Aerothermochemical Nonequilibrium Modeling for Oxygen Flows

The results from a set of vibrational nonequilibrium models with a range of fidelity are compared to the recent experimental data for several postnormal shock test cases. The present work focuses solely on oxygen flows with an emphasis on implementing a new set of accurate state-specific rate coefficients for O-2-O collisions. The two-temperature model is presented as the computationally efficient, lower-fidelity approach in this work. The two-temperature model is driven by the relaxation parameters based on the Millikan-White empirical equation as well as on the parameters resulting from a master equation simulation that employs the database of state-resolved O-2-O rate coefficients. The full state-to-state master equation approach is presented as the higher-fidelity modeling approach. The O-2-O system uses recently available results of trajectory simulations for state-specific transition rate coefficients The O-2-O-2 system uses transition rates from the forced harmonic oscillator model. The test case comparison shows that the state-resolved modeling approach is more suitable for describing the vibrational temperature and chemically nonequilibrium zone behind the shock wave. It is shown that the capability of the state-resolved model to capture non-Boltzmann distribution is critical for accurately modeling the vibrational relaxation and dissociation phase.