Numerical Study And Application About The Model Of Gas-solid Interaction With Large Temperature Difference

The gas-solid interaction is the basis of many physical problems,and the scattering kernel that describes the distribution of the reflection velocity of gas molecules is important.The classical scattering kernel models have free parameters without considering the influence of the gas-solid temperature difference.With the deepening of the research on micro-scale flow and hypersonic flow in the rarefied environment,higher requirements are put forward for the gas-solid interaction model.This paper directly simulates the gas-solid interaction process from the molecular scale,and then reconstructs the scattering kernel to investigate the influence of the gas-solid temperature difference,expands the scope of the application of the gas-solid interaction model,and applies it to the simulation of high-speed rare gas flow.Firstly,using the GPU dual-layer parallel molecular dynamics(MD)method,the scattering of gas with different temperatures on solid surface with specified temperature is directly simulated and the relationship between the reflection velocity of the gas molecules and the incident state is obtained.Furthermore,based on the Cercignani-Lampis-Lord(CLL)model,a more accurate modified scattering kernel with the effect of the gas-solid temperature difference is reconstructed from the MD simulation data using the machine learning method.The dependency of parameters in scattering kernel on the gas-solid temperature ratio and the scattering characteristics of gas molecules are analyzed.The results show that within the temperature range discussed,compared with the MD simulation results.The characteristic temperature in the modified kernel is the gas temperature,instead of the wall temperature which is used in traditional kernels.And the adjustment coefficients depend on both the incident velocity and gas-solid temperature ratio.The larger the gas-solid temperature ratio,the stronger the influence of the molecular incidence velocity on the scattering characteristic.When the temperature ratio is larger than 2.5,the probability density of reflection velocity in tangential direction almost keeps constant but that in normal direction still changes slowly with the temperature.Secondly,the hypersonic rarefied gas flow around the oblique split is calculated by the direct simulation Monte Carlo(DSMC)method,and the effects of different scattering kernels are analyzed.The calculation results of the standard CLL model considering the high temperature non-equilibrium effect of real air show that the value of the adjustment coefficients basically don't change the flow structure,but the shock angle increases slightly with the increase of the tangential momentum adjustment coefficient,the wall slip velocity decreases,and the vibration temperature near the wall increases significantly.Furthermore,the effects of Maxwell model,standard CLL model and the Modified CLL(MCLL)model on the hypersonic flow of monoatomic gas around oblique wedge are investigated,in which the adjustment coefficients of the standard CLL model are determined by MD data.The differences of the flow result calculated by different models still exist mainly near the wall.Compared with the results of the MCLL model,the results of Maxwell model vary in a larger range with the adjustment coefficient,and the smaller the adjustment coefficient is,the more obvious the difference is;the CLL model is basically consistent in pressure distribution,slip velocity and wall heat flux,but the temperature near the wall is obviously lower.This shows that the MCLL model considering the local gas-solid temperature difference can more accurately describe the wall effect in hypersonic flow.