Boutrouft, Keltoum (2006) Rayleigh-Taylor like thermal instabilities in supercritical fluids. PhD thesis Mécanique, ENSAM 2006ENAM0067.

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Abstract

A numerical study of the stability in a two-layer system filled with a single pure supercritical fluid subjected to an initial temperature difference is performed. The very large compressibility and the very low heat diffusivity of near-critical fluids lead to a Rayleigh-Taylor like gravitational instability of the heat diffusion layer. This instability is similar to the one of two miscible fluids where molecular species diffusion coefficient is replaced by the heat diffusion coefficient. Our numerical results are consistent with respect to the dispersion relation derived by Duff et al. [Duff62] for a system of two miscible fluids (argon-bromine mixture falling into helium or air). We have also shown that when the thickness of the lower layer becomes smaller than the heat diffusion length based on the maximum growth rate, the system is stable. A linear stability diagram has been established as a function of three parameters: the thickness of the lower layer, the density difference between the two layers and the distance to the critical point. When the critical point is approached, the high initial stratification (due to the high compressibility) of this Rayleigh-Taylor-like configuration has seen the effect of stabilising the system. We have also shown that the acoustic filtering procedure is not needed to reduce the computational time due to the weak formulation of finite volume method (filtering with the integral form of the equations).

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