Cubic Fokker-Planck-DSMC hybrid method for diatomic rarefied gas flow through a slit and an orifice

• Published in: Vacuum 2019-01, Vol.159, p.125-133
• Main Author: Jun, Eunji
• Format: Article
• Language: English
• Subjects: Diatomic gas flow; DSMC; Fokker-Planck-DSMC hybrid; Rarefied gas dynamics; SPARTA; Vacuum flows
• ISSN: 0042-207X; 1879-2715
• DOI: 10.1016/j.vacuum.2018.10.028

Fokker-Planck kinetic models have been devised as an approximation of the Boltzmann collision operator. Cubic Fokker-Planck-DSMC hybrid method is employed to simulate the diatomic gas flow through a thin slit and a thin orifice. Pressure driven nitrogen expansion gas flows with two different pressure ratios are investigated at Knudsen number 0.001. The DSMC method is physically accurate for all flow regime; however it is computationally expensive in high density or near continuum regions. The Fokker-Planck-DSMC hybrid scheme employs DSMC in rarefied regions and Fokker-Planck method in near continuum flow regions for an efficient and accurate solution. Numerical procedures of the cubic Fokker-Planck method are implemented within the framework of an existing DSMC-solver, SPARTA. The Fokker-Planck-DSMC hybrid solution reproduces pure DSMC solution with improved computational efficiency up to a factor of five for vacuum flow through a thin orifice. In addition, breakdown of translational equilibrium is investigated. Domain criterion of FP-DSMC is safely smaller than Bird's breakdown criterion. •Rarefied diatomic gas flow through a thin slit and a thin orifice.•Access of accuracy and efficiency of cubic FP-DSMC for diatomic gas flow.•Investigation of breakdown of translational equilibrium on cubic FP-DSMC hybrid.•Comparison of diatomic and monoatomic flow through a thin slit and a thin orifice.