Investigation of the effects of electron translational nonequilibrium on numerical predictions of hypersonic flow fields

In the present study, flight regimes of hypersonic vehicles are identified in which the lack of thermal equilibrium between the vibrational-electronic and the electron translational energy modes plays an important role in the determination of the flow field character. The effect of the nonequilibrium of the electron translational and vibrational-electronic modes on the flow field parameters of interest such as plasma density, electron temperature, and radiative heat flux is quantified. Additionally, the importance of the selection of the controlling temperature when modeling the ionization source terms in the flow field equations is investigated. The RAM-C II and Stardust vehicles and their associated missions are used as test cases. At the flight conditions investigated in this study, it appears that significant differences in the prediction of electron number density and temperature exist mainly for the lower energy, RAM-C II flight conditions. At the higher energy Stardust flight conditions, the differences in both the electron properties and the predicted radiation spectra are generally small between the electron equilibrium and nonequilibrium simulation results. The results of this study indicate that the selection of controlling temperature is important when modeling the associative ionization and reverse dissociative recombination reactions at these flight conditions.