Influence of Gas-Surface and Gas-Gas interactions on the energy accommodation coefficient in non-equilibrium hypersonic gas flows

Abstract

Accurate accommodation coefficients are crucial in predicting aerodynamic force and heating in hypersonic rarefied flows. This study employs molecular dynamics simulations to investigate the characteristics of non-equilibrium hypersonic flow and its impact on the energy accommodation coefficient (EAC). Our findings reveal that the non-equilibrium gas flow in the gas-surface interaction region comprises an equilibrium subsonic flow, an incident hypersonic flow, and its reflected counterpart. Gas-surface and gas–gas interactions occur simultaneously as gas atoms incident toward the solid surface, with the latter enhancing the EAC by altering the ratios of collision types. Overall, an increase in the ratios of trapping-desorption and permanent-adsorption collisions enhances the EAC at the interface. Results indicate that the number density of the subsonic flow determines the transition from immediate-reflection collisions to trapping-desorption collisions, while the ratio between the potential well depth and the internal energy of the subsonic flow determines the occurrence of permanent-adsorption collisions. These findings disclose the influence of the gas-surface and gas–gas interactions on the atomic collision types and EAC in a hypersonic flying interface, providing valuable insights for predicting the aerodynamic heating in rarefied gas flow.