Numerical investigation of porous walls for a Mach 6.0 boundary layer using an immersed interface method

Temporal direct numerical simulations were carried out for a Mach 6.0 boundary layer in order to investigate the effects of porous walls on stability and transition. To model the porous wall, a novel immersed interface method was implemented into the compressible Navier-Stokes Solver developed in our laboratory. Grid convergence studies were carried out to ensure that the resolution for the immersed interface simulations was sufficient. The simulation results demonstrate that the immersed interface method is well suited for investigating the effects of porous walls. Furthermore, a comparison of the results obtained with our immersed interface method with those reported in the literature for the linear stability regime, shows very good agreement. Additionally, the different terms in the kinetic disturbance energy equation were analyzed for the smooth wall and porous wall cases in order to gain physical insight into the stabilization mechanisms of porous walls. The results suggest that the pressure diffusion and viscous dissipation are the two most relevant mechanisms responsible for stabilization. In addition to investigating the effect of the porous walls on the linear stability regime, we also studied their effects with the nonlinear behavior and nonlinear breakdown mechanisms. Our simulation results for a fundamental breakdown scenario indicate that porous walls may also be effective in mitigating secondary instability mechanisms, and thus final breakdown to turbulence. However to confirm this, other breakdown mechanisms need to be investigated as well, such as for example, the subharmonic and oblique breakdown.