Cavitation surge driven by backflow-vortex cavitation in an inducer under low-flow conditions

Abstract

Cavitation surge under low-flow conditions is a major form of flow instability in inducer-equipped high-speed pumps, yet its spatiotemporal coupling with inlet backflow-vortex cavitation remains insufficiently resolved. In this work, synchronized high-speed visualization and pressure-pulsation measurements were employed to investigate the flow physics of cavitation surge in an inducer operated under low-flow conditions. The results show that cavitation surge is accompanied by the periodic growth, elongation, and collapse of large-scale backflow-vortex cavitation clouds in the inlet duct upstream of the inducer. This cyclic cavity evolution is closely correlated with a pronounced low-frequency pressure oscillation, indicating that the surge is more strongly associated with the unsteady dynamics of the backflow-vortex cavitation structure than with blade-passing-frequency fluctuations. As the available suction head decreases within the surge regime, backflow-vortex cavitation generally intensifies, the pressure-pulsation level increases, and the flow stability deteriorates. Cavitation surge is observed only in the low-flow regime and is closely associated with the formation of a fully developed, coherent backflow-vortex cavitation cloud at the inducer inlet. These results provide experimental evidence supporting a close physical link between periodic cavitation-cloud dynamics and cavitation surge and suggest that backflow-vortex cavitation is closely associated with low-frequency instability in inducer flows.