Rovibrational internal energy excitation and dissociation of molecular nitrogen in hypersonic flows

A rovibrational collisional model is developed to study the internal energy excitation and dissociation processes behind a strong shockwave in a nitrogen flow. The reaction rate coefficients are obtained from the ab initio database of NASA Ames Research Center. The master equation is coupled with a one-dimensional flow solver. The system of equations is solved for conditions expected for reentry into Earth's atmosphere at 10 km/s. In addition, coarse graining models have also been proposed by lumping the rovibrational energy levels into a smaller number of bins. The results obtained by means of the full CR model and a coarse graining model based on a uniform distribution of the levels within a bin are compared to those obtained by means of a standard multitemperature model and a vibrational CR model. Thermalization and dissociation occurs after a larger distance for the full CR model compared to the distance predicted by both the multitemperature model and vibrational CR model. The uniform distribution bin model allow to describe accurately the internal energy relaxation and dissociation processes based on a reduced number of equations.