Experimental Study on the Correlation Between Unstable Flow and Cavitation Vibration of Pump-Wheel Cascade

In order to deeply reveal the coupling mechanism of flow and cavitation evolution inside the pump–turbine under hump conditions, this paper combines numerical simulation of multiphase flow with high-speed imaging experiments and systematically analyzes the structure of non-constant flow and its induced hydraulic excitation behavior. It is found that as the cavitation number decreases from 0.33 to 0.072, the vacuole morphology in the impeller develops from incipient bright spots to U-shaped cavitation clouds, and vortex cavitation and lamellar cavitation meet at the trailing edge, which triggers a strong perturbation in the flow channel. At the same time, large-scale flow separation develops on the pressure surface, accompanied by intensified vortex structures on the suction surface and a highly non-uniform circumferential velocity distribution at the guide-vane inlet. These flow distortions significantly increase the hydraulic excitation of the system. The three-dimensional connection and asymmetric distribution of the vacuoles exacerbate the load imbalance between the channels, which is the main cause of efficiency loss and structural vibration enhancement. The pressure pulsation spectrum is accompanied by multiple high-frequency and low-frequency excitation peaks, especially in the 20–33 Hz band, which reveals the multi-source coupling mechanism between cavitation behavior, reflux shear, and modal response. The results provide theoretical support for the in-depth understanding of the instability evolution mechanism of the pump–turbine and operation optimization under complex working conditions.