Molecular collision models on aerodynamic separation of gas mixtures based on direct simulation Monte Carlo method

The selection of the molecular collision model is essential for accurately predicting aerodynamic separation characteristics in the numerical simulation of rarefied gas flows. The aerodynamic separation characteristics of He and Ne gas mixtures under various Knudsen numbers (0.06–10) and equilibrium temperatures (10–1500 K) are investigated using the direct simulation Monte Carlo method in combination with ab initio potential model based on quantum scattering and the classical variable soft sphere (VSS) scattering model. The distributions of mole fraction, separation efficiency, Mach number, temperature, and pressure are analyzed. In the free molecular regime, the ab initio potential and VSS models produce nearly identical results, exhibiting low separation efficiency and minimal sensitivity to temperature. In the transitional and slip flow regimes, separation efficiency increases with equilibrium temperature, and an optimal Knudsen number exists at which the pressure and temperature differences between He and Ne are maximized, yielding the most effective separation. At low temperatures (especially T<100 K), significant differences appear between the ab initio potential and VSS models, with the maximum relative deviations in Ne mole fraction and separation factor reaching 7.7% and 11.2%, respectively, and the maximum deviations in Mach number, temperature, and pressure reaching 10.4%, 14%, and 14%. Compared to the VSS model, the ab initio potential more accurately captures quantum scattering effects under low-temperature conditions, improving the prediction of mixture separation.