Mohammed El Ganaoui

Localisation d'un front de solidification en interaction avec un bain fondu instationnaire

Resume Linteraction de la convection thermique instationnaire dun bain fondu avec un front de solidification est etudiee numeriquement. Lapplication concerne la croissance cristalline par une technique de type Bridgman verticale. Le domaine physique comporte une zone liquide, une zone solide et une zone intermediaire de transition de petite dimension, modelisee comme un milieu poreux. Une formulation homogene de type enthalpie-porosite est proposee avec une approximation numerique de type volumes finis. Le modele permet la localisation du front de solidification et la description de ses deformations. La methode est qualifiee par rapport a une approche de suivi de front a differentes valeurs du nombre de Rayleigh.

Investigation of a side wall heated cavity by using lattice Boltzmann method

The lattice Boltzmann method based on the BGK model has been used to simulate laminar natural convection in a heated rectangular cavity on the uniform grid. The hydrodynamic and thermal fields are solved by using the double populations approach. A general benchmark has been carried out to show the effects of secondary parameters at their wide range. Excellent agreement is obtained by comparison with available literature.

Simulation nume´rique par une approche porosite´-enthalpie de la convection thermo-solutale dans une ampoule de croissance cristalline

Abstract The vertical Bridgman-Stockbarger technique is a directional solidification technique. The material is loaded into an ampoule, and solidified by varying the temperature field with a translation of the ampoule through a furnace. The hydrodynamic is governed by both solutal and thermal convective instabilities. The resolution of the problem uses an homogenised formulation of the conservation equations, the enthalpy approach, issued from classical mixture theories. The energy equation is formulated with the enthalpy variable. Solving the conservation equations in the whole domain allows not to track the interface, as its shape is not needed in the resolution. The numerical simulation is done using a finite-volume method. We present here studies on two type of Bridgman configurations. The first one is an inverted Bridgman configuration of a pure material. The results show the interaction between the interface and the hydrodynamic of the unsteady melt. The second is a solidification of a binary alloy, where the temperature gradient has a stabilising effect. The results show the influence of the convection on the distribution of dopant in the solidified crystal.

Near-Wall Models for Improved Heat Transfer Predictions in Channel Flow Applications

This work aims to improve the accuracy of the predicted temperature profile in the near-wall region of turbulent boundary layers. It is well known that practical understanding of turbulent boundary layers is central to heat transfer enhancement in many engineering applications. In one case, an eddy viscosity formulation based on a near-wall turbulent kinetic energy k+ function and the van Driest mixing length equation are used. In the second case, the turbulent Prandtl number is not assumed constant but rather is modeled by incorporating improved turbulent Prandtl number relations into existing models. The test case is the fully developed plane channel flow, which is considered to be the simplest and most idealized boundary-layer flow. These new formulations show improved agreement against the temperature profiles of direct numerical simulations of turbulent channel flow versus simulated cases using a commercial computational fluid dynamics package.