Investigation of Nonequilibrium Effects in Axisymmetric Nozzle and Blunt Body Nitrogen Flows by means of a Reduced Rovibrational Collisional Model

摘要

A vibrational collisional model is proposed to study the internal energy excitation and dissociation processes in 2D axisymmetric nonequilibrium nitrogen flows. The chemical database for the N + N_2 system recently developed at NASA Ames Research Center provides rate coefficients for rovibrational dissociation and excitation. Vibrationally averaged rate coefficients for N + N_2 inelastic collisions are computed based on the hypothesis of equilibrium between translational and rotational modes. Inelastic N_2 + N_2 collisions are also considered based on literature data. The governing equations for 2D inviscid axisymmetric nonequilibrium flows are discretized in space by means of the finite volume method. Time integration is performed through the use of the operator splitting approach. Applications to the supersonic flow through the converging-diverging nozzle of the NASA Ames EAST (Electric Arc Shock Tube) facility and to the flow over a sphere, show that populations of vibrational levels experience departure from a Boltzmann distribution. For the nozzle case, experimental data are available and have been compared against computational results. A good agreement between the two is observed.