Investigations of a discrete velocity gas
Abstract
A new model of molecular gas dynamics with discrete molecular velocity components was implemented for parallel computation. Calculations of molecular motions are thereby simplified. The outcome of binary collisions between particles is determined by reflections about axes of symmetry in the centerofmass frame of reference. The procedure speeds calculations of collisions. Of interest is the insight the discrete model provides into complex physical behavior and the effect that physically realistic simplifications have on the accuracy and speed of parallel calculations of a flow. The equilibrium state of a discretevelocity gas and the influence of limited velocity resolution are explained. The time development of nonequilibrium velocity distribution functions is presented. The model is applied to unsteady flows involving strong shock waves, heat transfer between solid surfaces, and unsteady shear layer development. When the model is applied to gas mixtures, numerical experiments show that the required number of values of each component of molecular velocity depends strongly upon the mass ratios of the particle species involved. However, fewer than ten values of each velocity component are necessary to produce results of satisfactory accuracy in calculations of a shock wave in a single species gas. A unique, selfadaptive mesh for parallel computation, used either for the present lattice gas model or earlier directsimulation Monte Carlo models, is described. The mesh balances the load between the processors of the multicomputer and maintains the cell size at approximately a fixed number of local mean free paths throughout the flow field.
 Publication:

Ph.D. Thesis
 Pub Date:
 1990
 Bibcode:
 1990PhDT........20G
 Keywords:

 Computational Grids;
 Distribution Functions;
 Flow Distribution;
 Gas Dynamics;
 Gas Flow;
 Gas Mixtures;
 Mathematical Models;
 Velocity Distribution;
 Computerized Simulation;
 Heat Transfer;
 Parallel Processing (Computers);
 Shear Layers;
 Shock Waves;
 Solid Surfaces;
 Unsteady Flow;
 Fluid Mechanics and Heat Transfer