Kinetic Phenomena in Spherical Expanding Flows of Binary Gas Mixtures

Diffusion and kinetic effects in the spherical expanding  ows of argon–helium mixtures have been studied using the direct simulation Monte Carlo technique at the Knudsen numbers from 0.0015 to 0.03 and pressure ratios from 100 to 10,000. Similarity analysis was used to analyze the  ow structure in supersonic  ow region, spherical shock wave, and subsonic area behind it. Both kinetic and diffusion effects in uence the shock-wave thickness, parallel and transverse species temperatures, diffusion velocities, the effectiveness of species separation, and ambient gas penetration. In the supersonic region the effect of “freezing” the parallel temperature has been found in all considered cases. The temperature freezing comes Ž rst for heavier molecules of argon. The transverse temperature for both species follows the temperature in the isentropic expansion. Accumulation of the hot light (helium) component occurs in the leading front of the spherical shock wave. The multitemperature regime of the  ow inside the shock wave is found and studied using the similarity factor, which is based on the ratio of stagnation pressures calculated at critical-source- ow and background conditions.