Investigation into the flow mechanism of rotating instability in a subsonic axial flow compressor rotor

Abstract

Experimental and numerical investigations on a subsonic axial flow compressor rotor are carried out to clarify the flow mechanism of rotating instability (RI). RI is observed at the narrow stable operating range near the stability limit of the test rotor for the experiments. The simulation results show that RI appears near stall condition, which is similar to that in the experiments. An unsteadiness of tip leakage flow (TLF) is detected in a passage for the numerical results. Its characteristic frequency agrees well with the dominant mode frequency of RI in experiment. Details of the simulated flow fields indicate that the unsteadiness of TLF is induced by the interaction between TLF and the loading of blade tip in a single passage. This process propagates circumferentially against the rotor and forms a traveling wave in the circumferential annulus, which is responsible for RI. Since the blockage effect increases with decreasing mass flow rate, the fluctuation region of TLF gets larger, the period of flow unsteadiness increases and the parameters of RI vary.