The Effect of Wall Suction on the Efficiency of Transpiration Cooling in Hypersonic Boundary Layer Flow

Aerodynamic heating and early transition remain critical concerns in hypersonic boundary layer flows. While transpiration cooling offers effective thermal protection by introducing coolant through a porous wall, it can also enhance flow instabilities, particularly at higher blowing ratios. This study uses Direct Numerical Simulations of a Mach 7.7 flow over a flat plate to examine how coolant injection and suction influences boundary layer receptivity and disturbance growth. By introducing controlled disturbances downstream of the injection zone, the analysis tracks the evolution of generalized inflection points (GIPs) and wall pressure fluctuations. The effect of the combined use of blowing for cooling and suction on the receptivity and thermal performance of transpiration cooling is analyzed through the streamwise evolution of the disturbance modes and the distribution of cooling effectiveness on the surface. Results show that can promote the downstream growth of instabilities at specified spanwise wavenumbers; however, the simultaneous application of suction patches appears to damp these modes in the cases with coolant injection. Moreover, while suction has been observed to reduce wall cooling performance locally near the suction region, shifting the suction patch to an upstream location appears to lead to a better recovery of the cooling effectiveness further downstream.