Abstract: Detailed measurements were carried out upstream, downstream and in the middle plane of tip clearance in three types of cascades: conventional straight blade cascade, positively curved blade cascade and negatively curved blade cascade. Flow visualization was also carried out on the blade surface and endwall surface. By comparison with the conventional straight blade cascade, the experimental results show that : (a) In positively curved blade cascade, leakage flow and crossflow near the endwall were decreased, up passage vortex disappeared, and secondary vortex separation type changed from closed separation to an open one; as a result, leakage flow through tip clearance and mixing losses downstream were decreased. (b)In positively curved blade cascade, leakage flow through tip clearance was also cut down, but mixing losses downstream were increased because of the strengthened interaction among leakage vortex, up passage vortex and secondary vortex.

Key words: turbine cascade, cur ving blade, clearance flow, ex perim ent al study