DIRECT SIMULATION OF VORTEX SHEDDING IN DILUTE GAS-FLOWS PAST AN INCLINED FLAT-PLATE

The vortex shedding in dilute gas flows past an inclined flat plate is studied using the null-collision direct-simulation Monte Carlo (DSMC) method. It is shown that the DSMC method is capable of generating large-scale vortices even for the collision-cell size considerably greater than the mean free path, provided that an average molecular number per cell is sufficiently large. There exists the cell-size effect that the vortex structure becomes more obscure and the decay length of large-scale vortices becomes shorter with an increase in the collision-cell size. The Strouhal number evaluated from the vortex shedding process for the free-stream Mach number M∞ = 0.7 and Knudsen number Kn∞ = 1/60 and 1/200, for which the Reynolds number Re∞ = 69.2 and 231, respectively, is about 0.2. It is found that large-scale vortices disappear at a rather small Mach (M∞ ≳2 for Kn∞ = 1/60) or Knudsen (Kn∞ ≳0.1 for M∞ = 0.7) number. © 1990 American Institute of Physics.