Tip Leakage Losses in Subsonic and Transonic Blade Rows

Abstract

In this paper the effect of bladeexit Mach number on unshrouded turbine tipleakage flows is investigated. Previously published experimental data of a highpressure turbine blade are used to validate a computational fluid dynamics (CFD) code, which is then used to study the tipleakage flow at bladeexit Mach numbers from 0.6 to 1.4. Threedimensional (3D) calculations are performed of a flattip and a cavitytip blade. Twodimensional calculations are also performed to show the effect of various squealertip geometries on an idealized tip flow. The results show that as the bladeexit Mach number is increased the tipleakage flow becomes choked. Therefore the tipleakage flow becomes independent of the pressure difference across the tip and hence the blade loading. Thus the effect of the tipleakage flow on overall blade loss reduces at bladeexit 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 tipleakage loss.