QCT-based vibrational collisional models applied to nonequilibrium nozzle flows

Thermal and chemical nonequilibrium effects are investigated in hypersonic nozzle expanding flows by means of vibrational collisional models. The rate coefficients for rovibrational dissociation and excitation are provided by two chemical databases for the N+N₂ system recently developed at NASA Ames Research Center and the University of Bari. Vibrationally averaged rate coefficients for N + N₂ collisions are computed based on the hypothesis of equilibrium between translational and rotational modes. N2+N ₂ collisions are also considered based on literature data. Inviscid and quasi 1D governing equations are discretized in space by means of a finite volume method. A fully implicit time integration method is applied to obtain steady state solutions. Results show that, for both N + N₂ and N ₂ + N₂ collision dominated flows, the populations of vibrational levels deviate from a Boltzmann distribution. An accurate investigation of vibrational level dynamics shows the different behavior of low and high-lying states. Comparison against experimental data acquired at the EAST facility of NASA Ames Research Center demonstrate good agreement between the computed and experimental results.