Sakir Amiroudine

• Professor
• Full Professor at University of Bordeaux

The pair of fluids, FC72- 1cSt silicone oil, exhibiting temperature-sensitive miscibility gap is considered in this study to investigate the classical Rayleigh-B\'enard-Marangoni (RBM) instability. The system of fluids is considered at distinct temperatures to elucidate the effect of the degree of miscibility between the two fluids. We employ a mod...

A novel phase field method is proposed to model the continuous transition of binary fluids exhibiting temperature sensitive miscibility gap, from immiscible state to miscible state via partially miscible states. The model is employed to investigate the isothermal single-mode Rayleigh-Taylor (RT) instability for binary fluids as the system temperatu...

This special issue presents recent advances on interfacial fluid dynamics, in link with the 11th conference of the International Marangoni Association organized in Bordeaux, France, on June 2023.

A numerical modelling of electrophoresis of dielectric particle is proposed under low and moderate homogeneous electric fields. As surface charge at the surface of the particle increases, nonlinear effects associated with surface conduction become more prominent. Current analytical methodologies addressing this issue employ asymptotic techniques, n...

The objective in the present work is to consider a simple example of instability of a conducting self-similar micro jet in the external electric field, which represents a prototype of some microfluidic instabilities. Salt from a point source is emitted into its own aquatic solution, which is subject to an external uniform velocity field together wi...

Based on the conservative phase field model developed by Lowengrub and Truskinovsky [Proc. R. Soc. London A 454, 2617 (1998)PRLAAZ1364-502110.1098/rspa.1998.0273] for almost incompressible liquid binary mixtures, we propose an extended scheme for studying immiscible/miscible liquids. Below a critical temperature Tc, the liquids are immiscible with...

This paper considers the mixing of two dielectric miscible viscous liquids with different electric permittivities bounded by solid walls in an external electric field normal to the interface of the liquids. The mutual diffusion of these two liquids leads to the formation of an unsteady self-similar 1D diffusion layer. This layer is found to be unst...

The objective in the present paper is to study binary fluids with phase field modeling coupled with Navier-Stokes equations. An extended free energy is proposed to account for the continuous path from immiscible to miscible states. We consider fluid pairs that are immiscible for temperatures below the critical one (consolute temperature) and miscib...

The ubiquity of two-phase systems has rendered them a subject of prime importance especially from numerical perspectives. Among several methods described in the literature, which are generally classified as sharp or diffuse interface methods, phase-field (diffuse interface) method has been at the paramount of several recent investigations owing to...

The case of a supercritical fluid heated from below (Rayleigh-Bénard) in a rectangular cavity is first presented. The stability of the two boundary layers (hot and cold) is analyzed by numerically solving the Navier-Stokes equations with a van der Waals gas and stability diagrams are derived. The very large compressibility and the very low heat dif...

Electro-hydrodynamic instabilities near a cation-exchange microgranule in an electrolyte solution under an external electric field are studied numerically. Despite the smallness of the particle and practically zero Reynolds numbers, in the vicinity of the particle, several sophisticated flow regimes can be realized, including chaotic ones. The obta...

Electro-hydrodynamic instabilities near a cation-exchange microgranule in an electrolyte solution under an external electric field are studied numerically. Despite the smallness of the particle and practically zero Reynolds numbers, in the vicinity of the particle, several sophisticated flow regimes can be realized, including chaotic ones. The obta...

Electro-hydrodynamic instabilities near a cation-exchange microgranule in an electrolyte solution under an external electric field are studied numerically. Despite the smallness of the particle and practically zero Reynolds numbers, in the vicinity of the particle, several sophisticated flow regimes can be realized, including chaotic ones. The obta...

Electro-hydrodynamic instabilities near a cation-exchange microgranule in an electrolyte solution under an external electric field are studied numerically. Despite the smallness of the particle and practically zero Reynolds numbers, in the vicinity of the particle, several sophisticated flow regimes can be realized, including chaotic ones. The obta...

Electro-hydrodynamic instabilities near a cation-exchange microgranule in an electrolyte solution under an external electric field are studied numerically. Despite the smallness of the particle and practically zero Reynolds numbers, in the vicinity of the particle, several sophisticated flow regimes can be realized, including chaotic ones. The obta...

Electro-hydrodynamic instabilities near a cation-exchange microgranule in an electrolyte solution under an external electric field are studied numerically. Despite the smallness of the particle and practically zero Reynolds numbers, in the vicinity of the particle, several sophisticated flow regimes can be realized, including chaotic ones. The obta...

Electro-hydrodynamic instabilities near a cation-exchange microgranule in an electrolyte solution under an external electric field are studied numerically. Despite the smallness of the particle and practically zero Reynolds numbers, in the vicinity of the particle, several sophisticated flow regimes can be realized, including chaotic ones. The obta...

Electro-hydrodynamic instabilities near a cation-exchange microgranule in an electrolyte solution under an external electric field are studied numerically. Despite the smallness of the particle and practically zero Reynolds numbers, in the vicinity of the particle, several sophisticated flow regimes can be realized, including chaotic ones. The obta...

Electro-hydrodynamic instabilities near a cation-exchange microgranule in an electrolyte solution under an external electric field are studied numerically. Despite the smallness of the particle and practically zero Reynolds numbers, in the vicinity of the particle, several sophisticated flow regimes can be realized, including chaotic ones. The obta...

Electro-hydrodynamic instabilities near a cation-exchange microgranule in an electrolyte solution under an external electric field are studied numerically. Despite the smallness of the particle and practically zero Reynolds numbers, in the vicinity of the particle, several sophisticated flow regimes can be realized, including chaotic ones. The obta...

We investigate the electrophoresis of an ion-selective microgranule in an electrolyte solution. A semianalytical analysis of a small length of the electric double layer as well as overlimiting and extreme overlimiting currents is complemented by the direct numerical study of the full nonstationary Nernst-Planck-Poisson-Stokes system, with the corre...

The type of numerical scheme used in numerical computation of fluid flow largely affects the accuracy of the solution. In order to obtain accurate numerical solution in a transient analysis, implicit schemes are known to be unconditionally stable for linear systems while non-linearity in advection systems often limits the stability. Nevertheless, t...

Supercritical fluids (SCFs) are known to exhibit anomalous behavior in their thermophysical properties such as diverging compressibility and vanishing thermal diffusivity on approaching the critical point. This behavior leads to a strong thermomechanical coupling when SCFs are subjected to simultaneous thermal perturbation and mechanical vibration....

The instability of an electrolyte surface to a high-frequency, 10 to 200kHz, electric field, normal to the interface is investigated theoretically. From a practical viewpoint, such a high frequency leads to the absence of undesired electrochemical reactions and provides an additional control parameter. The theory of unsteady electric double layer b...

The type of numerical scheme used in numerical computation of fluid flow largely affects the accuracy of the solution. In order to obtain accurate numerical solution in a transient analysis, implicit schemes are known to be unconditionally stable for linear systems while non-linearity in advection systems often limits the stability. Nevertheless, t...

Experiments characterizing the influence of gravity and interfacial tension on Faraday instability in immiscible, confined fluid layers are presented. The variation in interfacial tension was obtained by controlling the temperature of a suitable binary fluid pair while the influence of gravity was analyzed through a series of terrestrial and microg...

Electrokinetics and the movement of charge-selective micro-granules in an electrolyte solution under the influence of an external electric field are investigated theoretically. Straightforward perturbation analysis is applied to a thin electric double layer and a weak external field, while a numerical solution is used for moderate electric fields....

Supercritical fluids when subjected to simultaneous quench and vibration have been known to cause various intriguing flow phenomena and instabilities depending on the relative direction of temperature gradient and vibration. Here we describe a surprising and interesting phenomenon wherein temperature in the fluid falls below the imposed boundary va...

The phenomenon of piston effect is well known in supercritical fluids wherein the thermal homogenization of the bulk occurs on a very short time scale due to pressure change caused by expansion or contraction of the fluid in the thermal boundary layer. In this article, we highlight an interesting phenomenon wherein by the application of external fo...

The stability of the electroosmotic flow of the two‐phase system electrolyte‐dielectric with a free interface in the microchannel under an external electric field is examined theoretically. The mathematical model includes the Nernst‐Plank equations for the ion concentrations. The linear stability of the one‐dimensional non‐stationary solution with...

The forces acting on a solid body just at the time of impact on the surface of a medium with very low compressibility, such as water, can be quantified at acoustic time scales. This is necessary in wide range of applications varying from large-scale ship designs to the walking or running mechanisms of small creatures such as the basilisk lizard. In...

The case of a supercritical fluid heated from below (Rayleigh-Bénard) in a rectangular cavity is first presented. The stability of the two boundary layers (hot and cold) is analyzed by numerically solving the Navier-Stokes equations with a van der Waals gas and stability diagrams are derived. The very large compressibility and the very low heat dif...

The stability of a system of two thin liquid films under AC electroosmotic flow is studied using linear stability analysis for long-wave disturbances. The system is bounded by two rigid plates which act as substrate. Boltzmann charge distribution is assumed for the two electrolyte solutions. The effect of van der Waals interactions in these thin fi...

The two-phase microflow of conductive (electrolyte) and non-conductive (dielectric) viscous liquids bounded by two solid walls in an external electric field is scrutinized. The lower solid wall, which is adjoined to the electrolyte, is a charged dielectric surface; the upper wall which bounds the dielectric is insulated. The problem has a steady on...

In this study the dynamics and stability of thin and electrically conductive aqueous films under the influence of a time-periodic electric field are explored. With the help of analytical linear stability analysis for long wavelength disturbances, the stability threshold of the system as a function of various electrochemical parameters and transport...

Lab-on-chip devices employ electro-osmotic flow (EOF) for transportation and mixing of liquids. However, when a steady (DC) electric field is applied to the liquids, there are undesirable effects like degradation of sample, electrolysis, bubble formation etc. due to large magnitude of electric potential required to generate the flow. These effects...

The Debye-Huckel approximation is generalized to the case of two-phase flows. A one-dimensional steady solution describing electroosmotic flow is found, and, for the first time, its linear stability is investigated analytically.

The Faraday instability arising in distinct miscible fluid layers, when the parametric forcing is parallel to the gravity vector, is analysed. A time-dependent density gradient is established from the moment the fluid layers are placed in contact with one another. The operating parameters in a miscible Faraday system are the frequency of parametric...

Instabilities of the interface between two thin liquid films under DC electroosmotic flow are investigated using linear stability analysis followed by an asymptotic analysis in the long-wave limit. The two-liquid system is bounded by two rigid plates which act as substrates. The Boltzmann charge distribution is considered for the two electrolyte so...

The instability of ultra-thin films of an electrolyte bordering a dielectric gas in an external tangential electric field is scrutinized. The solid wall is assumed to be either a conducting or charged dielectric surface. The problem has a steady one-dimensional solution. The theoretical results for a plug-like velocity profile are successfully comp...

A new kind of instability caused by Joule heating near charge-selective surfaces (permselective membranes, electrodes, or systems of micro- and nanochannels) is investigated theoretically using a model based on the Rubinstein-Zaltzman approach. A simple relation is derived for the marginal stability curves: Joule heating can either destabilize or s...

Large bubbles of oxygen are magnetically levitated inside a liquid column of oxygen. Then the magnetic field is rapidly quenched resulting in the formation of a geyser. This configuration reproduces the conditions of rocket re-ignition in orbit. Two bubbles with fill factors 6 % and 15 % were used. Two-dimensional numerical simulations based on VOF...

We investigate numerically the effect of a linearly polarized, harmonic vibration on a 2-D incompressible fluid confined in a square cavity when a sudden change of temperature is imposed at the walls under zero static gravity. A thermal front propagates from the wall, which can become unstable and develop as fingers. The study is performed in the f...

Electro-osmotic flows have seen remarkable applications in lab-on-a-chip based microdevices owing to their lack of moving components, durability and non-dispersive nature of the flow profiles under specifically designed conditions. However, such flows may typically suffer from classical Faradaic artifacts like electrolysis of the solvent which affe...

The main objective of the present work is to model the trans-critical path from supercritical to subcritical states near the critical point. The model is based on full compressible sets of equations. The pressure, temperature and density fields are determined in a Lagrangian form through the divergences of velocity and heat flux and advected afterw...

Experiments on near-critical hydrogen have been conducted under magnetic compensation of gravity to investigate the Faraday instability that arises at the liquid-vapor interface under zero-gravity conditions. We investigated such instability in the absence of stabilizing gravity. Under such conditions, vibration orients the interface and can destab...

The frozen-wave instability which appears at a liquid-vapor interface when a harmonic vibration is applied in a direction tangential to it has been less studied until now. The present paper reports experiments on hydrogen (H2) in order to study this instability when the temperature is varied near its critical point for various gravity levels. Close...

Hydrodynamics of near-critical fluids have gained considerable interest since the identification of the thermo-acoustic effect, an effect responsible for a fast thermal equilibration in a cell heated at one boundary [1, 2, 3]. Transport coefficients exhibit strong deviations near the critical point (CP). They are characterized by large density (ali...

This paper addresses the coupled heat and mass transfer in a one-dimensional porous medium saturated with a van der Waals supercritical fluid and subjected to a boundary heat flux. This one-dimensional study is the basis and preparatory step in order to outline all the new physics involved in this study before a complete two or three dimensional in...

Under the absence of gravity forces, the interaction of vibration with a thermal boundary layer (TBL) can lead to a rich variety of dynamics in a supercritical fluid (SCF). When subjected to vibration, a SCF can display different kinds of instabilities for different relative directions of the TBL and vibration. Rayleigh vibrational instability is f...

Multiphase flow control is a challenging task in microfluidic systems. Application of such ideas in electro-osmotic actuation of multiphase flows, which involves a complex convolution of phenomena ranging from electro-chemistry to hydrodynamics, is even more tricky. Most of the existing studies in the field have limited their scope to the thin elec...

The effect of vibrations on a stability of thermal wave propagating from rigid wall under a sudden change of the wall temperature is studied. The study is performed in the framework of the Boussinesq approximation where the density variations are taken into account only in the inertia force in the equations written in the reference frame of contain...

This article presents a two-dimensional numerical study on the unsteady laminar mixed convection heat transfer from a row of five in-line isothermal square cylinders placed in an unconfined medium and subjected to cross-flow of a Newtonian fluid at low Reynolds number (Re = 125). The hydrodynamic and thermal transport phenomena are captured for the...

The stability of a free surface under electro-osmotic flow in thin liquid films is investigated where the film thickness can be varied over the scale of a thick to thin electrical double layer while considering the relative contribution from the van der Waals forces. The role of interfacial Maxwell stress on thin film stability is highlighted. This...

The mixing between two miscible liquids subject to vertical vibrations is studied by way of experiments and a two-dimensional numerical model. The experimental setup consisted of a rectangular cell in which the lighter fluid was placed above the denser one. The diffuse interface was then visualized by a high-speed camera. After an initial period of...

Several weightless experiment with supercritical fluids have shown that thermal boundary layers can be destabilized when submitted to a harmonic vibration. A study of the phenomenon is given here in a regular fluid during a sudden change of wall temperature in the presence of harmonic tangential vibrations and under weightlessness. A semi-infinite...

The generation of waves near the interface of one or two liquid layers that is subjected to vertical vibrations is known as the Faraday instability. This instability occurs on account of a resonance that is set up when there is a tuning of the imposed frequency with the natural frequency of the free surface which possesses surface potential energy....

This is a fluid dynamics video submission of miscible and immiscible Faraday instability shot with a high speed camera. Comment: There is a video included

A comprehensive non-isothermal Lattice Boltzmann (LB) algorithm is proposed in this article to simulate the thermofluidic transport phenomena encountered in a direct-current (DC) magnetohydrodynamic (MHD) micropump. Inside the pump, an electrically conducting fluid is transported through the microchannel by the action of an electromagnetic Lorentz...

The effect of thermal buoyancy on the upward flow and heat transfer characteristics around a heated/cooled circular cylinder is studied. A two-dimensional finite-volume model is deployed for the analysis. The influence of aiding/opposing buoyancy is studied for the range of parameters −0.5 ≤ Ri ≤ 0.5, 50 ≤ Re ≤ 150, and the blockage ratios of B = 0...

In this paper, a lattice kinetic algorithm is presented to simulate nonisothermal magnetohydrodynamics in the low-Mach number incompressible limit. The flow and thermal fields are described by two separate distribution functions through respective scalar kinetic equations and the magnetic field is governed by a vector distribution function through...

A systematic study for the flow around a row of five square cylinders placed in a side-by-side arrangement and normal to the oncoming flow at a Reynolds number of 150 is carried out through the numerical solution of the two-dimensional unsteady incompressible Navier–Stokes equations. Special attention is paid to investigate the effect of the spacin...

A two-dimensional numerical simulation is carried out to understand the effects of thermal buoyancy and Prandtl number on flow characteristics and mixed convection heat transfer over two equal isothermal square cylinders placed in a tandem arrangement within a channel at low Reynolds numbers. The spacing between the cylinders is fixed with four wid...

This paper presents the unsteady laminar forced convection heat transfer from a row of five isothermal square cylinders placed in a side-by-side arrangement at a Reynolds number of 150. The numerical simulations are performed using a finite volume code based on the PISO algorithm in a collocated grid system. Special attention is paid to investigate...

A study of the Faraday instability of diffuse interfaces between pairs of miscible liquids of different densities, by means of experiments and by a nonlinear numerical model, is presented. The experimental set-up consisted of a rectangular cell in which the lighter liquid was placed above the denser one. The cell in this initially stable configurat...

Low amplitude, high frequency vibrations can induce in fluids under weightlessness behaviors that resemble those induced by gravity. Supercritical fluids (above their gas-liquid critical point) are used in the space industry and also display universal behavior. They are particularly sensitive to gravity effects. When submitted to vibration (typical...

Nous avons modélisé numériquement la stabilité d'un système de deux couches d'un même fluide pur supercritique soumis à une différence de température initiale à l'interface. La grande compressibilité et la faible diffusivité thermique des fluides critiques entraînent une instabilité gravitationnelle de type Rayleigh-Taylor de la couche de diffusion...

This paper presents the mechanisms of heat and mass transport of 1D and 2D low Mach number, unsteady, viscous, low heat diffusing, hypercompressible Navier-Stokes equations of a van der Waals gas (CO2). The results have been focused on some striking behaviours compared to those obtained for normally compressible gases: i) heat equilibration is stil...

A numerical study of the stability in a two-layer system filled with a single pure supercritical fluid subjected to an initial temperature difference is performed. The very large compressibility and the very low heat diffusivity of near-critical fluids lead to a Rayleigh-Taylor-like gravitational instability of the heat diffusion layer. This instab...

This paper concerns the numerical study of the stability of a two-layer system filled with a single pure supercritical fluid subjected to an initial temperature difference. The very large compressibility and the very low heat diffusivity of near-critical fluids lead to a Rayleigh-Taylor like gravitational instability of the heat diffusion layer. Th...

We numerically investigate the linear stability of two superposed near critical isobar fluid layers of variable thickness initially at two different temperatures. The very large compressibility and the very low heat diffusivity of near critical pure fluids induce very large density gradients which lead to a Rayleigh-Taylor-like (RTL) gravitational...

An acoustic filtering procedure [1] has been applied to fluids above their critical point in order to decrease computational costs. The Navier-Stokes equations coupled with the energy and linearized state equations have been considered in order to solve problems related to thermal instabilities in such fluids. In the vicinity of the critical point,...

A numerical solution of the Navier–Stokes equations coupled with the energy and linearised equation of state has been performed in the unsteady Rayleigh–Bénard configuration for nearly supercritical 3He in the exact conditions with which Meyer and Kogan (Phys. Rev. E 63 (2002) 056310) performed their experiments. We propose an interpretation of the...

We perform a Navier-Stokes numerical simulation of the transient Rayleigh-Bénard convection onset in nearly supercritical 3He in the exact conditions in experiments performed by Kogan, Murphy, and Meyer [Phys. Rev. Lett. 82, 4635 (1999)]Phys. Rev. E 63, 056310 (2001)]]. We find an interpretation of the observed unexpected temperature oscillations a...

temperature oscillations at the Rayleigh-Benard convection threshold in supercritical He 3 contained in a shallow cavity heated by a constant heat flux at the bottom wall, the top wall being maintained at its initial temperature. These oscillations have also been reproduced by numerical simulations by several independent groups in Japan (A. Onuki)...

An analysis of the hydrodynamic stability of a fluid near its near critical point is considered in the RayleighStokes equations appropriate for a van der Waals' gas slightly above its critical point. A finite-volume method is used together with an acoustic filtering procedure. The onset of the instabilities in the two different layers is discussed...

This work brings new insight to the question of heat transfer in nearStokes equations written for a low-heat-diffusing near-critical van der Waals fluid. They show that hydrodynamics greatly affects thermoacoustics in the vicinity of the upper thermostated wall, leading to a rather singular heat transfer mechanism. Heat losses through this wall gov...

The hydrodynamic stability of a near critical fluid initially at rest and at thermodynamic equilibrium in a 2D square cavity heated from below (Rayleigh-Bénard configuration) is studied. Due to the piston effect (specific to near critical fluids), the thermal field exhibits a very thin hot thermal boundary layer at the bottom and a cooler boundary...

The hydrodynamic stability of a thermodiffusive interface in a near-supercritical fluid is studied. The Navier-Stokes equations written for a van der Waals gas above its critical point are solved by means of a finite volume numerical method. The growth rate of the fluctuations shows that there exists a cutoff wave number beyond which the short wave...

Phenomena in near critical fluids has recently led to important theoretical and experimental results, in particular the prediction and the evidence of a mode of heat equilibration called the Piston Effect (PE). The numerical method uses a finite volume approximation based on the SIMPLER algorithm and it considers an acoustic filtering on the Piston...

This work brings new insight to the question of the piston effect, which has been found to be the main cause of temperature equilibration in the vicinity of the liquid–vapor critical point under weightlessness conditions. The thermalization process of a near-critical fluid confined in a cavity and submitted to local heating is modeled with special...

The hydrodynamic stability of a thermodiffusive interface in near supercritical fluid is studied. The Navier-Stokes equations written for a van der Waals gas set above its critical point are solved by means of a finite volume numerical method. The growth rate of the fluctuations shows that a cutoff wave number exists beyond which the short wave len...

The hydrodynamic stability of a thermodiffusive interface in near supercritical fluid is studied. The Navier-Stokes equations written for a van der Waals gas set above its critical point are solved by means of a finite volume numerical method. The growth rate of the fluctuations shows that a cutoff wave number exists beyond which the short wave len...

We present a number of algorithms using a finite volume method for solving the one-dimensional unsteady, low Mach number hypercompressible Navier-Stokes equations. Calculations are made, using the SIMPLE, SIMPLER and PISO algorithms, for fluids near their critical point which exhibit singularities in some of the physical properties. Of these the mo...

The mechanisms of heat and mass transport in a side-heated square cavity filled with a near-critical fluid are explored, with special emphasis on the interplay between buoyancy-driven convection and the Piston Effect. The Navier–Stokes equations for a near-critical van der Waals gas are solved numerically by means of an acoustically filtered, finit...