The Effects of Relative Motion, Blade Edge Radius and Gap Size on the Blade Tip Pressure Distribution in an Annular Turbine Cascade With Clearance

Flow visualisation and microscopic static pressure measurements were done in the tip clearance region of an annular turbine cascade with a rotating outer casing to simulate the relative motion at the tip of an axial rotor. The effect of relative motion did not have a significant effect on the blade gap pressure distributions. As in previous studies the narrow deep pressure depression on a sharp pressure edge was seen. It was confirmed that the width of the gap separation bubble depends on clearance and a correlation with flow visualisation showed that at the reattachment line there is the expected slight pressure peak. The separation bubble, which is thought to contribute a major part of the leakage loss, was shown to disappear when the pressure surface tip is give a radius of 2.5 gap widths.Copyright © 1988 by ASME