Comparative study of tip leakage vortex trajectory and cavitation in an axial flow pump with various tip clearances

In order to analyze the effect of blade tip-gap size on the tip leakage vortex (TLV) dynamics and TLV-induced cavitation, a scaled axial flow pump model was created and numerically studied by the combination of an improved SST k-w turbulence model and a homogeneous cavitation model. The trajectories of TLV core was obtained by using the swirling strength method at different tip-gap sizes vary significantly. The scale of TLV increases as the tip-gap size increases, and the starting point of TLV is sliding further downstream along the blade chord. The angle between the blade suction surface and the TLV also presented an increasing trend with the tip-gap size. The statistics of the velocity normal to the tip chord, as well as the turbulent kinetic energy (KTE) distributions were employed to illustrate a more disordered flow field, which was generated in the tip clearance in a larger amount of leaking flow due to the increased tip-gap size. The in-plain static pressure and vapor volume fraction distributions at different blade chord sections, coupled with three-dimensional cavitation patterns among three tip gaps, are further analyzed to verify the wandering motion of TLV, which shows good agreement with the visualization experiment. Considering the adverse effect of the TLV cavitation, a small tip gap is recommended for improving the axial flow pump performance.