Combined Effects of Thermal Non-equilibrium and Chemical Reactions on Hypersonic Air Flows Around An Orbital Reentry Vehicle

The present work computationally investigated the combined effects of thermal non-equilibrium and chemical reactions on hypersonic air flows around an orbital reentry vehicle during its reentry. The chemically reacting gas flow around the orbital vehicle was simulated for actual reentry trajectories, with a computational solver based on the Navier–Stokes–Fourier equations. Hypersonic flows for a wide range of flying altitudes from 40 to 80 km were examined. We first analyzed important properties such as Mach number, trans-rotational temperature, vibrational temperature, chemical species composition, and surface properties such as the maximum heat flux for various altitudes. We then investigated the distribution of heat flux on the surface of the orbital reentry vehicle and the coupled effects of thermal non-equilibrium and chemical reactions on the hypersonic air flows. The computed heat flux results were compared with actual flight test data obtained during reentry of the orbital vehicle. The computed results were found to be in excellent agreement with the flight test data until an altitude of 60 km. Finally, we propose an explanation why heat flux was over-predicted around 70 km altitude but returned to better agreement at the higher altitude of 80 km. The phenomenon is based on two competing effects: the shortcoming of the first-order law of heat flux in the NSF equations and the inaccurate description of the effects of thermal non-equilibrium on chemical reactions in Park’s two temperature model.