract: Typical methods to study pMDI sprays employ particle sizing or visible light diagnostics, which suffer in regions of high spray density. X-ray techniques can be applied to pharmaceutical sprays to obtain information unattainable by conventional particle sizing and light-based techniques. We present a technique for obtaining quantitative measurements of spray density in pMDI sprays. A monochromatic focused X-ray beam was used to perform quantitative radiography measurements in the near-nozzle region and plume of HFA-propelled sprays. Measurements were obtained with a temporal resolution of 0.184 ms and spatial resolution of 5 μm. Steady flow conditions were reached after around 30 ms for the formulations examined with the spray device used. Spray evolution was affected by the inclusion of ethanol in the formulation and unaffected by the inclusion of 0.1% drug by weight. Estimation of the nozzle exit density showed that vapour is likely to dominate the flow leaving the inhaler nozzle during steady flow. Quantitative measurements in pMDI sprays allow the determination of nozzle exit conditions that are difficult to obtain experimentally by other means. Measurements of these nozzle exit conditions can improve understanding of the atomization mechanisms responsible for pMDI spray droplet and particle formation.
On measuring the joint probability density function of three-dimensional velocity components in turbulent flows
Publisher: IOP Publishing
Date: 23-04-2012
Measurements of a wall-bounded, turbulent, separated flow using HPIV
Publisher: Informa UK Limited
Date: 2001
Direct numerical simulations of vortex breakdown in swirling jets
Publisher: Informa UK Limited
Date: 2001
Experimental investigation of nonlinear instabilities in annular liquid sheets
Publisher: Cambridge University Press (CUP)
Date: 10-01-2012
DOI: 10.1017/JFM.2011.516
Abstract: The aerodynamically driven annular liquid sheet exhibits a complex nonlinear instability. Novel interfacial velocimetry experiments suggest that two distinct physical sources of instability may be present. The first is the well-known free shear layer instability, which is quasi-sinusoidal and nonlinear. The second is a distinct nonlinear rupturing instability, modulated on the previous one. It may be directly driving primary atomization. This instability has not been previously observed in isolation and is inherently nonlinear and non-sinusoidal. Novel application of Koopman analysis and the Hilbert transform permit investigation of these distinct instabilities. A greater understanding of the rupturing instability may lead to a better understanding of atomization phenomena.
Separation control on a NACA 0015 airfoil using a 2D micro ZNMF jet
Publisher: Emerald
Date: 21-03-2008
DOI: 10.1108/00022660810859391
Abstract: The aims of this study were to investigate the effect of using a wall‐normal, 2D micro zero‐net‐mass‐flux (ZNMF) jet located at the leading edge of a NACA 0015 airfoil to actively control flow separation and enhance lift. Experiments were conducted over a two‐dimensional airfoil in a water tunnel at a Reynolds number of 3.08 × 10 4 for the parametric investigation and the detailed multigrid cross‐correlation digital particle image velocimetry (MCCDPIV) measurements. Flow visualisation experiments were carried out at a lower Reynolds number of 1.54 × 10 4 . The largest lift increase was observed when a non‐dimensional frequency of 1.3 and an oscillatory momentum blowing coefficient of 0.14 per cent was employed. Under these forcing conditions the stall angle of the airfoil was mitigated from an angle of attack of 10 o to one of 18 o , resulting in a maximum lift coefficient increase of 46 per cent above the uncontrolled lift coefficient. Planar laser induced fluoroscopy and MCCDPIV revealed that the lift increments were the result of the generation of a train of large‐scale, spanwise lifting vortices that convected over the suction surface of the airfoil. The presence of these structures resulted in the flow seemingly remaining attached to the upper surface of the airfoil for a wider range of angles of attack. This study is significant as it provides quantitative experimental data, which clearly demonstrates the effectiveness of a 2D micro ZNMF jet in controlling flow separation of a NACA 0015 airfoil at high angles of attack and thus, enhancing lift. Furthermore, the flow visualisations and MCCDPIV measurements have provided insight into the mechanisms responsible for the improvement in lift. This new understanding has applications beyond the NACA 0015 airfoil used in this study.
Scale dependent stochastic self-energy model of the energy transfers in turbulent channel flows
Publisher: Springer International Publishing
Date: 2016
On the effects of nozzle lip thickness on the azimuthal mode selection of a supersonic impinging flow
Publisher: American Institute of Aeronautics and Astronautics
Date: 02-06-2017
DOI: 10.2514/6.2017-3031
Influence of Eddy Viscosity on Linear Modeling of Self-Similar Coherent Structures in the Jet Far Field
Publisher: American Institute of Aeronautics and Astronautics
Date: 03-01-2022
DOI: 10.2514/6.2022-0460
Thrust Measurements from a Finite-Span Flapping Wing
Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 2007
DOI: 10.2514/1.18217
Time resolved measurements of the initial stages of fuel spray penetration
Publisher: Elsevier BV
Date: 11-2009
Investigating the Linear Dynamics of the Near-Field of a Turbulent High-Speed Jet Using Dual-Particle Image Velocimetry (PIV) and Dynamic Mode Decomposition (DMD)
Publisher: MDPI AG
Date: 17-02-2023
Abstract: The quest for the physical mechanisms underlying turbulent high-speed jet flows is underpinned by the extraction of spatio-temporal coherent structures from their flow fields. Experimental measurements to enable data decomposition need to comprise time-resolved velocity fields with a high-spatial resolution—qualities which current particle image velocimetry hardware are incapable of providing. This paper demonstrates a novel approach that addresses this challenge through the implementation of an experimental high-spatial resolution dual-particle image velocimetry methodology coupled with dynamic mode decomposition. This new approach is exemplified by its application in studying the dynamics of the near-field region of a turbulent high-speed jet, enabling the spatio-temporal structure to be investigated by the identification of the spatial structure of the dominant dynamic modes and their temporal dynamics. The spatial lification of these modes is compared with that predicted by classical linear stability theory, showing close agreement, which demonstrates the powerful capability of this technique to identify the dominant frequencies and their associated spatial structures in high-speed turbulent flows.
Lagrangian evolution of the invariants of the velocity gradient tensor in a turbulent boundary layer
Publisher: AIP Publishing
Date: 10-2012
DOI: 10.1063/1.4757656
Abstract: Lagrangian mean evolution of the invariants of the velocity gradient tensor in different regions of a turbulent boundary layer is investigated using data from a direct numerical simulation of a zero pressure gradient turbulent boundary layer. Conditional mean trajectories (CMTs) are calculated for the evolution of invariants based on their mean rate of change, conditioned on their location in the (RA, QA) plane, which determines the focal or non-focal nature of flow at that point. CMTs are calculated over a larger range of gradients than previously reported boundary layer measurements and show a distinct difference in topological evolution depending on the resolution and the range of invariants considered. In the present case, CMTs for strong gradients in all regions of the boundary layer pass around a focus at the origin and asymptote towards the right-hand side of a saddle point located near the right-hand side of the line iding unstable focal and unstable nodal structures, consistent with viscous diffusion dominated evolution. Closer to the origin, weaker gradients follow an almost periodic clockwise spiraling evolution from stable-focus stretching to unstable-focus contraction, unstable-node saddle/saddle, and stable-node saddle/saddle topology, similar to that observed in homogeneous isotropic turbulence. Mean time-scales associated with the spiraling evolution in terms of inner scales are estimated at 67.9 \\documentclass[12pt]{minimal}\\begin{document}$\\nu /u^2_\\tau$\\end{document}ν/uτ2 in the viscous layer, 151 \\documentclass[12pt]{minimal}\\begin{document}$\\nu /u^2_\\tau$\\end{document}ν/uτ2 in the buffer layer, and 658 \\documentclass[12pt]{minimal}\\begin{document}$\\nu /u^2_\\tau$\\end{document}ν/uτ2 in the log and wake region. Iso-contours of coherent vortices indicate that these structures typically involve stronger gradients beyond that of the spiraling evolution.
Coherent structure and sound production in the helical mode of a screeching axisymmetric jet
Publisher: Cambridge University Press (CUP)
Date: 08-05-2014
DOI: 10.1017/JFM.2014.173
Abstract: The structure of a screeching axisymmetric jet in the helical C mode at a nozzle pressure ratio of 3.4 issuing from a convergent nozzle is studied using high-resolution particle image velocimetry. Proper orthogonal decomposition (POD) is used to extract the dominant coherent structures within the jet. The first two modes produced by the POD are used to reconstruct a phase-averaged data sequence. A triple decomposition into mean, coherent and random velocity components is performed. The embedded shock structures within the jet are shown to strongly modulate the coherent axial stresses within the shear layer and to weakly modulate the random axial stresses. Analysis of the third and fourth moments of the velocity probability density function is used as an indicator of possible regions of shock–vortex interaction and thus screech tone generation. Peaks of kurtosis (flatness) occur at the second, third and fourth shock–boundary intersection points, with the radial position shifting towards the centreline with increasing downstream distance. Analysis of the coherent component of vorticity shows that the largest fluctuations in coherent vorticity occur at the high-speed side of the shear layer in an area extending from the second to the fourth shock cell. With reference to prior literature, the argument is made that it is this increased magnitude of coherent vorticity fluctuation that is the primary factor in the determination of which shock cells act as dominant screech sources.
Near-wall statistics of a turbulent pipe flow at shear Reynolds numbers up to 40 000
Publisher: Cambridge University Press (CUP)
Date: 15-08-2017
DOI: 10.1017/JFM.2017.498
Abstract: This paper reports on near-wall two-component–two-dimensional (2C–2D) particle image velocimetry (PIV) measurements of a turbulent pipe flow at shear Reynolds numbers up to $Re_{\\unicode[STIX]{x1D70F}}=40\\,000$ acquired in the CICLoPE facility of the University of Bologna. The 111.5 m long pipe of 900 mm diameter offers a well-established turbulent flow with viscous length scales ranging from $85~\\unicode[STIX]{x03BC}\\text{m}$ at $Re_{\\unicode[STIX]{x1D70F}}=5000$ down to $11~\\unicode[STIX]{x03BC}\\text{m}$ at $Re_{\\unicode[STIX]{x1D70F}}=40\\,000$ . These length scales can be resolved with a high-speed PIV camera at image magnification near unity. Statistically converged velocity profiles were determined using multiple sequences of up to 70 000 PIV recordings acquired at s ling rates of 100 Hz up to 10 kHz. Analysis of the velocity statistics shows a well-resolved inner peak of the streamwise velocity fluctuations that grows with increasing Reynolds number and an outer peak that develops and moves away from the inner peak with increasing Reynolds number.
High resolution multigrid cross-correlation digital PIV measurements of a turbulent starting jet using half frame image shift film recording
Publisher: Elsevier BV
Date: 02-1999
On the mechanism of elasto-inertial turbulence
Publisher: AIP Publishing
Date: 17-09-2013
DOI: 10.1063/1.4820142
Abstract: Elasto-inertial turbulence (EIT) is a new state of turbulence found in inertial flows with polymer additives. The dynamics of turbulence generated and controlled by such additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 (based on the bulk and the channel height) are used to study the formation and dynamics of elastic instabilities and their effects on the flow. The flow topology of EIT is found to differ significantly from Newtonian wall-turbulence. Structures identified by positive (rotational flow topology) and negative (extensional/compressional flow topology) second invariant Qa isosurfaces of the velocity gradient are cylindrical and aligned in the spanwise direction. Polymers are significantly stretched in sheet-like regions that extend in the streamwise direction with a small upward tilt. The Qa cylindrical structures emerge from the sheets of high polymer extension, in a mechanism of energy transfer from the fluctuations of the polymer stress work to the turbulent kinetic energy. At subcritical Reynolds numbers, EIT is observed at modest Weissenberg number (Wi, ratio polymer relaxation time to viscous time scale). For supercritical Reynolds numbers, flows approach EIT at large Wi. EIT provides new insights on the nature of the asymptotic state of polymer drag reduction (maximum drag reduction), and explains the phenomenon of early turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian flows observed in some polymeric flows.
Formation of Three-Dimensional Structures in the Hemisphere-Cylinder
Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 12-2016
DOI: 10.2514/1.J055011
Morphology of the forced oscillatory flow past a finite-span wing at low Reynolds number
Publisher: Cambridge University Press (CUP)
Date: 04-01-2007
DOI: 10.1017/S0022112006003491
Abstract: A study of the morphology of the vortical skeleton behind a flapping NACA0030 wing with a finite aspect ratio of 3, is undertaken. The motivation for this work originates with the proposal that thrust can be efficiently produced by flapping aerofoils. The test condition corresponds to a Strouhal number of 0.35, Reynolds number, based on aerofoil chord, of 600 and an litude of flapping, equal to the chord length of the wing. This test condition corresponds to the optimal thrust-producing case in infinite-span flapping wings. This study investigates the effect of wing three-dimensionality on the structure of the wake-flow. This is accomplished here, by quantitatively describing the spatio-temporal variations in the velocity, vorticity and Reynolds stresses for the finite-span-wing case. Preliminary flow visualizations suggest that the presence of wingtip vortices for the three-dimensional-wing case, create a different vortical structure to the two-dimensional-wing case. In the case of a two-dimensional-wing, the flow is characterized by the interaction of leading- and trailing-edge vorticity, resulting in the formation of a clear reverse Kármán vortex street at the selected test condition. In the case of a three-dimensional-wing, the flow exhibits a high degree of complexity and three-dimensionality, particularly in the midspan region. Using phase-averaged particle image velocimetry measurements of the forced oscillatory flow, a quantitative analysis in the plane of symmetry of the flapping aerofoil was undertaken. Using a triple decomposition of the measured velocities, the morphological characteristics of the spanwise vorticity is found to be phase correlated with the aerofoil kinematics. Reynolds stresses in the direction of oscillation are the dominant dissipative mechanism. The mean velocity profiles resemble a jet , indicative of thrust production. Pairs of strong counter-rotating vortices from the leading- and trailing-edge of the aerofoil are shed into the flow at each half-cycle. The large-scale structure of the flow is characterized by constructive merging of spanwise vorticity. The midspan region is populated by cross-sections of interconnected vortex rings.
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.
The generation of screech tones by shock leakage
Publisher: Cambridge University Press (CUP)
Date: 15-12-2021
DOI: 10.1017/JFM.2020.945
The size dependant behaviour of particles driven by a travelling surface acoustic wave (TSAW)
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8LC01155A
Abstract: Travelling surface acoustic waves (TSAW) can cause particles to follow the swirling patterns of acoustic streaming, collect in lines or migrate away from the sound source, this paper examines how particle size determines which one of these behaviours occur.
Use of zero-net-mass-flow for separation control in diffusing S-duct
Publisher: Elsevier BV
Date: 10-2008
Assessment of three-dimensional density measurements from tomographic background-oriented schlieren (BOS)
Publisher: IOP Publishing
Date: 10-09-2020
The effect of transverse plate vibration on the mean laminar convective boundary layer heat transfer rate
Publisher: Elsevier BV
Date: 03-1991
An error analysis of the dynamic mode decomposition
Publisher: Springer Science and Business Media LLC
Date: 03-12-2012
The structure and dynamics of backflow in turbulent channels
Publisher: Cambridge University Press (CUP)
Date: 07-10-2019
DOI: 10.1017/JFM.2019.774
Abstract: A statistical description of flow regions with negative streamwise velocity is provided based on simulations of turbulent plane channels in the Reynolds number range $547\\leqslant Re_{\\unicode[STIX]{x1D70F}}\\leqslant 2003$ . It is found that regions of backflow are attached and their density per surface area – in wall units – is an increasing function of $Re_{\\unicode[STIX]{x1D70F}}$ . Their size distribution along the three coordinates reveals that, even though in the mean they appear to be circular in the wall-parallel plane, they tend to become more elongated in the spanwise direction after reaching a certain height. Time-tracking of backflow regions in a $Re_{\\unicode[STIX]{x1D70F}}=934$ simulation showed they convect downstream at the mean velocity corresponding to $y^{+}\\approx 12$ , they seldom interact with other backflow events, their statistical signature extends in the streamwise direction for at least $300$ wall units, and they result from a complex interaction between regions of high and low spanwise vorticity far beyond the viscous sublayer. This could explain why some statistical aspects of these near-wall events do not scale in viscous units they are dependent on the $Re_{\\unicode[STIX]{x1D70F}}$ -dependent dynamics further away from the wall.
Scaling and statistics of large-defect adverse pressure gradient turbulent boundary layers
Publisher: Elsevier BV
Date: 06-2016
A comparison between snapshot POD analysis of PIV velocity and vorticity data
Publisher: Springer Science and Business Media LLC
Date: 12-01-2005
A Numerical Investigation of the Cold Spray Process Using Underexpanded and Overexpanded Jets
Publisher: Springer Science and Business Media LLC
Date: 18-10-2011
Simulation and characterization of the laminar separation bubble over a NACA-0012 airfoil as a function of angle of attack
Publisher: American Physical Society (APS)
Date: 02-03-2021
A novel high-speed imaging technique to predict the macroscopic spray characteristics of solution based pressurised metered dose inhalers
Publisher: Springer Science and Business Media LLC
Date: 17-06-2014
DOI: 10.1007/S11095-014-1391-6
Abstract: Non-volatile agents such as glycerol are being introduced into solution-based pMDI formulations in order to control mean precipitant droplet size. To assess their biopharmaceutical efficacy, both microscopic and macroscopic characteristics of the plume must be known, including the effects of external factors such as the flow generated by the patient's inhalation. We test the hypothesis that the macroscopic properties (e.g. spray geometry) of a pMDI spray can be predicted using a self-similarity model, avoiding the need for repeated testing. Glycerol-containing and glycerol-free pMDI formulations with matched mass median aerodynamic diameters are investigated. High-speed schlieren imaging is used to extract time-resolved velocity, penetration and spreading angle measurements of the pMDI spray plume. The experimental data are used to validate the analytical model. The pMDI spray develops in a manner characteristic of a fully-developed steady turbulent jet, supporting the hypothesis. Equivalent glycerol-containing and non glycerol-containing formulations exhibit similar non-dimensional growth rates and follow a self-similar scaling behaviour over a range of physiologically relevant co-flow rates. Using the proposed model, the mean leading edge penetration, velocity and spreading rate of a pMDI spray may be estimated a priori for any co-flow conditions. The effects of different formulations are captured in two scaling constants. This allows formulators to predict the effects of variation between pMDIs without the need for repeated testing. Ultimately, this approach will allow pharmaceutical scientists to rapidly test a number of variables during pMDI development.
On the identification of intense Reynolds stress structures in wall-bounded flows using information-limited two-dimensional planar data
Publisher: Elsevier BV
Date: 2016
Time-resolved stereo PIV measurements in the far-field of a turbulent zero-net-mass-flux jet
Publisher: Elsevier BV
Date: 09-2014
On the role of pressure in elasto-inertial turbulence
Publisher: Informa UK Limited
Date: 02-09-2014
Ultra-high-speed tomographic digital holographic velocimetry in supersonic particle-laden jet flows
Publisher: IOP Publishing
Date: 20-12-2013
Novel method for investigating broadband velocity fluctuations in axisymmetric screeching jets
Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 07-2017
DOI: 10.2514/1.J055606
Experiments in Fluids
Publisher: Springer Science and Business Media LLC
Date: 29-08-2011
An experimental investigation of streamwise vortices in the wake of a bluff body
Publisher: Elsevier BV
Date: 1994
Accelerated flow past a symmetric aerofoil: experiments and computations
Publisher: Cambridge University Press (CUP)
Date: 30-10-2007
DOI: 10.1017/S0022112007008464
Abstract: Accelerated flow past a NACA 0015 aerofoil is investigated experimentally and computationally for Reynolds number Re = 7968 at an angle of attack α = 30°. Experiments are conducted in a specially designed piston-driven water tunnel capable of producing free-stream velocity with different r -type accelerations, and the DPIV technique is used to measure the resulting flow field past the aerofoil. Computations are also performed for other published data on flow past an NACA 0015 aerofoil in the range 5200 ≤ Re ≤ 35000, at different angles of attack. One of the motivations is to see if the salient features of the flow captured experimentally can be reproduced numerically. These computations to solve the incompressible Navier–Stokes equation are performed using high-accuracy compact schemes. Load and moment coefficient variations with time are obtained by solving the Poisson equation for the total pressure in the flow field. Results have also been analysed using the proper orthogonal decomposition technique to understand better the evolving vorticity field and its dependence on Reynolds number and angle of attack. An energy-based stability analysis is performed to understand unsteady flow separation.
Pre-detachment Acoustic Emission of a Bubble Emerging from an Orifice
Publisher: Springer Berlin Heidelberg
Date: 18-12-2015
Characteristics of acoustic and hydrodynamic waves in under-expanded supersonic impinging jets
Publisher: Cambridge University Press (CUP)
Date: 04-11-2020
DOI: 10.1017/JFM.2020.740
In-vitro and particle image velocimetry studies of dry powder inhalers
Publisher: Elsevier BV
Date: 2021
Sound production by shock leakage in supersonic jet screech
Publisher: American Institute of Aeronautics and Astronautics
Date: 24-06-2018
DOI: 10.2514/6.2018-3147
Combining experimental and computational techniques to understand and improve dry powder inhalers
Publisher: Informa UK Limited
Date: 02-01-2022
DOI: 10.1080/17425247.2022.2026922
Abstract: Dry Powder Inhalers (DPIs) continue to be developed to deliver an expanding range of drugs to treat an ever-increasing range of medical conditions with each drug and device combination needing a specifically designed inhaler. Fast regulatory approval is essential to be first to market, ensuring commercial profitability. Experimental techniques and computational methods are improving rapidly, but each needs a skilled user to maximize results obtained from these techniques. Multidisciplinary teams are therefore key to making optimal use of these methods and such qualified teams can provide enormous benefits to pharmaceutical companies to improve device efficacy and thus time to market. There is already a move to integrate the benefits of Industry 4.0 into inhaler design and usage, a trend that will accelerate.
An experimental investigation of turbulent convection velocities in a turbulent boundary layer
Publisher: Springer Science and Business Media LLC
Date: 20-12-2015
Flagellar energetics from high-resolution imaging of beating patterns in tethered mouse sperm
Publisher: eLife Sciences Publications, Ltd
Date: 30-04-2021
DOI: 10.7554/ELIFE.62524
Abstract: We demonstrate a technique for investigating the energetics of flagella or cilia. We record the planar beating of tethered mouse sperm at high resolution. Beating waveforms are reconstructed using proper orthogonal decomposition of the centerline tangent-angle profiles. Energy conservation is employed to obtain the mechanical power exerted by the dynein motors from the observed kinematics. A large proportion of the mechanical power exerted by the dynein motors is dissipated internally by the motors themselves. There could also be significant dissipation within the passive structures of the flagellum. The total internal dissipation is considerably greater than the hydrodynamic dissipation in the aqueous medium outside. The net power input from the dynein motors in sperm from Crisp2 -knockout mice is significantly smaller than in wildtype s les, indicating that ion-channel regulation by cysteine-rich secretory proteins controls energy flows powering the axoneme.
Time-resolved Particle Image Velocimetry and Structural Analysis on An Hemisphere-Cylinder at Low Reynolds Numbers and Large Angle of Incidence
Publisher: American Institute of Aeronautics and Astronautics
Date: 25-06-2012
DOI: 10.2514/6.2012-3275
Local topology via the invariants of the velocity gradient tensor within vortex clusters and intense Reynolds stress structures in turbulent channel flow
Publisher: IOP Publishing
Date: 04-2016
Nozzle external geometry as a boundary condition for the azimuthal mode selection in an impinging underexpanded jet
Publisher: Cambridge University Press (CUP)
Date: 11-01-2019
DOI: 10.1017/JFM.2018.957
Abstract: The role of the external boundary conditions of the nozzle surface on the azimuthal mode selection of impinging supersonic jets is demonstrated for the first time. Jets emanating from thin- and infinite-lipped nozzles at a nozzle pressure ratio of $3.4$ and plate spacing of $5.0D$ , where $D$ is the nozzle exit diameter, are investigated using high resolution particle image velocimetry (PIV) and acoustic measurements. Proper orthogonal decomposition is applied to the PIV fields and a difference in dominant instability mode is found. To investigate possible explanations for the change in instability mode, additional nozzle external boundary conditions are investigated, including the addition of acoustic d ening foam. A difference in acoustic feedback path is suggested to be the cause for the change in dominant azimuthal modes between the flows. This is due to the thin-lip case containing a feedback path that is concluded to be closed exclusively by a reflection from the nozzle base surface, rather than directly to the nozzle lip. The ability of the flow to form a feedback path that maximises the impingement tone gain is discussed with consideration of the numerous acoustic feedback paths possible for the given nozzle external boundary conditions.
Comparison of the Direct Numerical Simulation of Zero and Low Adverse Pressure Gradient Turbulent Boundary Layers
Publisher: Springer Berlin Heidelberg
Date: 18-12-2015
Editorial: PIV’09 special issue
Publisher: Springer Science and Business Media LLC
Date: 13-03-2011
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