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An accurate algorithm is proposed to improve the prediction of a particle incollision with a moving wall within the direct simulation Monte Carlo (DSMC)framework for the simulation of unsteady rarefied flows. This algorithm is ableto predict the particle-wall collision in a coupled manner by removing theassumption employed by the approximate algorithm, in that the wall is frozenduring the collision. The trajectory equation of the particle is theoreticallyconstructed in a moving object coordinate system. It can accurately describethe geometries of the collision between a particle and an arbitrarily shapedobject of which the motion incorporates both translation and rotation, thusallowing to deal with complex problems. In contrast, the approximate algorithmignores the effect of the moving wall on the particle movement during thecollision, and therefore induces error that is an increasing function of thewall velocity. Four rarefied flow problems are applied to validate the accuratealgorithm. It is shown that the algorithm can produce results perfectlyconsistent with the Maxwellian theoretical solutions and ensure particleconservation to avoid gas leakage. It is also shown in a three-dimensional caseof a re-entry module that the steady simulation fails to reproduce thehysteresis effect while the unsteady simulation using the accurate algorithmcan do that, indicating that the unsteady simulation with an appropriatealgorithm as proposed in the present work is essentially required in suchapplications.

An accurate moving wall boundary algorithm for Direct Simulation of Monte Carlo in unsteady rarefied flow