Abstract: In order to study the effect of the tip leakage flow under different tip clearances on the flow structure of the semi-open impeller centrifugal pump, five different tip clearance size schemes were designed. The SST k-ω turbulence model was used to calculate the whole flow field of the semi-open impeller centrifugal pump. The internal flow structure of the semi-open impeller tip clearance under different working conditions was analyzed and verified by visualization experiment.The results show that with the decrease of the tip clearance, the head and efficiency of the centrifugal pump significantly increase, but when the clearance value is reduced to 0.7 mm, the pump efficiency no longer changes significantly with further decrease of the tip clearance. Choosing the optimum value of the tip clearance has a certain inhibition effect on the development of leakage vortex. It can be found by using the Q criterion to discriminate vortex, as the clearance decreases, the strength of the main tip leakage vortex weakens, the secondary tip leakage vortex in the mainstream channel gradually disappears, and the disturbance to the mainstream decreases. When the clearance is reduced to 0.7mm, the secondary leakage vortex completely disappears, and the strength of the main leakage vortex is the weakest. The degree of interference of the leakage flow at the blade tip on the flow field is affected by the flow rate. At low flow condition, by reducing the tip clearance, the anti-interference ability of flow in the blade region can be improved.

Key words: semi-open impeller, centrifugal pump, tip clearance, high speed camera