Parametric study of tip cooling injection in an axial turbine cascade: Influences of injection circumferential angle

Abstract

This article presents a parametric investigation of an innovative tip-clearance control method. Cooling air is injected into the tip clearance to obstruct tip clearance flow, from the blade tip surface through a row of 11 equidistant holes. In order to demonstrate the influences of injection circumferential angle, four different test cases are performed and compared with the baseline case without air injection. The results indicate that injection circumferential angle plays an important role in the redistribution of secondary flow within the cascade passage. Injection at a smaller circumferential angle performs better in reducing tip clearance mass flow and its associated losses. However, it also intensifies the tip passage vortex much more, because of the reduced restraint deriving from the weaker tip clearance vortex. It can also be found that flow under-turning caused by the tip clearance vortex can be reduced greatly with a smaller circumferential angle. But the heat transfer condition is worse than that when cooling air is injected perpendicularly to the blade tip surface. Besides that, a modified tip clearance loss model is observed to be able to perform well in predicting the losses induced by tip clearance flow at all the conditions considered in this article.