Experimental Investigation of the Pre-Stall and Stall Evolution in a Centrifugal Compressor With a Volute

Stall and surge behaviors deteriorate the compressor performance and stability of the operating range. To avoid the effect of stall and surge behaviors, the characteristics of the pre-stall disturbance have been considered in recent years. However, investigations of the pre-stall and stall disturbances in centrifugal compressors remain insufficient owing to the various geometric structures in centrifugal compressors. In this study, a centrifugal compressor with a volute and vaneless diffuser was studied using high-response static pressure measurements and numerical simulations. The pressure disturbance evolution from near-choke to near-surge conditions was obtained, and the characteristics of the pre-stall and stall disturbances were analyzed. The results showed that the compressor instability route could be divided into pre-stall and stall stages, which could be accurately predicted based on the periodic static pressure irregularity and skewness. The pre-stall stage was dominated by the rotating instability (RI) phenomenon, and the frequency of the RI was 43% of the blade passing frequency at 70% N-max. The experimental results demonstrated that the first onset of RI occurred at the 120 deg-180 deg circumferential position and maintained a local pattern; then, RI occurred over the whole annulus when the flowrate was decreased. RI was induced by the vortex structure attached to the casing wall, leading to a sharp pressure trough in the static pressure trace. The RI exhibited an evolution pattern of initially increasing and then fading, which can be explained by the enlargement and movement of the impeller inlet vortex. The large blockage effect of RI triggered a stall with disturbances at 20% and 80% of the impeller shaft frequency, and these disturbance frequencies had a trend of shifting to one dominant frequency of 22% the impeller shaft frequency. Furthermore, stall cell merging and the coexistence of RI/stall phenomena occurred during the stall stage.