Aerodynamic performance of suction-side squealer tip in impulse/reaction turbine blade rows

Abstract

In order to understand the impact of turbine reaction on the SS (suction-side squealer) tip loss, the loss map for the SS tip with the variations of both tip clearance and squealer height is completed in the blade row of medium turbine reaction (exit-to-inlet velocity ratio, VR = 2.0), and then the present SS tip losses are compared with the previous ones in the blade rows of weak and strong turbine reactions (VR = 1.2 and 2.4). The SS tip loss map shows that the loss change with squealer height is not so large and its maximum loss reduction is less than2.9% of flat tip loss. Regardless of tip clearance and squealer height, the present SS tip performs worse than the full squealer tip in the loss reduction for VR = 2.0, and this performance gap is more noticeable for wider tip clearance. The comparisons of the present SS tip losses for VR = 2.0 with those for VR = 1.2 and 2.4 show that the SS tip-to-flat tip loss ratio is influenced strongly by VR (reaction) of impulse/reaction turbine blade row. Irrespective of squealer height, the SS tip has a considerable loss reduction only in the blade row of VR = 2.4. Especially for low squealer heights without structural defect, the SS tip-to-flat tip loss ratio continues to decrease, as VR increases from 1.2 to 2.4. The present over-tip flow visualizations give a clear explanation about tip gap flow physics in the blade rows of different VR.