Papers by Jose E . Wesfreid
Physical review fluids, Jan 23, 2018
The wake behind a sphere, rotating about an axis aligned with the streamwise direction, has been ... more The wake behind a sphere, rotating about an axis aligned with the streamwise direction, has been experimentally investigated in a low-velocity water tunnel using LIF visualizations and PIV measurements. The measurements focused on the evolution of the flow regimes that appear depending on two control parameters, namely the Reynolds number Re and the dimensionless rotation or swirl rate Ω, which is the ratio of the maximum azimuthal velocity of the body to the free stream velocity. In the present investigation, we cover the range of Re smaller than 400 and Ω from 0 and 4. Different wakes regimes such as an axisymmetric flow, a low helical state and a high helical mode are represented in the (Re, Ω) parameter plane.
Bulletin of the American Physical Society, Nov 25, 2014
Process (SSP) of Waleffe, like Hall's Vortex-Wave Interaction theory, was proposed as the fundame... more Process (SSP) of Waleffe, like Hall's Vortex-Wave Interaction theory, was proposed as the fundamental element of turbulence in low Reynolds number turbulence in wall-bounded shear flows and consists of three phases. (i) Streamwise vortices bend nd the streamwise velocity contours via advection. (ii) The undulating streamwise velocity leads to waviness in the vortices via Kelvin-Helmholtz instability. (iii) Nonlinear interaction of the wavy streamwise vortices promotes the streamwise vortices. We explore the SSP for Taylor-vortex flow, for which streamwise (azimuthal) and wavy vortices are genuine steady states resulting from linear instabilities with well-defined thresholds. In particular, we determine the circumstances under which wavy vortices reinforce Taylor vortices.
Bulletin of the American Physical Society, Nov 24, 2015
flows). Our facility is an extension of a classical plane Couette experiment, in which one uses a... more flows). Our facility is an extension of a classical plane Couette experiment, in which one uses a single closed loop of plastic belt to generate the opposite sign velocity at each wall of the test section. However, in our case, we use two independent closed loops of plastic belt, one at each wall of the test section. The speed of these belts may be controlled separately. That enables to set two different velocities (in value and direction) as a boundary conditions at each of two test section's walls. In addition the pressure gradient in streamwise direction can be controlled. In particular, the plane Poiseuille flow with zero mean advection velocity can be created. We characterize by PIV the basic flow for different configurations. For a plane Poiseuille flows as base flow, we were able to observe for the first time the nearly stationary turbulent spots in this flow, with structures of characteristic wavelength ∼ the distance between the two plates.
ANALES AFA, Sep 17, 2013
Se presentan los resultados experimentales sobre el comportamiento en funcion del tiempo de un tr... more Se presentan los resultados experimentales sobre el comportamiento en funcion del tiempo de un trazador inyectado en un flujo de Taylor-Couette sobre el que se superpuso un flujo axial continuo. Se trabajo con un equipo de Taylor-Couette de gap pequeno. La longitud es L=32cm, el radio del cilindro interior es de 45mm y el cociente entre los radios del cilindro interior y exterior es n=R1/R2=0.79. Se inyecto un pulso de fluorescencia a t=0 cerca del cilindro interior en la posicion L/2. Por medio de secuencias fotograficas se estudio la estabilidad y propagacion de los vortices de Taylor en funcion del caudal del flujo lateral. Con el objeto de estudiar la dispersion del trazador inyectado, se midio la concentracion del mismo en funcion del tiempo en el liquido efluente.
An experimental study of the velocity field structure of stationary Taylor Vortex Flow of Wide Ga... more An experimental study of the velocity field structure of stationary Taylor Vortex Flow of Wide Gap is performed by visualization in a range of high Reynolds numbers. The tracer dispersion in the flow field shows a short wavelength modulation throughout the structure.
Journal of Fluid Mechanics, Jan 29, 2019
The hairpin instability of a jet in a crossflow (JICF) for low jet-to-crossflow velocity ratio is... more The hairpin instability of a jet in a crossflow (JICF) for low jet-to-crossflow velocity ratio is investigated experimentally for a velocity ratio range of R ∈ (0.14, 0.75) and crossflow Reynolds numbers Re D ∈ (260, 640). From spectral analysis, we characterize the Strouhal number and amplitude of the hairpin instability as a function of R and Re D. We demonstrate that the dynamics of the hairpins is well described by the Landau model, and hence that the instability occurs through Hopf bifurcation, similarly to other hydrodynamical oscillators such as wake behind different bluff bodies. Using the Landau model, we determine the precise threshold values of hairpin shedding. We also study the spatial dependence of this hydrodynamical instability, which shows a global behaviour.
Physical review fluids, Sep 10, 2018
Physical Review E, Nov 14, 2011
The wake of a circular cylinder performing rotary oscillations is studied using hydrodynamic tunn... more The wake of a circular cylinder performing rotary oscillations is studied using hydrodynamic tunnel experiments at Re = 100. Two-dimensional particle image velocimetry on the mid-plane perpendicular to the axis of cylinder is used to characterize the spatial development of the flow and its stability properties. The lock-in phenomenon that determines the boundaries between regions of the forcing parameter space were the wake is globally unstable or convectively unstable (see [1] for a review) is scrutinized using the experimental data. A novel method based on the analysis of power density spectra of the flow allows us to give a detailed description of the forced wake, shedding light on the energy distribution in the different frequency components and in particular on a cascade-like mechanism evidenced for a high amplitude of the forcing oscillation. In addition, a calculation of the drag from the velocity field is performed, allowing us to relate the resulting force on the body to the wake properties.
Physical review fluids, Dec 21, 2018
The transition from Tayor vortex flow to wavy-vortex flow is revisited. The selfsustaining proces... more The transition from Tayor vortex flow to wavy-vortex flow is revisited. The selfsustaining process (SSP) of Waleffe [Phys. Fluids 9, 883 (1997)] proposes that a key ingredient in transition to turbulence in wall-bounded shear flows is a three-step process involving rolls advecting streamwise velocity, leading to streaks which become unstable to a wavy perturbation whose nonlinear interaction with itself feeds the rolls. We investigate this process in Taylor-Couette flow. The instability of Taylor-vortex flow to wavy-vortex flow, a process which is the inspiration for the second phase of the SSP, is shown to be caused by the streaks, with the rolls playing a negligible role, as predicted by Jones [J. Fluid Mech. 157, 135 (1985)] and demonstrated by Martinand et al. [Phys. Fluids 26, 094102 (2014)]. In the third phase of the SSP, the nonlinear interaction of the waves with themselves reinforces the rolls. We show this both quantitatively and qualitatively, identifying physical regions in which this reinforcement is strongest, and also demonstrate that this nonlinear interaction depletes the streaks.
Springer eBooks, 1984
Cellular structures in instabilities : An introduction.- Rayleigh-Benard instability : Experiment... more Cellular structures in instabilities : An introduction.- Rayleigh-Benard instability : Experimental study of the wavenumber selection.- Wavelength selection and pattern localization in buckling problems.- Wavenumber selection in buckling experiments.- Effect of boundaries on periodic patterns.- Cell number selection in Taylor-Couette flow.- Wavelength selection through boundaries in 1-D cellular structures.- Wavenumber selection in Rayleigh-Benard convective structure.- Convection patterns in large aspect ratio systems.- Three dimensional convective structttres in a horizontal or tilted porous layer.- Modelisation and simulation of convection in extended geometry.- Pattern evolution from convective and electrohydrodynamic instabilities.- Amplitude equations for non linear convection in high vertical channels.- Stability of cellular systems in Taylor-Couette instability.- Spatial dissipative structures and hydrodynamic instabilities.- Chemical structures far from equilibrium.- Structure defects in Benard-Marangoni instability.- Non adiabatic phenomena in cellular structures.- Smectics : A model for dynamical systems?.- Defects and interactions with the structures in ehd convection in nematic liquid crystals.- Quantitative study pf the disorganization of hexagonal convective structures.- Shear modes in low-prandtl thermal convection.- Spatial instabilities and temporal chaos.- Temporal and spatial aspects of the onset of chaos in a Taylor instability subjected to a magnetic field.- Electro-hydro-dynamical convective structures and transitions to chaos in a liquid crystal.- Rotating disk flows, transition to turbulence.- Morphological instabilities in the solidification front of binary mixtures.- Cellular structures on premixed flames in a uniform laminar flow.- Energy in the Benard-Rayleigh problem.- Modelisation of thermoconvective instabilities in saturated porous media- lateral boundary influence.- Competition between marangoni and archimedean forces, to determine the surface profile of a liquid heated, open to air.- Surface relief accompanying natural convection in liquid layers heated from below.- On the subject of Gortler vortex.
APS Division of Fluid Dynamics Meeting Abstracts, 2020
APS Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2015
Bulletin of the American Physical Society, Mar 4, 2020
arXiv (Cornell University), Aug 20, 2020
We report the results of an experimental investigation into the decay of turbulence in plane Coue... more We report the results of an experimental investigation into the decay of turbulence in plane Couette-Poiseuille flow using 'quench' experiments where the flow laminarises after a sudden reduction in Reynolds number Re. Specifically, we study the velocity field in the streamwise-spanwise plane. We show that the spanwise velocity containing rolls, decays faster than the streamwise velocity, which displays elongated regions of higher or lower velocity called streaks. At final Reynolds numbers above 425, the decay of streaks displays two stages: first a slow decay when rolls are present and secondly a more rapid decay of streaks alone. The difference in behaviour results from the regeneration of streaks by rolls, called the lift-up effect. We define the turbulent fraction as the portion of the flow containing turbulence and this is estimated by thresholding the spanwise velocity component. It decreases linearly with time in the whole range of final Re. The corresponding decay slope increases linearly with final Re. The extrapolated value at which this decay slope vanishes is Re az ≈ 656±10, close to Re g ≈ 670 at which turbulence is self-sustained. The decay of the energy computed from the spanwise velocity component is found to be exponential. The corresponding decay rate increases linearly with Re, with an extrapolated vanishing value at Re Az ≈ 688 ± 10. This value is also close to the value at which the turbulence is self-sustained, showing that valuable information on the transition can be obtained over a wide range of Re.
Bulletin of the American Physical Society, Nov 19, 2018
Bulletin of the American Physical Society, Nov 24, 2014
wake behind a sphere, rotating about an axis aligned with the streamwise direction, has been expe... more wake behind a sphere, rotating about an axis aligned with the streamwise direction, has been experimentally investigated in a water tunnel using LIF visualizations and PIV measurements. The measurements focused on the evolution of the flow regimes that appears depending of two control parameters, namely the Reynolds number Re and the dimensionless rotation or swirl rate Ω which is the ratio of the maximum azimuthal velocity of the body to the free stream velocity. In the present investigation, we covers the range of Re smaller than 400 and Ω from 0 and 1.5. Different wakes regimes such as an axisymmetric base flow, a low frequency frozen state, and an single and double helicoidal mode are represented in the (Re, Ω) parameter plane.
Bulletin of the American Physical Society, Nov 25, 2014
Submitted for the DFD14 Meeting of The American Physical Society Dynamic mode decomposition analy... more Submitted for the DFD14 Meeting of The American Physical Society Dynamic mode decomposition analysis of instability of the flow past rotating sphere MACIEJ SKARYSZ,
Journal of Physics D, May 31, 2000
The present article describes an experimental study of the dynamics of a small magnetic particle ... more The present article describes an experimental study of the dynamics of a small magnetic particle moving on the flat horizontal free surface of a rotating liquid and submitted to a magnetic field that decreases with distance from a dipole magnet. The particle is kept at the surface by interface forces and its motion is bidimensional. For a constant external force, its behaviour displays a transition at a threshold angular rotation velocity Ω = Ωc. Below the threshold, the particle remains at a fixed point; above the threshold, its trajectory tends towards a limit cycle of ovoidal shape and size increasing with Ω. A phenomenological modification of the equation that describes the motion of the particle is suggested in order to represent the influence of capillary effects on the particle trajectory: an effective drag coefficient is introduced that decreases the inertial response time of the particle. The numerical integration of the equation agrees with experimental observations. Nonlinear effects for a time-dependent magnetic field have been studied in the case of a square wave variation of frequency ω. The shape of the Poincare sections is shown to depend on the ratio ω/Ω. Starting from the disc angular coordinate, a circle map may be constructed which shows an almost one-dimensional behaviour.
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Papers by Jose E . Wesfreid