Molecular dynamics simulations of normal shock waves in dilute gas mixtures

The structure of a normal shock waves in dilute gas mixtures of various compositions (Xenon-Helium and Argon-Helium) are studied using Molecular Dynamics (MD) and Direct Simulation Monte Carlo (DSMC). The MD solutions reproduce well the experimental data, with the exception of the parallel temperature profile in the 24.7% Ar-He mixture, despite the satisfactory agreement between the parallel velocity profiles. The Generalized Hard Sphere (GHS) DSMC solutions match almost perfectly the MD data, for all the cases considered. Using textbook parameters for like particles and their arithmetic averages for unlike particles, the Variable Hard Sphere (VHS) model fails to describe the shock wave structure in the Xe-He mixture. For the Ar-He cases, the VHS diffusion cross-section better approximates that obtained with the Lennard-Jones potential. Therefore, the VHS DSMC solutions exhibit less significant differences with those obtained with MD. If the VHS model is properly parametrized, the agreement between DSMC and MD solutions increases significantly. These cases exemplify situations where MD simulations based on a reliable interatomic potential can be used to inform simplified collision schemes used in DSMC.