Gas-surface interaction features under effects of gas-gas molecules interaction in high-speed flows

Abstract

Understanding interactions between gas molecules and solid surface is key to the aerodynamic design of high-speed, high-altitude aerospace vehicles, but there is a large dispersion of gas-surface interaction parameters or namely accommodation coefficients. The uncertainty results partly from different considerations of the interaction between gas molecules in various experimental and numerical methods. In this study, effects of gas-gas molecules interaction are systematically discussed by comparing two different approaches of molecular dynamics simulation of high-speed argon molecules scattering on a graphite surface. The popularly-used “single scattering” approach repeats the scattering process of a single gas molecule without considering the gas-gas molecules interaction. The newly-developed “continual scattering” approach continually shoots gas molecules at the surface, considering collisions between gas molecules in addition to gas molecules’ collisions with surface. Gas-surface interaction features in the two approaches are compared and discussed under various affecting factors including rarefaction degree, gas-surface interaction strength, surface temperature and incident velocity. It is shown that these two approaches usually produce different accommodation coefficients, and the corresponding mechanisms are explained. This study could help clarify some doubts about the selection of accommodation coefficients in engineering practice, and also provide an instruction on design of an appropriate molecular dynamics simulation approach.