Abstract:The StS (state-to-state) model and MT(multi-temperature) model were used to numerically simulate and analyze the high-temperature air flow of 11 chemical species behind normal shock waves. The StS model resolved vibrational levels of neutral molecules and electronic levels of neutral atoms; the MT model distinguished the translational-rotational temperature, vibrational temperatures of neutral molecules, and the electron temperature. Simulation results for velocities ranging from 5 km/s to 11 km/s before the shock front demonstrate that immediately behind the shock wave, due to the dissociation and ionization reactions, the higher vibrational levels of molecules and the higher excited electronic levels of atoms are underpopulated relative to the Boltzmann distribution at the corresponding temperatures. Compared to the StS model, the MT model shows that the excitation of vibrational and electronic energies and the attainment of thermal equilibrium in different energy modes occur later, while chemical reactions also take place later but reach chemical equilibrium earlier. The MT model underpredicts vibrational energy loss from chemical reactions while overpredicting electronic energy loss due to electron-impact ionization. Moreover, obtained derived vibrational temperatures of molecules and electron temperature fail to accurately characterize the nonequilibrium population distributions of particle energy levels.