Vibrational state to state kinetics in expanding and compressing nitrogen flows

The analysis of the behavior of a nitrogen plasma undergoing expansion in a nozzle and compression in the zone behind a normal shock wave is studied using a vibrational state-to-state collisional model developed from the data NASA Ames Database quantum chemist group calculations based on QCT (quasi-classical- trajectory) method. In this way non-Boltzmann distributions of vibrational states of molecular nitrogen are allowed. Departures from that are shown to occur in the divergent portion of a supersonic nozzle and behind a strong normal shock, where characteristic times for collisional interactions to occur become comparable with flow macroscopic time scale. This aspect is of crucial importance if a correct estimation of surface heat flux experienced by a vehicle entering a planetary atmosphere is wished or when experimental data acquired in high enthalpy wind tunnels equipped with a supersonic nozzle must be related to real flight conditions. Both inviscid and viscous computations are considered and a comparison against multi-temperature approach results is performed. The analysis is simplified by assuming for both cases 1D flow (quasi 1D for nozzle) because of the high number of governing equations. Numerical solutions to them are obtained by means of Finite Volume Method with implicit or semi-implicit time discretization.