The stability analysis of two layers in a supercritical pure fluid: Rayleigh–Taylor-like instabilities

Abstract

We numerically investigate the linear stability of two superposed near critical isobar fluid layers of variable thickness initially at two different temperatures. The very large compressibility and the very low heat diffusivity of near critical pure fluids induce very large density gradients which lead to a Rayleigh–Taylor-like (RTL) gravitational instability of the heat diffusion layer when the top layer temperature is some mK cooler than the bottom one. This instability in a one-phase fluid seems to be similar to that which occurs in between two miscible liquids where the species diffusion is replaced by the heat diffusion coefficient. We find that this RTL configuration becomes stable when the heat diffusion length on the time scale of the faster unstable mode becomes larger than the bottom hot layer thickness.