Tip leakage flow, tip aerodynamic loading and rotating instability in a subsonic high-speed axial flow compressor rotor

Abstract

Rotating instability as an unsteady flow phenomenon is closely related to rotating stall in the compressor. In this paper, dynamic pressure measurements and full-annular URANS simulations were conducted in a subsonic axial flow compressor rotor to enhance the understanding of the flow mechanism of RI. RI characterized by a frequency band in the spectrum is detected at a narrow stable operating range in the experiments. The monitoring results from simulations show that RI characterized by a frequency hump in the spectrum appears near stall condition which is consistent with the observation in the experiments. RI shifts to lower frequency band in the rotating frame with the decrease of mass flow rate. Details of the numerical flow field indicate that RI develops synchronously with the oscillation of the tip leakage flow (TLF). The tip leakage vortex (TLV) forms a low static pressure near the pressure surface side of neighboring blade through an induced vortex. It varies the tip aerodynamic loading. Both the tip aerodynamic loading and TLF get strong with the decrease of mass flow rate. The stronger TLV will form a stronger induced vortex near the pressure surface side of the neighboring blade and propel the induced vortex toward the leading edge of blade. When a high tip aerodynamic loading region is influenced by the induced vortex near the pressure surface side, the intensity of TLF in the next passage will be weakened. Then, TLF fluctuates and leads to the oscillation of neighboring blade tip aerodynamic loading as well as the oscillation of TLF issuing from the neighboring blade. The circumferential propagation of this influence process results in RI.