Thermoconvective instabilities of 2D Poiseuille-Rayleigh-Bénard for supercritical fluids in micro/macro-channels

International audienceThe objective of this paper is to study the influence of specific properties of supercritical fluid on the thermoconvective instabilities phenomena comparatively with those observed in the ideal gases case. This study concerns the mixed convection in a supercritical fluid flowing in a millimetric channel heated from below and traversed by a supercritical flow CO2 . The dependence of the instability threshold on the Reynolds and Prandtl numbers is investigated as well as the characteristics of the thermoconvective structures for a large range of the relevant dimensionless parameters. The study is carried out by direct numerical simulations based on the solution of the Navier-Stokes equations, coupled with the energy equation and the Peng-Robinson equation of state, in the framework of the low Mach number approximation. Simulations were performed for Reynolds numbers ranging from 12 up to 101. The instability threshold was determined from numerical solutions for several values of Re and it was found to vary as a fourth degree polynomial of Re