Development of Coupled Particle Hypersonic Flowfield- Photon Monte Carlo Radiation Methods

Abstract

DOI: 10.2514/1.44645 With its fast reentry speed, the Stardust vehicle generated a strong shock region ahead of its blunt body with a translational temperature in excess of 60,000 K. Such an extreme Mach number flow is sufficiently energetic to initiate gas ionization processes and thermal and chemical ablation processes. The generated charged species affect nonequilibrium atomic and molecular energy distributions and shock layer radiation. In this work, we present the first loosely coupled direct simulation Monte Carlosimulations with the particle-based photon Monte Carlo method to simulate high-Mach-number reentry flows in the near-continuum to transitional flow regimes. Eleven species including five ionization processes were modeled in direct simulation Monte Carlo, and the average ion velocity model was used to simulate the electron motion. The degree of ionization is predicted to be between 3–7% along the stagnation line for altitudes of 68.9 and 81 km, and the maximum translational and electron temperatures are approximately 60,000 and 20,000 K, respectively. To efficiently capture the nonequilibrium radiation generated by this flow, emission and absorption coefficient databases using the Nonequilibrium Air Radiation computational tool were generated. However, in contrast to the Nonequilibrium Air Radiation computational tool, radiative transport was modeled by the particle-based photon Monte Carlo method instead of the simplified one-dimensional tangentslab approximation. It was found that the atomic nitrogen emission is approximately 1 order of magnitude higher than the atomic oxygen emission along the stagnation line due to the higher concentration of atomic nitrogen at this altitude.Theradiationenergychangecalculatedbytheparticle-basedphotonMonteCarlomethodwascoupledwith the direct simulation Monte Carlo calculations, and it was found that although the atomic nitrogen and atomic oxygenatomicradiationdoesnothaveanimportantimpactonthe flowfieldat81km,thestrongerradiationmodified the flowfield and heat flux at the wall at an altitude close to peak heating.