STRUCTURE OF SHOCK WAVES WITH NONEQUILIBRIUM RADIATION AND IONIZATION

The investigations of this study are concerned with: (1) the physical processes that occur in the precursor and in the nonequilibrium region behind a strong shock wave during its approach to equilibrium in an argonlike gas; (2) the influence of different atom-atom collisional rates in the relaxation region on the precursor; and (3) the cause of precursor ionization, which in this study has been assumed to be the photoionization of both the ground and excited states. The argonlike gas is regarded as a combination of two gases; one consisting of electrons and the other of atoms and ions. Temperature differences between the two gases affect both the approach to equilibrium behind the shock wave and the precursor. Just behind the shock wave, the electron gas is cold relative to the atom gas. Farther into the relaxation region, the electron temperature approaches that of the atom gas, and thermal equilibrium is reached. Shortly thereafter, ionizational equilibrium is reached, and the gas begins to cool by the emission of excited-state radiation until it reaches its final steady state. The precursor ionization depends directly on the ratio of radiative to convective energy; thus, decreasing the ambient pressure increases both the extent and magnitude of the precursor. Increasing the atom-atom cross section increases the precursor ionization; however, changing the atom-atom cross section does not affect the extent of the precursor.