Experimental investigation of tip clearance effects on flow field in an annular turbine rotor cascade

The present paper reports results of an experimental investigation on the effects of tip clearance in a high deflection annular turbine rotor cascade. The measurements are carried out at the inlet, in the blade passage and at the exit of the cascade using a five-hole probe and a seven-hole probe. The results indicate that the incoming flow to the rotor cascade is uniform and the incidence is about ±2°. When the clearance is increased, the size and the magnitude of the tip clearance loss region increase. The flow near the hub experiences overturning, whereas near the casing the flow substantially underturns due to tip clearance. The underturning increases with tip clearance. Secondary and tip clearance losses steeply increase downstream of the blade trailing edge indicating losses due to the wake and clearance flow mixing with the main flow.