Low-frequency fluctuation propagation of rotating stall in the centrifugal compressor and pipe system

Abstract

The characteristic signal judgment of rotating stall in a centrifugal compressor is necessary to avoid the compressor becoming instability in operation. This study investigates rotating stall in a centrifugal compressor and pipe system using experimental and numerical simulation methods. In the experiment, a low-frequency (approximately 10% of the impeller's rotational frequency) pressure fluctuation is observed in the inlet and outlet pipes as the pressure ratio curve declined at small flow rate. The frequency spectrum results of different measuring locations suggest that the low-frequency disturbance is in the flow direction within the pipe system during rotating stall. To further analyze this pressure fluctuation, a transient numerical simulation of the centrifugal compressor with plenum model is conducted. Rotating stall can be captured by the numerical model, and the low-frequency pressure fluctuation is also observed in the transient simulation, aligning with the experimental results. The periodic evolution of the tip leakage vortex influences the flow in the impeller passage, causing a fluctuation in the flow direction that propagates upstream and downstream as revealed by flow field analysis. The low-frequency pressure fluctuation in the inlet and outlet pipe system is a characteristic signal, which can be a new stall judgment of rotating stall in the operation of centrifugal compressor.