Study of cavitation-induced flow characteristics of a vortex pump based on coherence analysis

Cavitation-induced flow instabilities in vortex pumps critically degrade hydraulic performance and operational lifespan. This study investigates the evolution of the vapor cavities within vortex pumps across various cavitation states using both numerical simulations and experimental analysis. The unsteady flow dynamics within the impeller channel are examined, and the relationships among pressure pulsations, vortex volume, and vapor volume fraction are analyzed. As cavitation intensifies, the vapor volume expands progressively. Notably, the time required for the vapor to expand during critical cavitation is twice as long as that for severe cavitation, whereas the contraction time is one-fourth. The variation in vortex volume inside the impeller follows a distinct pattern, initially increasing and then decreasing, with the peak occurring during critical cavitation. The interactions between pressure pulsations, vapor volume fraction, and vortex volume become increasingly complex, especially during severe cavitation, where the amplitude of pressure pulsations significantly decreases, the vapor volume fraction increases, and vortex volume fluctuations are suppressed. Wavelet coherence analysis reveals the coupling dynamics of these three variables across different temporal scales and frequency bands, with enhanced coherence observed in the low-frequency range (0-50 Hz). These findings provide valuable insights for the optimization and development of vortex pumps in municipal and industrial fluid transport applications.