Chemical nonequilibrium effects in hypersonic pure air wakes

Abstract

Abstract : The effect of finite chemical reaction rates on the chemical structure of hypersonic wakes is examined. The technique of incipient nonequilibrium coefficients, based on linearized chemical kinetics for a 7-component (O2, N2, O, N, NO, NO+, e-) 10-reaction model of high temperature air, is utilized in the analysis. The far wake is treated as an asymptotic region; the near wake theory considers the viscous mixing of the boundary layer flow with the inviscid and recirculating flows in the base region, and the subsequent development of this viscous core into the wake region downstream. A range of altitudes and flight speeds of practical interest is considered. The results show where non-equilibrium effects are important in the wake and whether they arise primarily from convective or diffusive effects. The species that are the principal contributors to the non-equilibrium effects are also identified. The incipient non-equilibrium results are then related to calculations assuming chemically frozen flow. By the application of chemical kinetics to the frozen results, it can be shown that the appearance of incipient non-equilibrium effect bears an inverse relationship to the validity of the frozen flow assumption for equivalent wake calculations. (Author)