Bernard Roux

French National Centre for Scientific Research | CNRS · Modelisation en Mecanique et Procedes Prpres

The confluence of rivers is characterized by highly complex internal processes. The hydrodynamic aspects of river confluences have received a lot of attention in recent years. For modeling purposes, it is generally assumed that the water densities of the rivers under consideration are close, and the density effects associated with their difference...

Confluences are common components of all riverine systems, and are characterized by converging flow streamlines and mixing of separate flows, which can take some significant distance to be complete. Whilst turbulent diffusion and Taylor dispersion are expected to affect mixing in any open channel flow, the analysis of mixing at river confluences sh...

At present, a significant weakening of the intensity of transverse mixing at the confluence of large rivers, which is observed in a number of cases, is widely discussed. Since the observed features of the confluence of large watercourses are not only of research interest but also of significant economic importance associated with the characteristic...

Due to the shallowness, currents and hydrodynamics of Berre lagoon (South of France) are closely conditioned by the bottom topography, and wind affects the entire water column, as for many other Mediterranean lagoons (Perez-Ruzafa, 2011). Wind stress, which is caused by moving atmospheric disturbance, is known to have a major influence in lagoon wa...

Motion models of wave processes in the coastal zone are highly demanded in the projection and construction of coastal surface structures and breakwaters, and also as a component of other models. The most common of the grid approaches is currently vof-method. A significant drawback of this method is in the necessity to solve the convection equation...

The present study concerns the 3-D distribution of pollutants emitted from a coastal outfall in the presence of strong sea currents. The problem is solved using the nonlinear Reynolds-averaged Navier-Stokes equations in the framework of the k-ɛ model. The constants of the logarithmic law for the vertical velocity profile in the bottom boundary laye...

The paper addresses the application of the nonlinear hydrodynamics model (RANS (Reynolds-averaged Navier-Stokes) equations) in a wide semi-enclosed Mediterranean lagoon (Berre lagoon), considering three natural forcing functions, i.e., sea tide propagating through a long narrow channel, wind and runoff. Main attention is focused to characteristic v...

Pollutant distribution from a coastal outfall is studied accounting for tidal currents. The problem is solved using k-eps model. The constants in the logarithmic law for vertical velocity profile in the bbl (bottom boundary layer) are obtained by processing experimental data from a current profiler. The near-field distribution of pollutant concentr...

Shallow water reservoirs are complex multi-parameter hydrodynamic systems. The current and the coupled processes occurring in them are spatially three-dimensional and unsteady, and have essentially nonlinear character. Therefore, the use of field experiments to analyse such a systems is extremely labor intensive and costly. Without underestimating...

Parameterization of coefficient of vertical turbulent exchange plays important role in the hydrodynamics of shallow water basin. Relevant parameters are determined on the basis of ADCP in situ experiments. They are implemented in Azov3D package developed at TIT-Russia. They are used to determine the currents in shallow water basins: Etang de Berre,...

The effect of high-frequency rotational vibrations with small amplitude on the oriented crystallization of binary alloys has been numerically studied. The calculations have been made in the framework of the quasi-static approach for succinonitrile-acetone and succinonitrile-salol binary systems. It has been shown that at a large solidification rate...

The control of dopant segregation by accelerated crucible rotation was investigated for the vertical Bridgman growth of Ga-doped germanium crystals. The accelerated crucible rotation technique (ACRT) and the angular rotation technique (AVT) were considered. Both techniques were found effective in radial segregation control; however, ACRT generated...

The accelerated crucible rotation technique (ACRT) has been used extensively in crystal growth for the control of flow and segrega-tion. However, the amelioration of the spin-up and spin-down flows for a favorable growth has not yet been fully understood. In this study, we investigate several ACRT schemes and discuss their effects on the flow, inte...

The effects of accelerated crucible rotation technique (ACRT) on the segregation, interface shape, and morphological instability during vertical Bridgman (VB) crystal growth of succinonitrile (SCN) containing 0.064 wt% acetone were investigated by visualization experiments and computer simulation. It was found that ACRT was effective in reducing ti...

This paper deals with the effects of vibrations on the stability of a binary alloy solidifying at constant velocity under zero gravity conditions or in the presence of a static gravitational field. The density dependence of the solute concentration is accounted for through the Boussinesq approximation. In the first part of the paper, the effect of...

Double-diffusive and vibrational convection with the Soret effect is considered in a cubic rigid cell filled with water 90% and isopropanol 10%, subjected to a temperature difference between opposite lateral walls. Numerical simulations are carried out for g-jitter induced flow. The direction of g-jitter is the same as the residual gravity vector,...

Thermal–solutal flows and their induced segregation and supercooling are important in the growth of an alloy crystal. For the vertical Bridgman crystal growth having a stabilized thermal profile, in addition to the thermal convection induced by radial thermal gradients, solute gradients can either induce or suppress the flow depending on the solute...

The aim of this paper is to show the efficiency of a "combined" method proposed to solve the 2D incompressible Navier-Stokes equations in the vorticity and stream-function formulation. A compact hermitian scheme is used for the stream function equation while a classical second order accurate scheme is taken for the vorticity equation. Comparisons h...

The effect of angular vibration on the flow, segregation, and interface morphology during vertical Bridgman crystal growth was investigated. Transparent experiments using SCN containing about 0.02 wt.% acetone were performed. To simulate the observed results, both direct numerical simulation (DNS) and Schlichting boundary layer approximation (SBLA)...

This paper presents a summary of cellular and dendritic morphologies resulting from the upward directional solidification of Al - Ni alloys in a cylindrical crucible. We analysed the coupling of solid-liquid interface morphology with natural and forced convection. The influence of natural convection was first analyzed as a function of growth parame...

Three-dimensional buoyancy driven flows in vertical cylinders are simulated with a finite difference technique. Asymmetric convective flows are studied for three values of the (length-to-radius) aspect ratio A. One result concerns the occurrence of asymmetric convection in a flat A=0.485 cylinder for Pr=6.7, near the threshold and up to 3Ra~ (where...

The paper deals with the numerical investigation of the influence of static and vibrational acceleration on the measurement of diffusion and Soret coefficients in binary mixtures, in low gravity conditions. In space experiments, liquids with inhomogeneous composition are prepared by Soret diffusion under an imposed temperature gradient. So, the pro...

The paper presents the design and the first stage of implementation of the NumGRID middleware that is devoted to the development of the multicomputer grid software for the large scale numerical simulation. Global addressing of the NumGRID computational resources and MPI programs execution is provided. This stage is the basis for the development of...

Abstract We present methods for developing high performance,computational kernels and dense linear algebra routines. The microarchitecture of AMD processors is analyzed with the goal to achieve peak computational rates. Approaches for implementing,matrix multiplication algorithms are suggested for hierarchical memory,computers. Block versions of ma...

The paper deals with the vibration influence on the stability of a planar solidification front moving with constant average velocity. The case of high frequency vibrations with small amplitude is studied. The density dependence on the solute concentration is accounted for in the framework of the Boussinesq approach. The equations for average veloci...

Directional solidification of alloys, which allows the independent control of growth parameters (pulling velocity, temperature gradient), is an experimental method of choice for the investigation of many fundamental problems (e.g. microstructure formation and selection, segregation of chemical species) encountered in the processing of structural ma...

We analyzed the effects of both natural convection and forced flows on solid–liquid interface morphology during upward Bridgman solidification of metallic alloys. Experiments were carried out on Al–3.5 wt% Ni alloy, for a cylindrical sample. The influence of natural convection induced by radial thermal gradient on solidified microstructure was firs...

The modeling of air supply devices has been identified from the International Energy Agency (IEA) Annex 20 project as one of the most important problems in applying computational fluid dynamics (CFD) to predict air flow pattern and air distribution in buildings, and the complicated HESCO nozzle diffuser used in the IEA Annex 20 test room has been p...

During vertical Bridgman crystal growth, local solute accumulation along the freezing interface due to buoyancy often causes radial non-uniformity and pit formation, which accelerate morphological instability. A novel approach by using angular vibration has been proposed. Through the visualization of the freezing interface during directional solidi...

This work concerns the vibration influence on the stability and dynamics of fluid interfaces. Resonance phenomena (Faraday ripple, parametric waves under horizontal vibrations, the stability of the interface of liquid and its saturated vapor in the near critical state) are discussed. The thresholds of excitation of parametric resonance are determin...

The modeling of air supply devices has been identified from the IEA (International Energy Agency) Annex-20 project as one of the most important problems in applying computational fluid dynamics to predict air flow pattern and air distribution in buildings. In this paper, a simplified model for the modeling of the HESCO nozzle diffuser used in the I...

In this paper we present methods for developing high performance computational kernels and dense linear algebra routines. First, the microarchitecture of AMD Athlon processors is analyzed, with the goal to achieve peak computational rates. These processors are widely used for building inexpensive PC clusters. Then, different approaches for implemen...

We consider some methods of evaluating parallel performance on clusters and MPP platforms. These methods are based on using a parallel code for the numerical simulation of 3D incompressible viscous flow in a cylindrical domain. Details of the efficient parallelization of this code are discussed for distributed memory computers with relatively slow...

This paper deals with meniscus deformation and flow in an isothermal liquid bridge maintained between two circular rods, when one rod is subject to axial monochromatic vibrations. It concerns a fundamental aspect of the problem of crystal growth from melt by the floating-zone technique which is often considered in weightlessness conditions. In the...

Numerical investigation of a bubble immersed in a liquid of different density in a container subject to translational oscillations in weightlessness conditions shows the following scenario where the bubble, initially located at the container center, starts to move to the container wall due to an attraction mechanism having nonviscous origin. This m...

The paper deals with the analysis of the vibration influence on the dynamics of a two-phase system in zero gravity conditions. The influence of high frequency vibrations on the behavior of solids immersed in a liquid is analyzed. Mean forces and torques acting on the solids from oscillating liquid are determined from general equations of the liquid...

This paper describes a parallelization method for the numerical simulation of 3D incompressible viscous flow in a cylindrical domain. Implementation details are discussed for efficient parallelization on distributed memory computers with relatively slow communication links. The developed parallel code is used for the performance evaluation of sever...

Free oscillations of a viscous liquid drop surrounded by a dynamically inactive ambient gas, in zero gravity, are investigated numerically using FIDAPTM package in the axisymmetrical case. The full Navier-Stokes equations with appropriate interfacial conditions are solved by using Galerkin/Finite element technique along with the spine method for th...

A comparatively new possibility to influence convection in crystal growth melts is the application of controlled interface vibration, especially in systems with free melt surfaces like the float-zone process. The present paper concerns the development and testing of a vibrational device which will be integrated into a microgravity crystal growth fa...

A theoretical investigation of crystal growth shaping process (to elaborate crystals in the form of tubes or rods with different cross sections, and other complicated forms) is carried out on the basis of the dynamic stability concept. The capillary dynamic stability of shaped crystal growth from the melt is analyzed using a mathematical model base...

The stability of the interface separating two immiscible incompressible fluids of different densities and viscosities is considered in the case of fluids filling a cavity which performs horizontal harmonic oscillations. There exists a simple basic state which corresponds to the unperturbed interface and plane-parallel unsteady counter flows; the pr...

The paper presents methods for developing high performance computational cores and dense linear algebra routines. Different ap- proaches for performing matrix multiplication algorithms are analysed for hierarchical memory computers, taking into account their architec- tural properties and limitations. Block versions of matrix multiplication and LU-...

We study a non-isothermal two-phase flow in a closed cavity heated from the sidewall, where one of the phase is a gas (or a liquid) and another phase consists of solid particles. The particles are subjected to the gravitational precipitation and the drag exerted by the flow. In the framework of the generalized Boussinesq approximation we derive a c...

The averaged viscous incompressible fluid flow driven by a vibrating body with a large-curvature edge is investigated experimentally and numerically. The case of an axisymmetric body immersed in fluid and performing translational vibrations along its axis is considered. Experiments carried out on fluids of various viscosity over a wide vibration fr...

This paper concerns a numerical study of the flow characteristics of thermocapillary convection in a system composed of two immiscible liquid layers subject to a temperature gradient along their interface. We consider the two-layer system: B2O3 (encapsulant) and GaAs (melt), for its experimental relevance in crystal growth by the directional solidi...

The results of a numerical calculation of the unsteady shear flow of a viscous incompressible fluid in a cavity with moving lids are given for various geometries and values of the Reynolds number. The paper describes the numerical method developed for solving the three-dimensional unsteady Navier-Stokes equations in a regular domain and also the di...

This paper concerns the modeling of convective flows induced by vibration in a system imitating floating-zone crystal growth. Specific equations are used for the case of high-frequency vibrations. The zones of resonance excitation of the surface waves (to be avoided) are determined. Out of these zones, our numerical simulations show the coupled inf...

Vibrations exert significant influence on the behavior of heterogeneous systems. It is important for microgravity research to understand the detrimental effect of g-jitter on experiments on board the orbital space stations, like ISS, where different types of vibration can be found (translational vibrations of linear polarization; circular or ellipt...

Modeling and numerical simulations of the convective flows induced by the vibration of the monocrystal during crystal growth have been performed for two configurations simulating the Cz and FZ methods. This permitted to emphasize the role of different vibrational mechanisms in the formation of the average flows. It is shown that an appropriate comb...

We consider the instability of the steady, axisymmetric thermocapillary convection in cylindrical liquid bridges. Finite-difference method is applied to compute the steady axisymmetric basic solutions, and to examine their linear instability to three-dimensional modal perturbations. The numerical results show that for liquid bridges of O(1) aspect...

A theoretical investigation of the crystal growth shaping process is carried out on the basis of the dynamic stability concept. The capillary dynamic stability of shaped crystal growth processes for various forms of the liquid menisci is analyzed using the mathematical model of the phenomena in the axisymmetric case. The catching boundary condition...

Convective flows in a liquid bridge subject to axial high frequency vibrations are studied on the base of a generalized Boussinesq approach. The generation of mean vorticity in the dynamical skin-layers near the rigid and free boundaries is taken into account, with the help of effective boundary conditions for the mean components of hydrodynamical...

This paper concerns the influence of high frequency vibrations on interfaces (free surface of a fluid, interface of two immiscible fluids, surface of a solid body immersed in a liquid). Such interfaces are described by different equations and boundary conditions, but in all the cases they are oriented perpendicularly to the vibration axis.RésuméCet...

The paper describes different methods of performance optimization of serial and parallel algorithms for modern superscalar RISC processor based computers. The limitations imposed on the performance by hierarchical organization of computer memories are discussed, followed by the comparative performance analysis of different computers and their archi...

Parallel implementation of the well known method of reduction of Boundary Values Problem (BVP) for ODES to Initial Values Problem (IVP) with subsequent straightforward integration is discussed. As an example, the solution is obtained for a 2D linear stability problem with two superimposed viscous fluid layers in a plane horizontal cavity subjected...

The aim of this paper is to understand the thermal behaviour of filamentary fuses under space environment in order to optimise the derating rules. To reach this goal, two important phases compose the study : a theoretical model is computed and an experiment is performed to validate the first point.

The flow in the gap between two cylinders with the inner one subject to high frequency vibrations is investigated. The equations for the mean and pulsating components of hydrodynamical fields are formulated taking into account the pulsating transport of the mean vorticity. It is shown that in the case of oscillations of circular polarization, the m...

The g-jitter effects on the thermocapillary convection in liquid bridge of floating half zone were studied by numerical simulation for unsteady and axi-symmetric model in the cylindrical coordinate system. The g-jitter field was given by a steady microgravity field in addition to an oscillatory low-gravity field, and the effects on the flow field,...

This paper describes the numerical method of solution of 3D Navier-Stokes equations in a regular domain and direct method of parallelization of solution for distributed-memory computers. A vorticityvector -potential formulation and Finite Difference method of solution are chosen, using fractional step ADI method for vorticity equation and Fourier m...

Time-averaged flows induced by oscillations of a heated (or cooled) solid sphere immersed in a liquid are investigated. The cases of an infinite surrounding liquid and the liquid placed into the spherical rigid envelope are considered. The gravity is absent. The interaction of thermovibrational flows and vibrational Schlichting flows is studied. Ne...

We investigate two-dimensional thermal convection of saturating incompressible fluid in a horizontal cylinder filled with porous medium. The temperature distribution on the boundaries is time-independent and corresponds to the heating from below. At supercritical parameter values the problem has infinite number of stationary solutions for arbitrary...

The results of the dynamic stability investigation of the shaped crystal growth process obtained by Pet'kov and Red'kin [J. Crystal Growth 104 (1990) 20] are analyzed. The approach that they used has at least two errors and leads to unacceptable results.

Vibrational convective flows in a liquid bridge with a deformable free surface, heated by a ring radiator and subjected to axial high-frequency vibrations, have been studied theoretically. The shape of the free surface determined by the balance of capillary energy and energy of high frequency pulsations is defined by means of a variational principl...

Convective flows of a nonuniformly heated fluid in a cylindrical fluid zone in a high-frequency longitudinal vibration field are studied. Vibration frequencies which are high as compared with dissipative decrements and capillary frequencies, but small as compared with acoustic frequencies are considered. The general method formulated earlier for de...

To prepare the microgravity experiment of crystal growth by floating zone method, GEZON, numerical studies of hydro-dynamics of the melt are carried out. Calculations of zone length and convection driven by surface-tension gradients are presented for germanium floating zone operating under microgravity conditions. Results of linear stability analys...

Steady thermocapillary driven flows of two immiscible liquid layers based on liquid GaAs (lower layer) and B2O3 (upper layer) are studied numerically in the case of a cavity subjected to a horizontal temperature gradient. Both situations with rigid or with free top surface have been considered and the interfaces are assumed to be flat. The Navier-S...

In crystal growth autoclaves, dissolution zone and cristallisation zone are connected through a diaphragm. The flow regimes in such a configuration are quite complex, as they result from two buoyancy mechanisms, solutal and thermal, acting in opposite directions. In addition, the autoclave walls are thick and heat transfer in it strongly affect hea...

The effect of hight frequency vibration on the flow and temperature fields is studied numerically for two configurations: a two-dimensional square cavity and an axisymmetrical liquid zone, subject to an external temperature gradient. The mean fields of velocity and temperature are determined by means of a finite-element method, respectively. The ch...

In the present paper, liquid encapsulated floating zone melting of GaAs is modelled numerically. The system consists of two coaxial liquid columns (GaAs and B2O3) and are confined by the ampoule. The effect of encapsulation on capillary stability of the liquid bridges is investigated. Marangoni convection in GaAs melt is considerably reduced with t...

Heat exchanges in a sealed ampoule in the LTVG (low temperature vapour growth) furnace have been modelled in order to compute temperature fields and control the growth of HgI2 crystals from vapour phase at low temperatures. We use a coupled conductive-radiative model to determine the shapes of the source and the crystal at different equilibrium sta...