Applicability of 5, 7, and 11 Species Air Models in Nonequilibrium Hypersonic Reacting Flows

摘要

The applicability of 5, 7, and 11 species air models to predict gas and surface properties at nonequilibrium hypersonic conditions is examined for a sphere-cone geometry. The direct simulation Monte Carlo method is used in the computations, and the model validation is conducted for a RAM-C configuration at 61 km and 71 km, and a free stream velocity of 7.6 km/s. A RAM-C forebody is then used to examine the impact of free stream conditions, with the free stream velocity varying from 6 to 9 km/s, and Knudsen number, from 0.0003 to 0.0012. Ionization is shown to noticeably change flow properties immediately behind the shock at a velocity of 9 km/s, and in the boundary layer, for velocities of 8 km/s and higher. The 7 species model is generally applicable up to 8 km/s. For 9 km/s, it differs significantly from 11 species model, especially inside the boundary layer, and underpredicts the heat flux reduction due to ionization by almost a factor of two. Compared to the 5 species model, the maximum reduction in the heat flux, observed at velocities over 8 km/s, is less than 3% for the 7 species model, and over 4% for the 11 species model.