Numerical Investigation on Rotating Instability in a Transonic Compressor Under Low Reynolds Number Conditions

In high-altitude conditions, the decrease in atmospheric pressure and density causes the inlet Reynolds number of the compressor to rapidly decrease. This makes it easier for the flow shear layer on the blade surface to separate, which in turn affects the aerodynamic stability of the compressor. In recent years, the issue of rotating instability (RI) in compressors operating near stall conditions has attracted significant attention from researchers. In this study, a transonic rotor is simulated to investigate the generation and propagation mechanism of rotating instability at low Reynolds number. By setting standard atmospheric conditions at 0km and 20km as boundary conditions respectively to simulate ground and low Reynolds number conditions, and unsteady calculations are performed at the near stall condition under different operating conditions. Utilizing approaches such as circumferential mode decomposition to assess the frequency spectrum and mode of RI, the study elucidates the RI phenomenon in association with the unstable flow structures at the blade tip. The leading edge vortex is generated through the interaction of the shock wave and the tip leakage vortex. As the leading edge vortex advances downstream and encounters the pressure surface of the subsequent blade passage, the reverse leakage vortex emerges, thereby initiating the development of rotating instability.The findings indicate that: The Reynolds number plays a crucial role in the formation of RI. The interaction between the reverse leakage vortex and the main leakage vortex in the flow field generates an unstable structure, leading to the formation of RI. At low Reynolds numbers condition, RI progresses towards lower frequencies and mode numbers, resulting in a decrease in circumferential propagation velocity.