In order to analyze the effects of tip clearance on the flow and performance of low specific speed highspeed centrifugal pump with a semiopen impeller, the inner flow field in a pump with the specific speed ns=19.3 was numerically simulated based on the Navier-Stokes equations and the Spalart-Allmaras turbulence model at the tip clearances 0.5, 1.1 and 2.5 mm. The performance of the centrifugal pump was measured as well.The results show that the flow in the impeller is improved with a bigger clearance, but the hydraulic loss caused from the circular flow in the impeller at a relatively big clearance is larger than that at a more tight clearance, so the head and efficiency were decreased with increasing tip clearance. Also, the relative velocity and static pressure of fluid in the clearance were reduced at the middle and trailing edge of blade with increasing tip clearance, especially the relative velocity. The static pressure shows a nearly linear relation to radius. The tangential and radial velocity along the axial direction in the impeller passages were lowered with increasing clearance. Comparison of the results simulated with the experimental data suggests CFD method is quite able to simulate a change in the performance due to varying tip clearance.
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