Effect of cooling injection on the leakage flow of a turbine cascade with honeycomb tip

Abstract

The effects of the cooling injection with various injection positions and angles on the tip leakage flow have been numerically studied in an axial turbine cascade with honeycomb tip. The coolant is injected through the bottom hole into each honeycomb cavity and coupled with the internal vortices to obstruct the leakage flow. Tip leakage mass flow rate and total pressure loss coefficient at the cascade exit are used to evaluate the aerodynamic performance of the tip design. Nusselt number and adiabatic film cooling effectiveness are chosen for the thermodynamic evaluation. Numerical results show that the injection position and angle play an important role in affecting aerodynamic and thermodynamic performance, especially for the injection positioned near downstream sidewall or with small injection angle in the center. Compared with the flat tip, tip leakage mass flow rate drops by up to 26.7%, and total pressure loss coefficient is reduced by about 4.6%. Furthermore, the tip leakage vortex approaches the suction surface, resulting in reduced affected area and weakened loss strength. Meanwhile, the heat transfer performance of the honeycomb tip is improved, especially for the inclined injection with small injection angle in the bottom center.