Effects of Simulated Rotation on Tip Leakage in a Planar Cascade of Turbine Blades: Part II—Downstream Flow Field and Blade Loading

Abstract

This paper and its companion paper present experimental results on the effects of simulated rotation on the tip leakage in a linear turbine cascade test. Part II examines the downstream flow field. For clearance sizes of 2.4 and 3.8 percent of the blade chord, measurements were made in two planes downstream of the trailing edge using a seven-hole pressure probe. Significant changes in the tip leakage vortex and passage vortex structures are observed with the introduction of relative motion. The effects of clearance size and rotation on the relationship between bound circulation and tip-vortex circulation are discussed. The validity of a previously developed tip-vortex model for the case of rotation is examined in the light of the measurements. Finally, for clearances of 1.5, 2.4, and 3.8 percent of the blade chord, the effects of rotation on blade loading are studied through static pressure measurements on the blade surfaces. The distortion of the surface pressure field near the tip is found to be reduced with increasing wall speed. This is consistent with the reduced strength of the tip-leakage vortex as wall speed is increased. For all measurements two wall speeds are considered and the results are compared with the case of no rotation.