Dynamic evolution process of rotating stall vortex based on high-frequency PIV system in centrifugal impeller

Abstract

Rotating stall is a kind of strong unstable flow phenomenon, which plays a decisive role in stable operation of centrifugal pumps. Limited by the performance of the experimental system, so far there are rare experimental studies on the rotating stall phenomenon in impeller, especially the initial generation and the evolution process of the rotating stall vortex. Based on the experimental bench with refractive index matching and the high-frequency PIV system, the continuous instantaneous velocity fields were visualized in a five-blade impeller. Two kinds of experimental measurement methods were utilized to observe the formation process and study the transmission mechanism of rotating stall vortex between impeller passages. Meanwhile, the Proper Orthogonal Decomposition method is used to smooth the instantaneous velocity field. The results show that the generation of the rotating stall in impeller is a transient process. The flow rate in each passage adjusted quickly when the impeller enters the stall stage, and then the stall vortex moved periodically along the impeller at a certain frequency. Two kinds of frequency characteristics of the stall vortex were clearly observed at stall conditions. The relationship between the evolution frequency of the stall vortex under different impeller speeds and flow rate is reasonably explained.