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.