The nonequilibrium modeling of reflected shock tube flows is investigated, motivated by hypersonic vehicle design. Oxygen nonequilibrium behavior is the focus of the work due to its contribution to modeling uncertainty, specifically the vibrational-translational energy transfer process of the O_2-Ar system. Two levels of vibrational nonequilibrium modeling fidelity are evaluated. The lower fidelity model is the two-temperature model that uses Millikan-White vibration relaxation rates to capture the vibrational nonequilibrium process at the macroscopic level. The higher fidelity model is the state-resolved master equation method that uses vibrational state-to-state rates to explicitly calculate the vibrational state distribution throughout the analysis. The vibrational state-to-state rates are evaluated using the forced harmonic oscillator (FHO) model and a detailed quasi-classical trajectory (QCT) analysis. The nonequilibrium models are implemented in two flow solvers to analyze reflected shock tube experiments. First, a simple method is employed of chaining two post-normal shock analyses together to simulate the vibrational nonequilibrium behavior of a particular parcel of fluid in the reflected shock tube. Second, the nonequilibrium models are implemented in a 1-D unsteady flow solver to capture the entire behavior of the reflected shock tube. Comparisons are provided between results obtained with the two different flow solvers, and the three different physical models, for two different shock tube conditions.
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