The direct simulation Monte Carlo of flows composed of asymmetric potential scatterers

Abstract

Predicted fluid transport properties are dictated by the assumed interaction-potential model between molecules. The direct simulation Monte Carlo (DSMC) method has been developed principally for those potentials that may be included efficiently in computational terms. In this paper nonisotropic scattering models are investigated for the Couette flow, with both shear stress and heat flux being calculated; the results are then compared to those predicted by the variable hard sphere (VHS) and the variable soft sphere (VSS) models. The same procedure is then repeated for a shock wave flow case. It is concluded that, even when extreme post-collision directionality is modeled, statistically similar results to VHS and VSS models are obtained if the total collision cross section and its variation with temperature are appropriately normalized. This demonstrates the important result that to achieve convergence with the measured transport properties of heat flux and viscosity, as well as with shock flow structures then highly precise molecular models are not required for DSMC. Conversely, the adoption of different scattering models, attempting to simulate specific features of the underlying physics of a collision, may not always be achieved using the DSMC method. Variation of the total cross section with temperature is a well-recognized phenomenon included in all successful models for molecular processes. Of itself, however, this variation does not determine the post-collision partners, rather it influences the rate at which processes can occur. As a result it is contributive to, rather than the determinant of, the physical outcome from a collision.