Convection naturelle en milieu poreux anisotrope: Effet du maximum de densite (French text).

摘要

Convective motion and heat transfer have a direct influence on the ice cover formation or suppression. Convective motion before the freezing or melting of ice constitutes a very important factor on the rate at which phase changes occur.; In this thesis, convection involving a maximum density (or penetrative convection) has been studied for the case of rectangular horizontal cavity filled with a porous medium anisotropic in permeability. The porous layer is saturated by cold water whose density varies in a nonlinear way with temperature, through a maximum value. The porous medium is modeled by the classical Darcy equations. Dirichlet boundary conditions (constant temperature) are applied to active boundaries.; Linear stability. The effect of the already mentioned control parameters on the critical Rayleigh number has been studied. Results obtained have shown that convection motion originates in the unstable layer at the bottom of the cavity (near the lower boundary), penetrates more and more in the upper part of the cavity (near the upper boundary) and ultimately reaches the upper boundary for γ ≥ 2.; The confinement effect has been studied by varying the aspect ratio of the cavity. In particular we have observed the absence of any type of symmetry when the principal axes are oblique and when the density maximum is located between the upper wall and the lower wall.; Finite amplitude convection. As a first step, we have considered the case of classical natural convection, reached asymptotically for γ 2. Results obtained in the case of a confined layer, with principal axes inclined at 45°, have revealed the existence of two different flows, one termed natural and the other termed anti-natural, the natural flow being the one toward which the system converges from no flow initial conditions.; A few typical results for the case of a nonlinear density-temperature relationship have revealed the existence of a subcritical bifurcation, i.e., the existence of convective motion below the critical Rayleigh number predicted by the linear stability analysis. (Abstract shortened by UMI.)