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Papers by Daniel Henry

Physical Review E, 2012

This study is a linear stability analysis of the flows induced by ultrasound acoustic waves (Ecka... more This study is a linear stability analysis of the flows induced by ultrasound acoustic waves (Eckart streaming) within an infinite horizontal fluid layer heated from below. We first investigate the dependence of the instability threshold on the normalized acoustic beam width H b for an isothermal fluid layer. The critical curve, given by the critical values of the acoustic streaming parameter, A c , has a minimum for a beam width H b ≈ 0.32. This curve, which corresponds to the onset of oscillatory instabilities, compares well with that obtained for a two-dimensional cavity of large aspect ratio [A x = (length/height) = 10]. For a fluid layer heated from below subject to acoustic waves (the Rayleigh-Bénard-Eckart problem), the influence of the acoustic streaming parameter A on the stability threshold is investigated for various values of the beam width H b and different Prandtl numbers Pr. It is shown that, for not too small values of the Prandtl number (Pr > Pr l), the acoustic streaming delays the appearance of the instabilities in some range of the acoustic streaming parameter A. The critical curves display two behaviors. For small or moderate values of A, the critical Rayleigh number Ra c increases with A up to a maximum. Then, when A is further increased, Ra c undergoes a decrease and eventually goes to 0 at A = A c , i.e., at the critical value of the isothermal case. Large beam widths and large Prandtl numbers give a better stabilizing effect. In contrast, for Prandtl numbers below the limiting value Pr l (which depends on H b), stabilization cannot be obtained. The instabilities in the Rayleigh-Bénard-Eckart problem are oscillatory and correspond to right-or left-traveling waves, depending on the parameter values. Finally, energy analyses of the instabilities at threshold have indicated that the change of the thresholds can be connected to the modifications induced by the streaming flow on the critical perturbations.

We consider the unsteady regimes of an acoustically-driven jet that forces a recirculating flow t... more We consider the unsteady regimes of an acoustically-driven jet that forces a recirculating flow through successive reflections on the walls of a square cavity. The specific question being addressed is to know whether the system can sustain states of low-dimensional chaos when the acoustic intensity driving the jet is increased, and, if so, to characterise the pathway and underlying physical mechanisms. We adopt two complementary approaches, both based on data extracted from numerical simulations: (i) We first characterise successive bifurcations through the analysis of leading frequencies. Two successive phases in the evolution of the system are singled out in this way, both leading to potentially chaotic states. The two phases are separated by a drastic simplification of the dynamics that immediately follows the emergence of intermittency. The second phase also features a second intermediate state where the dynamics is simplified due to frequency-locking. (ii) Nonlinear time series...

Une étude de la convection naturelle en cavité confinée différentiellement chauffée a été menée. ... more Une étude de la convection naturelle en cavité confinée différentiellement chauffée a été menée. Les rapports d'aspect de cette cavité, A w = W H = 1 6 et A l = L H = 10 6 , sont choisis de manière à correspondre à ceux du montage expérimental 'AFRODITE'. L'incapacité des modèles 2D à prédire de bons résultats en termes de champs de température et de vitesses par rapport à une étude 3D complète a tout d'abord été montrée. Deux modèles 2D 1/2 sont ensuite repris ici. Contrairement au modèle 2D, leur formulation prend en compte le frottement induit par les parois latérales de la cavité. Les résultats obtenus par les différents modèles 2D, 2D 1/2 et 3D sont comparés. On montre que pour les faibles nombres de Prandtl, et ce pour différents nombres de Grashof, le modèle 2D 1/2 , avec un choix adéquat du type de profil transverse de vitesse considéré, peut se substituer au modèle 3D. Abstract A study of the natural convection in a differentially heated cavity is presen...

The aim of this work is to examine the effect of the rotation on the flow generated by a horizont... more The aim of this work is to examine the effect of the rotation on the flow generated by a horizontal temperature gradient in a three-dimensional cavity. The rotation, through the action of the Coriolis force, induces a decrease of the main longitudinal flow, with a concomitant increase of the originally weak transverse velocity. This effect is particularly pronounced in the core of the cavity, which was the original region of main flow. As a result, the overall flow structure is changed. The initial well symmetric single roll flow is first deviated towards a diagonal of the cavity, with only the central symmetry kept. At larger rotation rates, in an asymptotic domain where all the velocity components eventually decrease, the 23 Congrès Français de Mécanique Lille, 28 au 1 Septembre 2017 longitudinal circulation is maintained in two rolls along the front and back lateral walls, while mainly transverse transfers occur in the core between these rolls. Finally, a 1D simplified model whic...

This paper focuses mainly on the investigation of the fluid flow and convective heat transfer ins... more This paper focuses mainly on the investigation of the fluid flow and convective heat transfer inside a two-dimensional double constricted channel employing the Lattice Boltzmann Method with multiple relaxation times (LBM-MRT). To describe the fluid behavior and the heat transfer, a detailed study was performed to interpret the effect of the constriction part and the Reynolds number variation using the D2Q9 and the D2Q5 model. A detailed study was performed to interpret the effect of the constriction part and the Reynolds number variation. The results are presented in the form of streamlines, isotherms and averaged Nussel number.

Physical Review Fluids

This paper deals with buoyant convection generated by a horizontal gradient of temperature in an ... more This paper deals with buoyant convection generated by a horizontal gradient of temperature in an infinite fluid layer, which is known as Hadley circulation, and studies the effects induced by applying a rotation around the vertical axis. First, the basic flow profile with rotation is derived and the influence of the rotation is depicted: The original longitudinal velocity profile is decreased in intensity when rotation is applied and its structure is progressively changed, whereas a transverse velocity component is created, which increases with the rotation intensity, overcomes the longitudinal velocity, and eventually decreases. Different asymptotic behaviors for these profiles have also been highlighted. The stability of these flows is then studied. The effects of the Prandtl number, the Taylor number, and the thermal boundary conditions are highlighted for the three types of instability occurring in such a situation (shear, oscillatory, and Rayleigh instabilities). It is observed that they are all stabilized by the rotation and that the increase of the critical thresholds is accompanied by a spinning of the wave vector corresponding to a progressive change of the orientation of the marginal perturbation rolls. Energy budgets are finally used to analyze the instability mechanisms.

Int J Heat Mass Transfer, 1994

Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 1997

ABSTRACT

EPJ Web of Conferences

The present work is intended to experimentally study the Taylor-Couette flow between coaxial cone... more The present work is intended to experimentally study the Taylor-Couette flow between coaxial cones. The inner cone is rotated and the outer cone is maintained fixed. Both cones have the same apex angle ĭ =12°, giving a constant annular gap į =0.12. The height of the fluid column is H=155 mm. The working fluid is assumed as Newtonian and has constant properties (as density and viscosity) within the range of the required experimental conditions. By means of visualization techniques, the critical thresholds related to the onset of various instabilities have been obtained and the corresponding flow modes have been identified. Using images processing, spatio-temporal diagrams have also been calculated, showing the characteristics (wavelength, drift velocity) of the downward helical motion. The results obtained for these transition regimes are compared to those of Wimmer et al. [1-3].

Water Resources Research, 2012

ABSTRACT The convection induced by buoyancy effects in a porous square cavity has been investigat... more ABSTRACT The convection induced by buoyancy effects in a porous square cavity has been investigated numerically using a spectral element code with bifurcation tools. The complex bifurcation diagram initiated from the first six primary bifurcation points corresponding to the onset of convection from the trivial no-flow solution has been calculated. Four branches of stable steady solutions have been found, corresponding to one-roll, two-roll, three-roll and four-roll flow structures. The domain of existence of these stable solutions, i.e., the Rayleigh number (Ra) range in which such solutions can potentially be observed, has been precisely determined. It is shown that there exist Ra ranges where different flow solutions can be stable together. The stable branches all terminate at Hopf bifurcation points beyond which oscillatory solutions have been computed.

International Journal of Thermal Sciences, 2013

Numerical simulations of stationary thermal convection in a differentially heated enclosure corre... more Numerical simulations of stationary thermal convection in a differentially heated enclosure corresponding to the AFRODITE solidification benchmark experiment [1e5] are presented. The cavity of relative dimensions 10:6:1 (length:height:width) is characterized by a small transverse width. The Prandtl number Pr is varied within the range [0.0045, 0.03], typical of liquid metals, whereas the Grashof number, defined as Gr ¼ gb(Dq/L)H 4 /n 2 , is varied within the range [1.3 Â 10 6 , 1.6 Â 10 7 ]. As shown by the reference 3D simulations, the temperature field in these situations is 2D (independent of the transverse direction); 2D simulations are, however, not able to catch the physics of the flow and the resulting temperature results are also erroneous. To improve these 2D simulation results while keeping reasonable computational times, a 2D½ model is developed, which will take into account the no-slip condition at the side walls. This model is obtained by averaging the governing equations over the width of the domain, with a transverse profile for the velocity featuring a uniform central part and two boundary layers of size d (d is fixed for the whole domain). The relative deviation of the temperature field between the 2D½ and 3D computations is investigated as a function of the Prandtl number, the Grashof number and the chosen boundary layer thickness. It is shown that an optimum value exists for d, which gives a mean deviation in the middle plane of less than 2%, whereas the choice of a more usual parabolic profile would lead to a twice larger deviation. Good comparisons are also obtained with the original experimental results reported at the end of the paper. The 2D½ model is thus able to give results which compare well with fully 3D results. It can then be used for extensive parametric studies at a reasonable cost.

congress.cimne.upc.es

The presence of salt influences the groundwater dynamics in a number of environmentally important... more The presence of salt influences the groundwater dynamics in a number of environmentally important problems such as saltwater intrusion in exploited coastal aquifers or aquifers overlying salt formations. In these situations, salt induced destabilizing density ...

Planning For Higher Education, 1984