Experimental study of endwall and tip clearance flows in a two - dimensional turbine rotor blade cascade - effect of incidence angle

Abstract

Experimental investigations were carried out on a two-dimensional cascade fitted with a 120 ° deflection rotor blades to study the effect of incidence angle on the endwall flow in the presence of tip clearance. A total of five incidence angles, namely: -10 °, -5 °, 0 °, 5 °, 10 ° were chosen and for each incidence angle, the experiments were conducted for five tip clearance values at a constant space -chord ratio of 0.79. The results are presented in the form of contours of static pressure coefficient on the endwall and the blade tip surface. In addition, the variation of static pressure coefficient ahead of the blade leading edge and from the pressure surface to the suction surface at various axial stations, and discharge coefficient at different axial stations are presented. The results indicate that the adverse pressure gradient upstream of the leading edge is reduced as tip clearance is increased. The contours of static pressure coefficient on the endwall indicate a deep low-pressure trough near the suction surface in comparison to the normal trough for zero clearance. Loading also increases as incidence changes from the negative to positive values. Due to area contraction caused by the tip separation vortex, the fluid moving towards the tip gap from the pressure side is accelerated. Downstream of the tip separation vortex, the endwall pressure increases due to flow mixing. The maximum value of discharge coefficient increases and the point at which maximum value occurs shifts towards leading edge when incidence is changed from -10 ° to 10 °.

Study of Sweep and Induced Dihedral Effects in Subsonic Axial Flow Compressor Passages—Part II: Detailed Study of the Effects on Tip Leakage Phenomena

“…Govardhan et al [7] observed the blade loading to decrease substantially just under the blade tip surface. The effect was found to be pronounced when the tip clearance is increased.…”