Numerical analysis of the cavitating flow in an axial flow waterjet pump with special emphasis on the tip leakage flow and tip leakage vortex

Due to the structural design requirements, tip leakage flow is a common phenomenon in the field of axial flow rotating machinery. The tip leakage flow interacts with the mainstream and induce complex tip leakage vortex. When the local pressure drops to the saturation pressure, cavitation may occur in flow passage and the vortex core. The tip leakage cavitating flow has a huge effect on the flow stability, which may reduce the efficiency of the waterjet pump. In the present study, Zwart cavitation model and SST k-ω turbulence model are employed to simulate the cavitating flow. The new proposed Liutex criterion has been used to capture the vortex structures in the flow passage and the tip gap. The vorticity transport equation in cylindrical coordinates is also used to discuss the variation tendency of the vorticity in the vicinity of the gap region under cavitation condition. The evolution of the cavitation is proved to be vital important for the formation and the breakdown of the tip leakage vortex. By analyzing the vorticity transport equation, the stretching term is shown to be the decisive factor.