In order to investigate effects of volute tongue tip radius on performance and hydraulic load characteristics, unsteady flow fields in a centrifugal pump with the same impeller but different volutes in five tongue tip radii were simulated numerically. The hydraulic performance, pressure pulsation, blade loading and radial thrust on the impeller were acquired and analysed, and the predicted perfor-mance was compared with the experiment results, showing the numerical methods adopted in the paper were in a better accuracy. The results showed that the tip radius had a little effect on the hydraulic performance, but the best hydraulic efficiency could be achieved at a certain tip radius. When the dimensionless tip radius TR(tip radius-to-base circle radius ratio)was in a range of 0.09-0.24, the loa-ding across the blade pressure side and suction side was the minimum, i.e. the force acting on a blade exhibited the least variation from the leading to trailing edges. With increasing TR, the pressure fluctuation level in the pump reduced gradually, particularly the pressure amplitude at TR=0.03 was about 2 times the amplitude at TR=0.3 for blade passing frequency. The tip radius has a significant effect on impeller radial thrust. At the nominal flow rate, the radial thrust increased with increasing tip ra-dius, and at TR=0.3 the thrust was about 2.5 times the thrust at TR=0.03.
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