A detailed model for hypersonic iodine vapor flow with vibrational as well as chemical nonequilibrium has been developed to assess the impact of vibrational nonequilibrium in a hypersonic wind tunne nozzle. The modeling approach described in this paper can be applied to flows involving diatomic molecules, including those with significant dissociation and recombination. Commonly used finite-rate chemistry computer programs which do not normally treat vibrational nonequilibrium can be used to model vibrational nonequilibrium by including vibrational transition reactions, written in the same format as chemical reactions. Each discrete vibrational level is treated as a separate species and reaction rate expressions are developed for vibration-vibration (V-V), vibration-translation (V-T), and dissociation reactions using various reaction rate models. Vibrational equilibrium, harmonic oscillator, SSH, and modified SSH thermodynamic and reaction rate models have been developed for iodine. One-dimensional and two-dimensional finite-rate chemistry nozzle calculations have been made using the LPP (Liquid Performance Program) nozzle analysis code. The V-T transitions were found to be dominant when compared to V-V transitions for the conditions evaluated. Vibrational population plateaus were seen in the nozzle even when V-V reactions were excluded from the model, having been caused by the coupling between V-T transitions and recombination. Calculations have been performed to investigate behavior of the flow models in the chemical and vibrational relaxation region behind a hypersonic normal shock.
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