Variations of stall mechanism induced by the changes of tip clearance size in a subsonic compressor rotor

Abstract

The clearance flow is closely linked to the tip flow characteristics and instability mechanisms of axial compressor rotor. Therefore, both experimental and numerical studies were conducted to investigate the influences of variations in clearance size on tip flow behaviors and instability mechanisms within a subsonic compressor rotor. The results show that the subsonic rotor has two distinct low-velocity zones due to tip leakage flow and suction surface separation at near-stall condition. As clearance size increases, suction surface separation decreases while tip leakage flow increases continuously. Within the small clearance size range (SCS range), the energy of leakage flow remains significantly lower than that of the surrounding mainstream at near-stall condition, leading it to be expelled from the tip channel by the mainstream. Thus, the substantial separation near suction surface induced by a pronounced positive angle of attack at leading edge, becomes the primary factor for tip flow instability in rotor at near-stall condition. Conversely, as clearance size further increased into large clearance size range (LCS range), suction surface separation nearly vanished near blade tip at near-stall condition, and the strong tip leakage vortex then dominates major disturbance in tip region. The low-velocity fluids generated by leakage vortex during unsteady fragmentation and dissipation obstructs the incoming mainstream in tip channel, contributing significantly to rotor stall. Consequently, it’s this progressively increasing leakage flow that leads to the stall margin of rotor showing an increasing and then decreasing trend in the clearance size monotonically increasing process, and fundamentally changes the stall inducing mechanism of the subsonic compressor rotor.