Translation-vibration-dissociation coupling in nonequilibrium hypersonic flows

This paper is a study of the relationship between the rate of dissociation of a diatomic molecule and its translational and vibrational state. A simple and computationally efficient model is developed to describe the evolution of vibrational states during relaxation and dissociation. The di atomic molecule is described by two vibrational levels: a lower level made up of molecules whose vibrational energy is less than a cutoff energy, and an upper level whose vibrational energy is greater than that energy. The lower level relaxes according to Landau-Teller theory and the upper level is populated from the lower level due to vibrational transitions. Dissociation occurs from the upper level and recombination to the lower level. The parameters required for the model are taken from a simulation of the vibrational state of a rotationless nitrogen molecule undergoing relaxation performed by Sharma, Huo, and Park¹, The model is implemented for a constant translational temperature relaxation problem, whereby nitrogen is allowed to relax vibrationally and dissociate or recombine to equilibrate to a fixed temperature. Cases are compared to the previous simulation and to results obtained using previously developed translation-vibration-dissociation coupling models. The model has also been implemented in a quasi-one-dimensional computational fluid dynamics algorithm. The flow behind a shock and in a nozzle are com pared using the different coupling models. The results obtained indicate significant differences between the models.