Thermoconvective instabilities in supercritical fluids

A numerical solution of the Navier-Stokes equations coupled with the energy and linearised equation of state has been performed in the unsteady Rayleigh-Benard configuration for nearly supercritical He-3 in the exact conditions with which Meyer and Kogan (Phys. Rev. E 63 (2002) 0563 10) performed their experiments. We propose an interpretation of the observed unexpected temperature oscillations at the convection onset in terms of coupled hot and cold piston effects. We have also considered the stability of two layers (hot and cold) of a same supercritical fluid in an unstable configuration. The first results show an analogy between the diffusion of species (Rayleigh-Taylor like instability) and thermal diffusion considered in this study. (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.