Computation of high-altitude hypersonic flow field radiation

Accurate calculations of radiation on and from transatmospheric flight vehicles are currently a challenge to computational aerodynamicists. Due to combined effects of low density and hypersonic flight conditions, the gas in the shock-layer is in a state of thermal and chemical nonequilibrium. The present work aims at gathering existing ideas together about how such flows should be modeled and comparing them to recent, more accurate experiments that probe the separate energy modes of the different species of the gas in a more direct way than previously reported.; Two recent Bow-Shock-Ultra-Violet flight experiments, and two recent shock-tube experiments are used to test the validity of the flow-field models implemented in the current state-of-the-art numerical codes. They involve highly non-equilibrium flow regimes in nitrogen and air with negligible ionization and provide detailed spectra emitted by the hot gas.; A recent plasma torch experiment at Stanford, and the Cochise experiments at the Geophysics Directorate laboratories, have been the ideal experimental counterpart to test and improve the radiation calculation in the UV-visible spectral range and the IR region respectively. Each spectral region is used to probe several different aspects of the thermal and chemical nonequilibrium.; A hierarchy of flow-field codes has been developed in conjunction with a greatly enhanced radiation code, termed NEQAIR2, to simulate these experiments. The flow-field codes involve axisymmetric Navier-Stokes and Burnett simulations around blunt-nose cones for the flight experiments and quasi-1D Euler simulations for the shock-tube experiments. They include between 5 and 8 chemical species and between 3 and 6 separate internal energy modes. The corresponding system of conservation equations are solved with finite volume, flux split algorithms. Gauss-Siedel line relaxation is used to increase efficiency of the fully-implicit method and exact numerical jacobians have been derived to increase the rate of convergence. The radiation code involves a collisional-radiative model based on a quasi-steady-state (QSS) approximation and a detailed line-by-line calculation for several atomic systems and molecular band systems. Comparisons of numerical spectra with the flight data show good agreement at the lower altitudes but the predictions are only within an order of magnitude at higher altitudes.