Computation of rarefied gas flows around a NACA 0012 airfoil

Rarefied gas flows around a NACA 0012 airfoil with the speed varying from supersonic to low subsonic are simulated using particle and continuum approaches. Some crucial issues such as serious’statistical scatter encountered in DSMC calculation of the low subsonic flow, prediction of continuum breakdown, and outer boundary conditions for the transonic and-subsonic flows, are addressed. The simulated density and velocity flowfields are in agreement with experimental data. A criterion of continuum breakdown based on the Chapman-Enskog theory indicates that the kinetic foundation of the Navier-Stokes equations is invalid both at the-bow shock and in a large region around the airfoil for supersonic flows, in the region adjacent to the body surface for transonic flow, and in the thin Knudsen layer for low subsonic flow.