Published online by Cambridge University Press: 13 March 2009
A unified picture of the structure of steady, one-dimensional shock waves in partially ionized argon, in the absence of external electric or magnetic field, is presented. The investigation is based on a two-temperature, three-fluid continuum approach, using the Navier–Stokes equations as a model and including non-equilibrium ionization. Quasi charge neutrality and zero velocity slip are assumed. The analysis of the governing equations is based on the method of matched asymptotic expansions and results in the following three layers: (1) a broad thermal layer dominated by electron thermal conduction, (2) an atom-ion (A-I) shock structured by the heavy particle (atoms and ions) collisional dissipative mechanisms and (3) an ionization relaxation layer (IRL) wherein electron- atom inelastic collisions dominate. Solutions have been obtained for the first two orders with respect to a small parameter, which is the ratio of energy fluxes due to heavy particle viscous dissipation and electron thermal conduction. Whereas only electron temperature and electric potential show any marked variation in the thermal layer, the changes in all the variables in both the A-I shock and the IRL are significant.
Inclusion of electron thermal conduction terms in the governing equations has been observed to introduce numerical instabilities in the analysis of the IRL. They are circumvented by adopting a regular perturbation scheme with respect to a local small parameter, which has been identified to be the ratio of the freestream degree of ionization to the nondimensional characteristic temperature for first ionization. Numerical results show that the effect of electron thermal conduction on the IRL profiles is significant. Results in the form of tables and figures are presented for five sets of equilibrium free-stream conditions.