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.

The accurate prediction of the aeroheating performance of hypersonic vehicles requires more detailed modeling of the catalysis process, rather than merely employing a catalytic coefficient. In this paper, the theoretical modeling, as well as the direct simulation Monte Carlo method, is used to preliminarily study the incomplete chemical energy accommodation effects, that is, only a part of the potential energy released in the heterogenous recombination reaction is transferred to the surface, while the remaining is retained as the vibrational energy of the desorbed molecule. An integrated model is proposed to describe the contribution of each energy mode in the rarefied nonequilibrium heat and mass transfer process. Based on the model and several Damköhler numbers, an analytical formula is derived, and is also shown to compare well with the numerical results. On account of the incomplete accommodations of the chemical and vibrational energy on the wall, a variation up to 20% is observed in predicting the stagnation point heat flux under typical nonequilibrium flow conditions. This study could enrich our understanding of the nonequilibrium heat transfer phenomenon and also shows a potential practical value.