Cubic Fokker-Planck-DSMC hybrid method for diatomic gas flow through a slit

Abstract

Rarefied gas flows through a thin slit have attracted great practical and scientific interest because they have many engineering applications, e.g. vacuum equipment, microfluidics, spacecraft design, metrology of gas flow etc. Extensive numerical investigations have been studied on pressure driven gas flow through a thin slit by applying DSMC. Recently proposed kinetic Fokker-Planck (FP) models approximate the inter-particle collisions by a stochastic process, which permits using a larger cell size and time step than would be required by DSMC in flow domains where the local Knudsen number is less than unity. Furthermore, a coupled FP-DSMC solution method has been developed aiming at an efficient and accurate solution algorithm for rarefied gas flows. In this research, pressure driven Argon gas flow through a thin slit will be investigated over the wide range of gas rarefaction covering the free-molecular, transitional and near continuum regime by applying DSMC, FP and FP-DSMC hybrid schemes. We consider a slit which separates two reservoirs. One of them contains a gas at a pressure P0 while the other is maintained at a smaller pressure P1. Four different pressure ratios (P1/P0 = 0, 0.1, 0.5, 0.9) and 6 different degree of rarefaction are considered. A detailed analysis and comparison of accuracy of standard DSMC and cubic FP solution is performed. Then, the near-continuum cases with various pressure ratios are simulated with FP-DSMC hybrid scheme. Accuracy and efficiency of FP-DSMC hybrid scheme are discussed in a detailed study.