Nonequilibrium Expansions of Air with Coupled Chemical Reactions

Abstract

Analysis and solutions of the streamtube gas dynamics involving coupled chemical rate equations are carried out. Results are presented for airflows along the surface of blunt bodies and through hypersonic nozzles. Speeds and altitudes corresponding to re‐entry were selected to obtain initial conditions for the external flow calculations. Conditions appropriate to hypersonic tunnel testing were chosen for the nozzle flow calculations. Composition histories are shown for a kinetic mechanism including 6 species and 14 reactions. Gas‐dynamic effects of nonequilibrium processes qualitatively resemble those reported earlier. However, the freezing process is complicated by the coupling of the nitric oxide shuffle reactions with the dissociation‐recombination reactions. In many cases of hypersonic nozzle flows where the energy in nitrogen dissociation is significant, the fast shuffle reactions prevent nitrogen‐atom freezing which would otherwise occur if three‐body recombination were the only process operating. Nitric oxide concentrations undershoot the equilibrium values if the ratio of nitric oxide to oxygen molecule concentrations exceeds unity in the freezing region. This depletion of nitric oxide leads to nitrogen‐atom freezing.