Effect of rarefaction on axial vortex using direct simulation Monte Carlo

The effect of rarefaction on the axial vortex inside a lid-rotating closed cylinder is studied in the present work. The Direct Simulation Monte Carlo (DSMC) method has been used to simulate the flow inside the cylinder. The cylinder is closed and filled with Argon gas. Here, we look at the effect of rarefaction and compressibility on such flows by varying the Knudsen number (Kn) and Mach Number (Ma) of the flow. The Kn of the flow has been varied from 0.025 to 0.5 for Ma of 0.75 and 1 for a fixed aspect ratio of the cylinder 2.5. Thermal transport is characterized as the function of Ma and refraction. A three-dimensional Navier-Stokes-Fourier (NSF) solver with appropriate temperature jump and velocity slip boundary conditions has been used to compare the DSMC result for Kn=0.025. It is seen that DSMC and NSF results agree with each other at this low Kn. Note that increasing Kn reduces the peak axial velocity uz, as less momentum is transferred from the top plate to gases due to rarefaction. The velocity slip between the cylinder wall and the adjacent layer of fluid increases with an increase in Kn. Effect of rarefaction on radial pressure distribution has been discussed. The torque acting on the bottom plate was found to be decreasing with increasing rarefaction. The effect of rarefaction on flow topology and other regimes are also discussed.