Numerical Simulations of Gas Cloud Expansion in Rarefied Environment

Dean C. Wadsworth ERC, Inc., Edwards AFB, California 93524 Time accurate numerical simulations of a high temperature source cloud of gas expanding into an ambient atmosphere are performed using a multiple temperature gas model and the direct simulation Monte Carlo (DSMC) method. The multi-temperature approach uses continuum conservation equations derived from the Boltzmann equation via first-order Chapman-Enskog expansion and zero-order non-isotropic velocity distribution function. These equations are solved numerically using a kinetic flux splitting method for inviscid fluxes and a central difference scheme for the viscous fluxes in a time accurate manner. The DSMC technique is a well-established particle approach for rarefied flows. The source and ambient densities and temperatures are varied to establish the range of applicability and relative accuracy of the two methods. For most of the source and the ambient parameter considered, the two methods give similar predictions of the basic flowfield evolution, and of the degree of translational non-equilibrium that arises.