Molecular Dynamics Simulations of High Speed Rarefied Gas Flows

To understand the molecular behaviour of gases in high speed rarefied conditions, we perform molecular dynamics (MD) numerical experiments using the open source code OpenFOAM. We use shear-driven Couette flows as test cases, where the two parallel plates are moving with a speed of U-w in opposite directions with their temperatures set to T-w. The gas rarefaction conditions vary from slip to transition, and compressibility conditions vary from low speed isothermal to hypersonic flow regimes, i.e. Knudsen number (Kn) from 0.01 to 1 and Mach number (Ma) from 0.05 to 10. We measure the molecular velocity distribution functions, the spatial variation of gas mean free path profiles and other macroscopic properties. Our MD results convey that flow properties in the near-wall non-equilibrium region do not merely depend on Kn, but they are also significantly affected by Ma. These results may yield new insight into diffusive transport in rarefied gases at high speeds.