Aerothermochemical Nonequilibrium Modeling for Oxygen Flows

Abstract

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 twotemperature model is presented as the computationally efficient, lower-fidelity approach in this work. The twotemperature 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.

Kinetic and Continuum Modeling of High-Temperature Oxygen and Nitrogen Binary Mixtures

“…For nitrogen, the authors are not aware of such data; for oxygen, there are incident shock wave experiments [6] and reflected shock wave experiments [14] for oxygen-argon mixtures. For incident shock waves, in particular, it was found [91,92] that modern absorption diagnostics [6] may not offer sufficient resolution to distinguish between low-and high-fidelity models for shock velocities below 4.5 km/s. For reflected shock waves, accurate capturing of time-resolved interactions of an incident shock with the wall is necessary [93], thus requiring a modification in the numerical algorithm such as that proposed for the DSMC method [93].…”

Vibrational non-Boltzmann effects on the dissociation rate of oxygen

“…Although the computational power of STS limits its application in large-scale calculations, the STS method can still give details of the variation of the number density of molecules at different states in thermochemical nonequilibrium processes, which provides the possibility to specifically study the NB effects on the dissociation and to propose improved models, for example, improved models that combine the results of the STS calculation method with traditional models, or reduced-order STS methods. Neitzel 18 developed a 2-T model for oxygen considering the NB effects based on the simulation results of STS. Panesi 19,20 et al proposed the coarse-grained model, which divides the molecular energy states into groups and determines the distribution of states within the groups according to the maximum entropy criterion, and describes the NB effects using the vibrational temperatures between the groups.…”