Ionization Nonequilibrium in Expanding Flows

Approximate methods are developed for solving the electron-ion kinetic equations in expanding quasi onedimensional airflows. Results arc obtained for inviscid nozzle flows at conditions appropriate to shock tunnel testing and are compared with exact numerical solutions. Effects on r-f transmission and d-c conductivity are examined. Since two-body deionization never fully freezes in the flows considered, the assurnption of sudden freezing gives an upper bound on the residual ionization at large area ratios. The use of an asymptotic form of solution with the freezing criterion provides an improved estimate for such cases. Ionization nonequilibrium is also considered for the plasma sheath associated with blunt hypersonic bodies flying at high altitudes. The influence of atomic ions is examined for typical re-entry conditions. (auth)