Heat Transfer and Diffusion in a Non-equilibrium Boundary Layer

Close to the surface of a hypersonic space vehicle reentering the Earth atmosphere, strongly non-equilibrium conditions are established.While crossing the bow shock, the gas is substantially compressed and heated. Due to the high temperature in the flow, the dissociation rate increases and strong vibrational excitation occurs. In the vicinity of the cold surface, the temperature of translational and rotational degrees of freedom drops sharply, and the vibrational temperature appears to be higher than that of the gas. Under such conditions, the distribution of molecules over the vibrational levels significantly differs from equilibrium, dissociation near the high-temperature external edge of the boundary layer as well as recombination near the cold surface are substantially non-equilibrium, which, in turn, results in the formation of the non-Boltzmann vibrational distributions. These strongly non-equilibrium distributions may noticeably affect the transport processes.