Study of Tip Clearance Effects on Performances and Flow Field of a Low Specific Speed Mixed-flow Pump

To explore the tip clearance effects on performance and flow field of the low specific speed mixed-flow pump, tip clearance δ of 0.25 mm, 0.75 mm and 1 mm, along with no tip clearance, are selected. The steady flow was simulated with ANSYS-CFX for the whole flow passage of a mixed-flow pump with a specific speed of 149. The structured mesh of the computation domain is generated with ICEM-CFD and TurboGrid, post-processing is done with Tecplot software. The results show that the effects of tip clearance on performance parameters in large flow rate conditions (1.25Q_d, 1.5Q_d) are greater than that in small flow rate conditions (0.5Q_d, 0.75Q_d), and an approximate parabolic relationship is obtained between the ratio of efficiency reduction to tip clearance variation(Δη/Δδ) and the relative discharge m; When the tip clearance value is 0.75 mm, as the discharge increases, the vortex forms near the impeller passage inlet and gradually moves toward the impeller outlet. Meanwhile, the vortex intensity and its influence range on the mainstream are increased. More serious entrainment effect is happened between the leakage flow and the mainstream when the tip clearance increases to 1 mm.