State-to-state description of reacting air flows behind shock waves

•State-to-state kinetics in shock heated air flows is studied.•The results found within accurate and reduced kinetic theory models are compared.•The new effect of the vibrationally excited free stream is found.•The free stream excitation dramatically changes the relaxation zone structure.

In the present paper, non-equilibrium flows of the 5-component air mixture N2(i)/O2(i)/NO(i)/N/O behind shock waves are studied taking into account the state-to-state vibrational and chemical kinetics. Equations for the non-equilibrium kinetics including vibrational energy transitions, dissociation, recombination and Zeldovich reactions of NO formation are coupled to gas dynamic equations and solved numerically for different test cases of the re-entry conditions into the Earth atmosphere. Peculiarities of air parameters behind a shock wave formed in an initially vibrationally excited mixture are studied. Various models for state-dependent rates of kinetic processes are used for calculations and their applicability for prediction of flow parameters is discussed. The results obtained in the state-to-state approach are compared with those based on multi-temperature and one-temperature vibrational distributions and estimations for an accuracy of the simplified models are presented.

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