Research in Engineering and Aviation

Tip-leakage losses in subsonic and transonic blade rows. Journal of Turbomachinery

October 2012

Author(s): Wheeler, A.P.S., Korakianitis, T., & Banneheke, S.

Journal: Journal of Turbomachinery, 135(1), art. no. 011029. DOI: 10.1115/1.4006424

Abstract

In this paper the effect of blade-exit Mach number on unshrouded turbine tip-leakage flows is investigated. Previously published experimental data of a high-pressure turbine blade are used to validate a computational fluid dynamics (CFD) code, which is then used to study the tip-leakage flow at blade-exit Mach numbers from 0.6 to 1.4. Three-dimensional (3D) calculations are performed of a flat-tip and a cavity-tip blade. Two-dimensional calculations are also performed to show the effect of various squealer-tip geometries on an idealized tip flow. The results show that as the blade-exit Mach number is increased the tip-leakage flow becomes choked. Therefore the tip-leakage flow becomes independent of the pressure difference across the tip and hence the blade loading. Thus the effect of the tip-leakage flow on overall blade loss reduces at blade-exit Mach numbers greater than 1.0. The results suggest that for transonic blade rows it should be possible to raise blade loading within the tip region without increasing tip-leakage loss.

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