DSMC acceleration techniques applied to shock heated and recirculating flows

Direct simulation Monte Carlo (DSMC) calculations provide a suitable technique to study flows in the transition regime between continuum and free-molecular flow. However, DSMC becomes computationally expensive for near continuum flows because of three requirements; (1) cell sizes must be refined to the local mean free path (2) time steps must be smaller than the local mean collision time and (3) a sufficient number of simulation particles is required for statistical reasons. The current work investigates two acceleration techniques; namely the subcell method and the variable time step method, and evaluates the accuracy and efficiency of these methods through a parametric study of hypersonic flow over a cylinder geometry. Stagnation line temperature profiles, along with surface heat flux profiles, serve as the relevant macroscopic results to judge numerical convergence. In addition, converged DSMC results are presented for hypersonic flow over an expansion/compression geometry, referred to as the“tick” configuration. Specifically DSMC results for both non-reacting and reacting air flows are obtained for conditions matching ongoing experiments performed in a high-enthalpy wind tunnel facility.