Effects of casing air injection on film cooling and aerodynamic performances of an axial turbine cascade

Abstract

Rotor casing injection is one of the technical means for tip leakage flow control and casing thermal management. In the current investigation, a series of numerical simulations with the unsteady sliding mesh method are conducted to illustrate the effects of injection location, tip clearance, and shaped injection hole on the aerodynamic and cooling performance of casing air injection in an axial turbine cascade, under three injection mass flow ratios (0.15%, 0.30%, and 0.45%). The results indicate that the casing injection at X/Ca = 0.1 performs the best in reducing the tip leakage mass flow rate, but the highest isentropic efficiency appears when the injection holes are located at X/Ca = 0.3. The increase of the tip clearance is detrimental to the aerodynamic and film cooling performances of the casing injection scheme. Moreover, the application of shaped holes (converging slot hole and fan-shaped hole) plays a positive role in improving film cooling effectiveness and increasing isentropic efficiency. Especially under a large coolant to mainstream mass flow ratio of 0.45%, the results show that the fan-shaped hole improves the spatially-averaged casing film cooling effectiveness by approximately 16% relative to the cylindrical hole.