On the numerical modelling of the transitional ow in rare ed gases

The aim of this work is to simulate rare ed gas ow in complex geometries, under ow conditions that range from the hydrodynamic, through the transitional, to the molecular regimes. Existing computational models apply to molecular or viscous ow, but the treatment of the transitional ow is still underdeveloped. To deal with the di cult transitional ow, two models with overlapping ranges of applicability are introduced. A direct simulation Monte Carlo (DSMC) type model, which can be used in the molecular and up to the lower transitional ow, has been designed. For the viscous to the upper transitional ow, a numerical model using a particle method is proposed. The objective is to obtain a smooth transition between the probabilistic simulation of particle histories and the deterministic approach of the solution of partial di erential equations. The DSMC model has been successfully applied to molecular and lower transitional ow in a complex geometry with stationary and moving boundaries. The test results agree well with published data. The particle method was tested using simpli ed Navier–Stokes equations in a channel. Preliminary results in the low viscous range seem to indicate that the approach is viable. c © 1999 Elsevier Science B.V. All rights reserved.