Prediction of Nonequilibrium Air Plasma Radiation Behind a Shock Wave

The absolute radiation measurements obtained in the electric arc-driven shock-tube facility at NASA Ames Research Center were analyzed to test the collisional-radiative model developed at Ecole Centrale Paris. Two conditions representative of Earth reentry at 10.54 and 11.17km/s were investigated in the vacuum ultraviolet and infrared spectral ranges. For each of the conditions, the corresponding charge-coupled device images were analyzed. The electron number density was inferred from Stark-broadened nitrogen and H lines. Comparisons with the predicted electron number density profiles enabled us to validate the ionization rate constant model implemented in the flowfield solver and to accurately locate the shock front. For both freestream conditions and all the spectral ranges, the predictions of the initial intensity rises were improved when the total spatial smearing (due to the shock motion, the optics, and the camera) was taken into account. The nonequilibrium intensities observed in the vacuum ultraviolet and infrared spectral ranges were underpredicted by the collisional-radiative model when only electron-impact excitation and ionization processes were taken into account. Then, the effect of heavy-particle impact processes was studied by applying various multitemperature dissociation rate constant and vibration-dissociation coupling models as well as heavy-particle impact excitation models. The nonequilibrium peak intensities observed in the vacuum ultraviolet and infrared spectral ranges were shown to be controlled by heavy-particle impact excitation processes.