Effects of bulk flow pulsations on film cooling with shaped holes

Experimental results are presented which describe the effects of bulk flow pulsations on injectant behavior and film cooling performance around shaped holes with compound angle orientations. The shaped holes have a 15 degrees forward expansion with an inclination angle of 35 degrees. The orientation angles considered are 0 degree, 30 degrees, and 60 degrees. The pulsation frequency is fixed at 32 Hz, but changes in the time-averaged blowing ratios of 0.5, 1.0, and 2.0 produce three different coolant Strouhal numbers. Flow visualization shows that bulk flow pulsations cause significant periodic variations of the injectant flow rate, and produce severe crossflow ingestion at a high coolant Strouhal number. Although shaped holes show improved film coverage compared to round holes under steady condition, shaped holes are so sensitive to flow pulsations that a drastic reduction in the film cooling performance is observed at a high coolant Strouhal number.