DIRECT-SIMULATION MONTE CARLO MODELING ON TWO-DIMENSIONAL RAYLEIGH-BÉNARD INSTABILITIES OF RAREFIED GAS

This study investigates numerically the convective instabilities of rarefied gas in two-dimensional enclosures by the direct-simulation Monte Carlo (DSMC) method. A simulation using an enclosure with length-to-height aspect ratio AS = 2.016 is conducted to validate the value of the critical Rayleigh number on the onset of convection. Enclosures of AS = 2 and 4 are chosen to explore the influences of the Knudsen number Kn and initial wall temperatures on the flow. The results indicate that the different initial conditions may cause multiple solutions for the convection rolls and the Boussinesq approximation is no longer valid for rarefied gases of high Kn.