Development of a coupled DSMC - Particle photon Monte Carlo method for simulating atomic radiation in hypersonic reentry flows

With a fast reentry speed, the Stardust vehicle generates a strong shock region ahead of its blunt body with a temperature above 60,000 K. These extreme Mach number flows are sufficiently energetic to initiate gas ionization processes and thermal and chemical ablation processes. The generated charged particles affect nonequilibrium atomic and molecular energy distributions and shock layer radiation. In this work, we present the first loosely coupled direct simulation Monte Carlo (DSMC) simulations with the particle-based photon Monte Carlo (p-PMC) method to simulate Stardust reentry flows in the transitional flow regime. Eleven species including 5 ionization processes were modeled in DSMC, and the average ion velocity model was used to simulate electron motion. at these altitudes, the degree of ionization is predicted to be between 3 - 7 % along the stagnation line, and the maximum translational and electron temperatures are approximately 60,000 K and 20,000 K, respectively. to efficiently capture high nonequilibrium effects, emission and absorption cross section databases using the Nonequilibrium Air Radiation (NEQAIR) were generated, and N and O radiation was calculated by the p-PMC method. It was found that the N emission is approximately one order of magnitude higher than the O emission along the stagnation line due to the higher concentration of N at this altitude. The radiation energy change calculated by the p-PMC method has been coupled in the DSMC calculations. It was found that while the N and O atomic radiation does not have impact on the flow field at 81 km, at 68.9 km, the stronger radiation affected the flow field. The radiation resulted in lowering the gas temperatures in the high emission region, but slight increase of temperatures near the body as well as convective heat flux to the Stardust surface.