Effect of rotor blade tip clearance on aerodynamic performance of high-speed multi-stage axial compressor

Abstract

Using a high-speed multistage scale model compressor simulating a middle stage of a gas turbine compressor for power generation, the effects of 3 types of rotor tip clearances on performance and operating range, and the vortex structure of rotor tip leakage vortices were investigated numerically and experimentally. To clarify the mechanism of the unsteady development of tip leakage vortices from vortex breakdown to stall cells, which was confirmed to occur in the condition of largest tip clearance, details were investigated by unsteady numerical analysis. In both CFD and experiments, the tip leakage loss increased rapidly when the tip clearance increased, and the load increased. The tip leakage flow is determined by the tip clearance and differential pressure between suction and pressure side. Under the condition of the largest clearance, the axial momentum of the tip leakage flow decreases with increasing blade load. At this time, a rapid increase in loss was observed at the 30 %chord of the rotor, suggesting that the double leakage increased and the backflow from the trailing edge reached the mid-chord position of the adjacent blades, contributing to the increased loss. At the condition of the highest-pressure ratio of the largest clearance, vortex breakdown occurred. Spiral vortex breakdown of the tip leakage vortex causes the vortex to swing and then begin to interfere with the adjacent blade leading edge, and the vortex feet attach to the adjacent blade pressure side and the blockage develops. This starts the generation of spillage and initiates the formation of a stall cell.

Keywords

• axial compressor
• tip clearance
• tip leakage
• loss
• rotating stall
• stall inception
• cfd