Velocity-Slip and Temperature-Jump Effects in Near-Continuum Hypersonic Flows

Velocity-slip and temperature-jump effects on sharp leading-edge geometries are studied for three canonical hypersonic flows: the hollow-cylinder-flare, the double-cone, and the double-wedge. Simulation results are compared between the direct simulation Monte Carlo (DSMC) method that naturally captures slip effects and computational fluid dynamics (CFD) using an appropriate slip model. Only the leading-edge portions of these flow configurations are studied. The simulations are verified to be converged in terms of grid and particle resolution. Overall, excellent agreement is found between DSMC and CFD predictions of the leading-edge boundary layer, the magnitude of velocity-slip and temperature-jump, and surface heat flux for all cases considered, with the exception of the double-cone case due to the relatively high Knudsen number of the flow. The largest discrepancies were found for the double-cone (transitional flow conditions), and near-exact agreement was found for the double-wedge (continuum flow conditions). It was determined that slip effects cannot account for the discrepancy between CFD predictions and experimentally measured heat flux for the hollow-cylinder flare. Furthermore, it was determined that the previously recommended threshold for the continuum breakdown parameter might be overly conservative in the near-wall region if appropriate slip models are used in CFD.