Numerical Simulations of Nonequilibrium and Diffusive Effects in Spherical Shock Waves
Introduction: Relaxation Effects in Expanding Gas Flows
Experimental studies of underexpanded N 2 jets ,  discovered a delay of rotational temperature T R compared to the translational one T t . A drop in the gas density downstream leads to a decrease in the number of collisions and the T R departure from the equilibrium value , . Another cause for the T R departure  could be explained in terms of quantum concepts. Because of the T t plunge, the adiabatic collision conditions are realized at a certain temperature, rotational-transfer probabilities begin to decrease , and the relaxation time τ R increases. Calculations based on the classical concept , ,  do not show a tendency of increasing τ R with the decrease of T t under the adiabatic rotational energy exchange conditions. Computational results , , based on the quantum concept of energy exchange, correlate well with experimental data  of T R distribution along the jet axis.
In the present study, the flow from a spherical source is used as the approximation model of the flow in underexpanded jets  and spherical shock waves. Rotational relaxation effects are analyzed by using the continuum approach and classical models  at T t > 100 K and quantum approach  at T t < 100 K. In addition, diffusive kinetic effects in spherical flows of Ar-He mixtures are studied. These effects are important in studies of separation processes in jets and physics of explosion.
KeywordsShock Wave Pressure Ratio Continuum Approach Length Scale Parameter Spherical Source
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