Vortex cavitation shedding mechanisms in an axial-flow pump: A Liutex-based numerical investigation

This study presents a numerical investigation into the shedding mechanisms of complex vortex cavitation in an axial-flow pump under extreme off-design conditions. Using the Liutex vortex identification method to accurately capture the vortical structures, we analyze the complete lifecycle of three distinct vortex cavitation: tip leakage vortex cavitation (TLVC), secondary tip leakage vortex cavitation (S-TLVC), and perpendicular vortex cavitation (PVC). The results reveal the underlying mechanisms responsible for the detachment of these cavitation structures. For TLVC, a reduced flow rate diminishes the circumferential kinetic energy of the tip leakage jet, which appears to cause the vortex to accumulate and transform into a twisted vortex (TV). The presence of cavitation further induces the formation of a spiral shape. The shedding of S-TLVC is suggested to be induced by an axial velocity gradient, resulting from uneven shielding between the cavitation protected front part and the jet-influenced rear part. Furthermore, PVC is suggested to originate from a re-entrant jet that forms following S-TLVC detachment; its interaction with the circumferential flow is likely to generate the perpendicular vortex and drives cavitation shedding. Notably, the periodic shedding of vortex cavitation is sustained by an alternating generation of S-TLVC and PVC, forming a cyclical pattern. These findings elucidate the coupled dynamics between vorticity and phase change during vortex cavity shedding and provide a theoretical basis for developing targeted control strategies to mitigate cavitation damage in fluid machinery.