Non-equilibrium Kinetics and Its Influence on the Parameters of Nozzle Flows

Establishing of strongly non-equilibrium conditions in molecular gas flows in nozzles and jets is connected with rapid gas cooling and essential differences between the relaxation times for translational and internal degrees of freedom. Under the conditions of sharp expansion of a preliminarily heated gas, the flow is accelerated, whereas its pressure and temperature drop dramatically. Due to the significant discrepancy between the relaxation rates of the translational and internal modes, the vibrational energy in each elementary volume of a moving gas varies considerably slower than the translational energy, and cannot achieve the value corresponding to the equilibrium state at a local gas temperature. As a result, the vibrational energy appears to exceed translational substantially, and the relaxation processes display the regime of strong vibrational excitation. In expanding flows, the non-equilibrium distributions of molecules over the vibrational levels occur also as a result of chemical reactions, particularly recombination, which becomes more important with a decrease in the temperature.