Trailing Edge Shock Modulation by Pulsating Coolant Ejection

In transonic and supersonic turbomachinery, shock waves appear at the trailing edge, generating substantial losses due to the interaction with the boundary layer. A novel proposal to control the resulting fish tail shock waves consists on, pulsating coolant blowing through the trailing edge of the airfoils. This paper presents an unprecedented experimental and numerical research. A linear cascade representative of modern turbine bladings was specifically designed and constructed. The test matrix comprised four Mach numbers, from subsonic to supersonic regimes (0.8, 0.95, 1.1 and 1.2) together with two engine representative Reynolds numbers (4 and 6 106) at various blowing rates. The blade loading and the downstream pressure distributions allowed understanding the effects on each leg of the shock structure. Minimum shock intensities were achieved using pulsating cooling. A substantial increase in base pressure was observed for low coolant blowing rate. Analysis of the high-frequency Schlieren pictures revealed the modulation of the shock waves with the coolant pulsation. The Strouhal number of the vortex shedding was analyzed for all of the conditions.