Numerical Study of Nonequilibrium Airflow over a Sphere-Cone with State-to-State Model

The thermochemical nonequilibrium airflow over a sphere-cone flying at 4230 m/s is investigated by the state-to-state (StS) model. Five chemical species ([Formula: see text], [Formula: see text], NO, N, O) and each vibrational state are considered, leading to a 157-pseudospecies gas mixture. Fully implicit treatment of the thermochemical source term and parallel computation are employed. The prediction of wall heat flux agrees well with the flight data. The results of vibrational distribution show an evident deviation from Boltzmann distribution at vibrational temperatures. In the region of vibrational excitation behind the shock wave, the vibrational distribution tails exhibit a significant overpopulation. In the dissociation region further downstream of the nose shock wave, an underpopulation of high-lying levels occurs. In the region with thermochemical freezing caused by rapid flow expansion, the vibrational temperature of [Formula: see text] exceeds the translational temperature while the vibrational temperatures of NO and [Formula: see text] are close to the translational temperature, the high-lying levels of all molecules are overpopulated, and the vibrational distribution of [Formula: see text] forms a plateau around the intermediate levels. The wall catalysis influences the evolution of the vibrational distribution within the boundary layer. Effects of vibrational excitation of NO and multiquantum vibrational–translational transitions by molecular collisions are evaluated.