Impact of the Ionization Reaction Set in Nonequilibrium Hypersonic Air Flows

Abstract

The impact of the gas-phase ionization on flow and surface properties at nonequilibrium hypersonic conditions is examined with the direct simulation Monte Carlo method for five-, seven-, and 11-species air models. The freestream velocity is varied from 6 to $9\mathrm{km}/\mathrm{s}$ , and the Knudsen number is varied from 0.0003 to 0.0012. Validation is conducted for a normal shock wave and Radio Attenuation Measurement C Band (RAM-C) sphere–cone configuration. The model analysis is performed for a RAM-C forebody. Ionization is shown to noticeably change flow properties inside the shock at velocities of $9\mathrm{km}/\mathrm{s}$ and higher, as well as in the boundary layer at velocities of $8\mathrm{km}/\mathrm{s}$ and higher. The seven-species model is generally applicable up to $8\mathrm{km}/\mathrm{s}$ . For higher velocities, it differs significantly from the 11-species model, especially inside the boundary layer; and it underpredicts the heat flux reduction due to ionization by a factor of two. Compared to the five-species model, the maximum change in the heat flux is 2% for the seven-species model and 4% for the 11-species model.