Comparison of Shock/Cooling-Film Interaction for Cooled and Isoenergetic Injection

High-speed particle-image velocimetry measurements and temperature measurements are performed to investigate the interaction of shock waves with film cooling flows at varying injection temperature. A laminar jet is tangentially injected beneath a turbulent boundary layer at a freestream Mach number Ma infinity =2.45. Two cooling film injection Mach numbers Mai are considered, Mai=1.2 at a total temperature ratio T0,i/T0,infinity =0.8 and Mai=1.8 at a total temperature ratio T0,i/T0,infinity =0.76. For the low injection Mach number, the shock is generated by a flow deflection of beta =5 degrees; for the high injection Mach number, the flow deflection angle is beta =8 degrees. For both injection Mach numbers, two shock impingement positions are investigated. For comparison, literature data with comparable shock parameters and isoenergetic injection are considered. The current results show that the flow structure of the shock/cooling-film interaction is highly sensitive to the injection temperature. The increased blowing rate at a lower injection temperature, that is, increased streamwise mass flux in the cooling film, drastically stabilizes the flow. This prevents mean separation and leads to reduced turbulent mixing downstream of the shock interaction region. In consequence, the turbulent heat transport toward the wall decreases, which implies a higher cooling effectiveness when the injection temperature decreases. The findings also show that flow cases with different injection temperatures but similar near-wall mass flux yield separation bubbles with similar streamwise extent.