Stability Investigation of High-Speed Boundary Layer Flows with Transpiration Cooling Through Porous Media

Hypersonic vehicles operating within the atmosphere are subjected to extreme thermal loads, which can be mitigated using transpiration cooling - a technique that injects coolant gas or liquid through the vehicle surface. While this heat mitigation strategy can be effective in reducing surface temperatures, it can also alter boundary layer stability and potentially trigger an earlier transition to turbulence. Since the surface temperature and blowing characteristics of a transpiring coolant depend on both the external flow field and the properties of the porous material, this study investigates, for the first time, the effects of gas injection through a realistic porous structure on high-speed boundary layer stability. The gas transport within the material and the thermal response are resolved using a high-fidelity coupled CHAMPS-KATS fluid–material interaction solver. The resulting surface blowing velocity and temperature distributions are then used as boundary conditions for a separate linear stability analysis. Air injection is evaluated at multiple mass flux levels under both ground-based wind tunnel and stratospheric flight conditions over a moderately blunt cone geometry. LST and time-spectral analysis shows a strong effect on second-mode growth with a stabilization in the injection region and destabilization downstream of the injection region.