Analysis of the FIRE II flight experiment by means of a collisional radiative model

An accurate investigation of the behavior of electronically excited states of atoms and molecules in the post shock relaxation area is carried out by means of the Collisional-radiative model. The model is applied to a 1D shock tube code and the operating conditions are taken from three points in the trajectory of the FIRE II flight experiment. We account for thermal nonequilibrium between the translational and vibrational energy modes of individual molecular species and treat the electronic states of atoms and molecules as separate species. Relaxation of free-electrons is also accounted for by making use of a separate conservation equation for their energy. Non-Boltzmann distributions of the electronic state populations of atoms and molecules are allowed. Deviations from Boltzmann distributions are expected to occur in a rapidly ionizing regime behind a strong shock wave, due to the depletion of the high lying bound electronic states. In order to quantify the extent of departure from equilibrium of the electronic state populations, results are compared with those obtained assuming a Boltzmann distribution.