Non-equilibrium Kinetics and its Influence on the Transport Processes Behind Strong Shock Waves

Abstract

In Chapters 7-9, we consider the applications of the above-developed kinetic theory of transport and relaxation processes to some particular problems of non-equilibrium gas dynamics. In this Chapter, the peculiarities of the relaxation zone behind strong shock waves occurring in a hypersonic gas flow are considered. The rapid gas compression within a thin shock front with the characteristic length of about several mean free paths, results in a temperature jump which, due to the significant difference in relaxation times, occurs essentially without a variation in the mixture composition and molecular distributions over the vibrational energy. After that, in the relaxation zone behind the shock front, the excitation of vibrational degrees of freedom and chemical reactions take place, and as a result of relaxation processes, the total thermal and chemical equilibrium is established. The length of the relaxation zone reaches many tens and even hundreds mean free paths. The gas state in the unperturbed flow before the shock front is usually supposed to be equilibrium, and therefore, as a consequence of the gas propagation through the shock wave and relaxation zone, one equilibrium state is transformed to another. In the vibrational relaxation and chemical reactions behind the shock wave, equilibrium or weakly non-equilibrium distributions over the translational and rotational degrees of freedom established in the shock front are maintained. The assumed invariance of the Maxwell distribution corresponds to the Euler approximation for an inviscid nonconducting gas flow. Taking into account deviations from the Maxwell distribution makes it possible to study dissipative processes in a non-equilibrium viscous gas.

In this Chapter, we consider non-equilibrium vibrational distributions, macroscopic flow parameters, and dissipative properties of gas mixtures behind strong shock waves, in an A2/A binary mixture and in air, within the framework of the state-to-state, multi-temperature, and one-temperature kinetic models.