Progress and future prospects for particle-based simulation of hypersonic flow

The direct simulation Monte Carlo method (DSMC) has evolved over 50 years into a powerful numerical technique for the computation of thermochemcial nonequilibrium gas flows. In this context, nonequilibrium means that velocity and internal energy distribution functions are not in equilibrium forms due to a low number of intermolecular collisions within a fluid element. In hypersonic flow, nonequilibrium conditions occur at high altitude and in regions of flow fields with small length scales. This article highlights significant developments in particle simulation methods (since 2001) applied specifically to hypersonic flows, which now includes Molecular Dynamics in addition to DSMC. Experimental measurements that have led directly to improved DSMC models will be highlighted. Al- gorithm development for DSMC aimed at increasing computational effciency is discussed with a focus on hybrid particle-continuum methods. New research that applies all-atom Molecular Dynamics simulation and trajectory-based DSMC simulation to normal shock waves is summarized. Finally, a discussion of state-resolved DSMC modeling is included with reference to future prospects for particle simulation methods and in particular for the DSMC method.