NUMERICAL SIMULATION OF NON-EQUILIBRIUM FLOW-RADIATION CHARACTERISTICS AT HYPERSONIC SPEEDS

The convective and radiative heating to which a hypersonic vehicle is subjected during hypersonic flight may be of comparable order of magnitude, so reasonably accurate prediction of aerodynamic heating requires a combination of both. In this paper, a high temperature air collisional-radiative model with non-Boltzmann electronical energy levels and vibrational energy levels distribution is developed, and coupled with the one-dimensional post-shock flow equations to calculate the non-equilibrium flow characteristics behind the shock front. The non-equilibrium radiation property, radiation intensity and radiation transfer of the post-shock flow are calculated by using the line-by-line radiation transfer model, which considers the bound-bound, bound-free, free-free radiative mechanisms of atoms and molecules in detail. The effects of flight altitudes and Mach numbers on non-equilibrium flow and radiation transfer process are deeply analyzed. The calculative results indicate that there are significant thermal non-equilibrium effect, chemical non-equilibrium effect and energy levels non-equilibrium effect existed in the post-shock flow for the high altitude and high Mach flight, and there are obvious under-population of the high vibrational energy levels and the high-lying electronical excited states in the near shock region, which are respectively caused by the rapid dissociation reaction of high vibrational states and the ionization processes of high-lying electronical states. Under the high altitude and high Mach conditions, the vacuum ultraviolet radiation is main contributor of radiative transfer process, which is mainly caused by the high energy atomic bound-bound radiative transition processes. With the decrease of altitude and Mach number, the degree of gas dissociation and ionization in the shock layer decreases, leading to the corresponding decrease of atomic radiative emission. Meanwhile, the number density of molecules increases and the contribution of molecular radiation increases, which leads to the enhancement of radiation transfer in infrared, visible and ultraviolet spectral bands, and the weakening of vacuum ultraviolet radiation transfer process.