Thermal performance improvement on winglet tip of a turbine stage under engine condition-part II: Ejection angle adjustment

Abstract

Part I has indicated that the vertical ejection causes pronounced coolant lifting-off effect on the winglet tip of turbine stage. To solve this problem, Part II presents the study on adjusting ejection angle to reduce thermal load on the winglet tip under engine condition. Three procedures were taken to realize the mitigation of thermal load on the winglet tip of turbine stage. Firstly, the streamwise ejection angle was varied to determine a suitable ejection angle for the majority of cooling holes. Secondly, different numbers of tip cooling holes were selected to adjust the ejection angles towards P.S. (pressure side), aiming at enhancing the film cooling effect at the front part of the cavity floor. Lastly, different P.S. deflection angles were tested to find the suitable streamwise ejection angles for the selected holes. The results show that the inclined coolant ejections are quite effective to reduce the thermal load on the winglet tip. As the P.S. defection angles for the tip cooling holes at the front part of the cavity floor equal to 60°, and the streamwise ejection angles for the other cooling holes are set to 120°, the lowest thermal load is achieved on the winglet tip of turbine stage. After adjustment, the area-averaged heat transfer coefficient on the tip surface is decreased by 38.84%, and the area-averaged film cooling effectiveness is increased by 42.24%, as compared with the vertical ejection case. Moreover, the uniformity of the coolant coverage on the winglet tip has been improved, significantly.