Computations of high-speed, high Knudsen number microchannel flows

The effect of varying the Knudsen number Kn in microchannel flows was simulated using the direct simulation Monte Carlo method (DSMC) combined with the monotonic Lagrangian grid (MLG). The DSMC-MLG, a method that provides automatic grid refinement according to number density, has been optimized for massively parallel computation and provides a fast, highly resolved description of the flow. New outflow boundary conditions, consistent with the DSMC-MLG algorithm, were developed to allow the user to specify the outflow pressures. The effect of varying Kn was examined for three different values of Kn (0.07, 0.14, and 0.19) for a high-speed inflow by varying the channel height. A Navier-Stokes computation was also performed to show continuum regime flow. The computations provide contours of pressure, temperature, and Mach number to show complex interactions among oblique shocks and boundary layers, and how these change with the Kn. Temperature jumps and slip velocities as functions of position along the wall are compared for all cases. The computations show that the velocity slip is approximately constant behind the shock, while the temperature jump is reduced.