Rayleigh and parametric thermo-vibrational instabilities in supercritical fluids under weightlessness

Under the absence of gravity forces, the interaction of vibration with a thermal boundary layer (TBL) can lead to a rich variety of dynamics in a supercritical fluid (SCF). When subjected to vibration, a SCF can display different kinds of instabilities for different relative directions of the TBL and vibration. Rayleigh vibrational instability is formed when the vibration direction is tangential to the TBL. When the direction of vibration is perpendicular to the TBL, instabilities of parametric nature can develop. Two-dimensional finite volume numerical analysis of supercritical H2 filled in a square cell under vibration is carried out. The vibrational amplitudes range from 0.05 to 5 times the side of the cell and frequencies vary between 2.78 Hz and 25 Hz. Three different thermal boundary conditions (isothermal walls, adiabatic vertical/isothermal horizontal walls, and adiabatic horizontal/isothermal vertical walls) have been considered with various temperature proximities to the critical point (10 mK, 1...