Nonequilibrium structure of argon shock waves

Abstract

This theoretical study investigates the influence of (1) the nonequilibrium excited state population in the relaxation region and (2) line radiation in the precursor on shock wave structure by considering strong shock waves propagating at Mach 18 and 24 into a theoretical argon-like gas at a pressure of 1 cm Hg and a temperature of 300 °K. The argon atom is modeled as having two bound states plus a continuum, and the calculations include finite atom-atom and electron-atom collisional ionization and excitation rates as well as continuum and line radiation. The electron gas is allowed to be at a different temperature from the atom gas; consequently, three types of of nonequilibrium exist: ionization, excitation, and thermal. In the collisional relaxation region, which serves as a source of radiation to create the precursor, the degrees of ionization and excitation generally lag behind their respective local equilibrium values. By doing so they greatly influence the emission of radiation. The line wing radiation increases the extent of the precursor compared with former studies which considered only continuum radiation. However, elimination of the assumption that the excited states are in equilibrium with the electrons at the electron temperature decreases the magnitude of the precursor compared with results where the assumption has been used because the radiative flux is reduced.