Effect of volute tongue on unsteady flow in a centrifugal pump

The unsteady flows in the Volute of a single-stage, cantilevered centrifugal pump with specific speed of 93 have been mapped by using LDV at both best efficiency and part-loading points respectively while pumping water. The results show that the water velocity fluctuates periodically with the impeller sweep angle with respect to measuring points where the flow field will be investigated. As the distance between impeller tip and measuring points increases. the peripheral component of water velocity damps rapidly. becomes more and more uniform, and its periodical fluctuation is suppressed continuously. The magnitude in the fluctuation is about 30% - 70% of the local mean velocity. The fluctuation magnitude in the flow angle is larger than the magnitude in velocity by an order of 1-2. The more closed, the measuring point approaches to the volute tongue. the larger the fluctuations in velocity and flow angle become. and this results in a more and more heavy effect on the unsteady flow. The fluctuations in the velocity and flow angle at part-loading point are larger than at best efficiency point. The flow pattern is non-axis-symmetrical along the impeller periphery. The flow is diffused in the volute. However. the flow velocity is more uneven. its velocity gradient is more severe and flow diffuses more heavily at part-loading point than that at best efficiency point.