Methods for Desensitizing Tip Clearance Effects in Turbines

Abstract

This study is an attempt to reduce the effect of the leakage vortex in axial flow turbines. A 3D Navier-Stokes CFD solver with k-ε turbulence modeling was used compute the flow through an axial flow turbine with modified blade tip designs. A baseline flat tip case and three modified tip cases were simulated and the leakage flow and vortex for each was analyzed in detail. The three modified blade tip designs each involved adding a chamfer to the tip of the blade, in an attempt to diffuse the leakage flow through the gap and obstruct the leakage flow with the outer casing’s shear layer. Chamfering of the blade tip near the leading edge of the gap and across the entire gap region both failed to reduce the size and strength of the leakage vortex. By chamfering the blade tip near the trailing edge of the gap, the leakage flow inside the gap was turned toward the direction of the blade’s camber. This turning resulted in a decrease in the size and the strength of the leakage vortex and its subsequent losses, while at the same time, did not reduce the blade loading by an appreciable amount. This paper is available in color on the World Wide Web at http://navier.aero.psu.edu/∼jat/research.html