Papers by Sakir Amiroudine
The generation of waves near the interface of one or two liquid layers that is subjected to verti... more 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. Now
This is a fluid dynamics video submission of miscible and immiscible Faraday instability shot wit... more This is a fluid dynamics video submission of miscible and immiscible Faraday instability shot with a high speed camera.
This paper concerns the numerical study of the stability of a two-layer system filled with a sing... more 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. This instability is similar to the one of two
The hydrodynamic stability of a thermodiffusive interface in a near-supercritical fluid is studie... more 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 wavelengths are stabilized by diffusion.
The laminar field and heat transfer enhancement of forced convection in various counterflow porou... more The laminar field and heat transfer enhancement of forced convection in various counterflow porous channels with a joint aluminum plate was studied, using control volume technique and SIMPLE procedure for the velocity-pressure Coupling. Hydrodynamic and heat transfer results are reported for three configurations: (1) nonporous channels (NPC) (2) both channels filled by porous structure (BPC), and (3) only the channel contains hot fluid, filled by porous structure and other one is nonporous (HPC). The effectiveness, pressure drop and temperature difference are evaluated for wide ranges of Darcy, Reynolds and Prandtl numbers, also effects of thermal conductivity ratio is considered. The results show that as the Darcy, Reynolds or Prandtl number decreases, an increase in effectiveness is obtained. Also increase of thermal conductivity ratio causes to different effects on effectiveness in each case.
Physical Review E, 2010
In this paper, a lattice kinetic algorithm is presented to simulate nonisothermal magnetohydrodyn... more 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 vector kinetic equation. The distribution functions are only coupled via the macroscopic density, momentum, magnetic field, and temperature computed at the lattice points. The novelty of the work is the computation of the thermal field in conjunction with the hydromagnetic fields in the lattice Boltzmann framework. A 9-bit two-dimensional (2D) lattice scheme is used for the numerical computation of the hydrodynamic and thermal fields, whereas the magnetic field is simulated in a 5-bit 2D lattice. Simulation of Hartmann flow in a channel provides excellent agreement with corresponding analytical results.
Physics of Fluids, 2006
A numerical study of the stability in a two-layer system filled with a single pure supercritical ... more 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 instability is similar to the one of two miscible fluids
Physical Review E, 2012
The stability of a free surface under electro-osmotic flow in thin liquid films is investigated w... more 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 configuration gives some interesting insights into the physics of free surface stability at a scale where various competing forces such as the Coulombic force, van der Waals force, and surface tension come into play. The effects of the mentioned forces are incorporated in the Navier-Stokes equations and a linear stability analysis of the resulting governing equations is performed to obtain the Orr-Sommerfeld equations. The characteristic stability curve of the system is obtained through an asymptotic analysis of the Orr-Sommerfeld equations in the long wave limit. In this study, special focus is given to the effect of the interfacial zeta potential on the free surface stability. It is found that when the free surface and the substrate zeta potential have the same polarity the system is unstable. Since the strength of the free surface potential depends upon the nature of the fluid substrate interaction, this study can help in choosing a proper combination of fluid and substrate to design microfluidic and nanofluidic channels with a desired flow rate without triggering the interfacial instability.
Numerical Heat Transfer, Part A: Applications, 2010
The effect of thermal buoyancy on the upward flow and heat transfer characteristics around a heat... more 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 = 0.02 and 0.25. The flow shows unsteady periodic nature in the chosen
Journal of Fluid Mechanics, 2009
ABSTRACT
Journal of Fluid Mechanics, 1996
The mechanisms of heat and mass transport in a side-heated square cavity filled with a near-criti... more 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, finite-volume method. The results have revealed some striking behaviour compared with that obtained for normally compressible gases : (i) heat equilibration is still achieved rapidly, as under zero-g conditions, by the Piston Effect before convection has time to enhance heat transport; (ii) mass equilibration is achieved on a much longer time scale by quasi-isothermal buoyant convection; (iii) due to the very high compressibility, a stagnation-point effect similar to that encountered in highspeed flows provokes an overheating of the upper wall; and (iv) a significant difference to the convective single-roll pattern generated under the same conditions in normal CO, is found, in the form of a double-roll convective structure.
Journal of Fluid Mechanics, 2001
An analysis of the hydrodynamic stability of a fluid near its near critical pointinitially at res... more An analysis of the hydrodynamic stability of a fluid near its near critical pointinitially at rest and in thermodynamic equilibrium -is considered in the Rayleigh-Bénard configuration, i.e. heated from below. The geometry is a two-dimensional square cavity and the top and bottom walls are maintained at constant temperatures while the sidewalls are insulated. Owing to the homogeneous thermo-acoustic heating (piston effect), the thermal field exhibits a very specific structure in the vertical direction. A very thin hot thermal boundary layer is formed at the bottom, then a homogeneously heated bulk settles in the core at a lower temperature; at the top, a cooler boundary layer forms in order to continuously match the bulk temperature with the colder temperature of the upper wall. We analyse the stability of the two boundary layers by numerically solving the Navier-Stokes 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 with respect to the results of the theoretical stability analyses available in the literature and stability diagrams are derived. By accounting for the piston effect the present results can be put within the framework of the stability analysis of Gitterman and Steinberg for a single layer subjected to a uniform, steady temperature gradient.
International Communications in Heat and Mass Transfer, 2010
A two-dimensional numerical simulation is carried out to understand the effects of thermal buoyan... more 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 ...
Geothermics, 2013
The laminar field and heat transfer enhancement of forced convection in various counterflow porou... more The laminar field and heat transfer enhancement of forced convection in various counterflow porous channels with a joint aluminum plate was studied, using control volume technique and SIMPLE procedure for the velocity-pressure Coupling. Hydrodynamic and heat transfer results are reported for three configurations: (1) nonporous channels (NPC) (2) both channels filled by porous structure (BPC), and (3) only the channel contains hot fluid, filled by porous structure and other one is nonporous (HPC). The effectiveness, pressure drop and temperature difference are evaluated for wide ranges of Darcy, Reynolds and Prandtl numbers, also effects of thermal conductivity ratio is considered. The results show that as the Darcy, Reynolds or Prandtl number decreases, an increase in effectiveness is obtained. Also increase of thermal conductivity ratio causes to different effects on effectiveness in each case.
Computers & Fluids, 2010
A systematic study for the flow around a row of five square cylinders placed in a side-by-side ar... more 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 NavierStokes ...
Biomedical Microdevices, 2011
A comprehensive non-isothermal Lattice Boltzmann (LB) algorithm is proposed in this article to si... more 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 force evolved out as a consequence of the interaction between applied electric and magnetic fields. The fluid flow and thermal characteristics of the MHD micropump depend on several factors such as the channel geometry, electromagnetic field strength and electrical property of the conducting fluid. An involved analysis is carried out following the LB technique to understand the significant influences of the aforementioned controlling parameters on the overall transport phenomena. In the LB framework, the hydrodynamics is simulated by a distribution function, which obeys a single scalar kinetic equation associated with an externally imposed electromagnetic force field. The thermal history is monitored by a separate temperature distribution function through another scalar kinetic equation incorporating the Joule heating effect. Agreement with analytical, experimental and other available numerical results is found to be quantitative.
This article presents a two-dimensional numerical study on the unsteady laminar mixed convection ... more 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 separation ratios (spacing to cylinder size ratio, s/d)
Advances in Space Research, 1998
Phenomena in near critical fluids has recently led to important the0retica.l and experimental res... more Phenomena in near critical fluids has recently led to important the0retica.l and experimental results, in particular the prediction and the evidence of a mode of heat eyuilihra.tion called the Piston Effect (PE). The numerical method uses a finite volume a.pproxima.tion based on the SIMPLER algorithm and it considers an acoustic filtering on the Piston-Effect time-scale. In the case of a. R.ayleigh-BCnard configuration (heated from below). different types of flows a.re shown to develop depending on the local Rayleigh numbers and on the proximity with the critical point. The types of flows at larger Rayleigh numbers than critical, exhibit plumes at the bottom while the cooled top layer gives rise to an unstable diffusive layer. 01998 COSPAR. Published by
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Papers by Sakir Amiroudine