Experimental Study on Cavitation Flow Structures of Water-jet Pump

This study presents an experimental investigation into the cavitation flow structures within a water-jet pump, conducted using high-speed photography on a closed-loop test platform. The study captures the temporal evolution of cavitation structures and identifies five typical types: Sheet Cavitation, Cloud Cavitation, Tip Clearance Cavitation, Tip Vortex Cavitation, and Perpendicular Cavitation Vortex (PCV). The evolution of these cavitation structures under varying Net Positive Suction Head available (NPSHa) conditions is analyzed in detail. Based on a combined analysis of cavitation performance curves and flow visualizations, the study reveals that increased cavitation causes the expansion and interaction of PCVs, which block blade passages and result in significant flow separation, ultimately leading to substantial reductions in head and efficiency. Furthermore, the study establishes a quantitative correlation between cavitation vortex structures and pump performance, thereby providing a scientific basis for predicting cavitation-induced degradation. Based on binarized high-speed photography images, the study quantitatively measures vapor volume fractions at various cavitation stages, revealing the relationship between cavitation region expansion and pump performance degradation. It thereby provides visual evidence of cavitation development. This work offers valuable insights into the mechanisms of cavitation evolution and provides engineering guidance for improving the performance of water-jet pumps.