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Gas dynamics with relaxation effects

The way in which gas-phase chemical reactions and the excitation of internal modes of molecular energy storage can be collectively described as relaxation processes is explained. A set of equations which is suitable for a general account of gas flows with relaxation processes is exhibited. The dissipative-dispersive character of acoustic waves and the exploitation of the acoustic approximation in studies of flow problems are described. The effects of a non-equilibrium atmosphere on acoustic wave propagation, and the consequent possibility of exponential amplification of disturbances, is considered with reference to explosion and combustion phenomena, as well as a possible link with upper-atmosphere gravity waves. The analysis and explanation of shock-wave structure is briefly discussed using Hugoniot curves and Rayleigh lines. Gas flow in convergent-divergent nozzles, and multiphase flow phenomena are also considered.