EFFECTS OF BLADE CURVING ON CLEARANCE FLOW LOSSES

Detailed experimental investigations of the flows in the cascades of conventional straight blades and positively curved ones,both with 2.3% tip clearance,were carried out in a low speed wind tunnel.The measuring planes were arranged as 4 before,11 in 4 after the cascades and 1 in the middle of the tip clearance.Flows inside the clearance were searched in great detail with a micro five-hole pitot tube of 1mm head size and another of 5 mm head size in the passage.The quite detailed information about the tip leakage flows and the flows in the cascades has been obtained,such as flow vectors,pressure and loss distributions throughout the clearance and in the passage.In comparison with the conventional straight blades,positive blade curving decreases the flow vectors within the tip clearance and also reduces the strength of the leakage vortex.As a result,the mass flux crossing the tip clearance decreased,the interaction between leakage vortex and passage vortex in the curved cascade also decreased.Thereby,the total flow losses downstream of the curved blade have been cut down by 8%.