Modeling of Rarefied and Weakly Ionized Hypersonic Flows Using the Direct Simulation Monte Carlo Method

During atmospheric entry, a plasma layer with ions and electrons forms around the vehicle surfaces, evident from the radio communication blackout. In this paper, the direct simulation Monte Carlo method is used to model the plasma formation in rarefied and weakly ionized hypersonic flow. The first objective is to implement and numerically verify existing high-temperature chemical kinetic models in the recently developed direct simulation Monte Carlo / particle-in-cell code, Comet. This code works on either the CPU or GPU devices, and uses a distributed unstructured mesh. It achieves large-scale parallel computing and is able to handle complex simulation geometry. The second objective is to numerically investigate the plasma formation of a canonical hypersonic vehicle geometry at representative Earth entry flight conditions, which used the two-dimensional hypersonic flow over a circular cylinder geometry at 81 km altitude. It can serve as a common test case for future chemical kinetic model comparisons between different computational codes. The third objective is to assess and validate numerical methods and chemical kinetic models in Comet. Simulation results at conditions corresponding to the RAM C-II hypersonic flight experiment are presented. Good agreement is observed between the simulated and measured electron number density.