Numerical investigation of transition delay in a Mach 6 boundary layer using porous walls

The main emphasis of this work is to investigate the effect of the porous wall on the nonlinear stability regime and to determine if the nonlinear stages of transition are affected by porous walls. Temporal direct numerical simulations were carried out for a Mach 6.0 boundary layer on a smooth and porous wall geometry. An Immersed Interface Method was implemented in a compressible Navier-Stokes code to physically resolve the porosity. The resonance onset behavior for fundamental and subharmonic breakdown was compared. Fundamental resonance was found to be stronger than the subharmonic resonance. For highly resolved breakdown simulations a strategy was adapted where the resolution was successively increased as the flow evolved from a laminar to turbulent state. In addition, the effect of numerical filtering on the transition simulations was investigated.