Abstract：In order to investigate into the internal unsteady flow of low specific speed centrifugal pump at various low flow rates, a series of numerical simulations of DES(detached eddy simulation)in an end-suction centrifugal pump of type IS50-32-160 are carried out on the basis of analysis on grid independence. The results show that the tongue has a more important influence on the internal flow in the impeller, causing different size vortices exist in three flow passages near the tongue; the vortices just behind the impeller inlet are close the blade suction side with the same rotation direction as the impeller, but the vortexes near the impeller outlet are in front of the blade pressure side in the reverse direction of the impeller. With declining flow rate the vortexes expand so fast that even block the whole passage, especially in the three passages near the tongue. Meanwhile, a flow separation emerges in the volute nozzle, resulting in a non-uniform outflow. A FFT(fast Fourier transformation)frequency transformation is conducted for the pressure signals picked up at the monitoring points in the impeller and volute, and it is found out that the dominated frequencies in the impeller are the shaft frequency and its integer multiples, and the amplitude of pressure pulsation increases steadily with the radius and from the suction side to the pressure side. In contrast, the dominated frequencies in the volute are the blade frequency and its integer multiples, the more violent the amplitude of pressure pulsation, the smaller the distance to the tongue, eventually, the greatest pulsation occurs on the tongue. The intensity of pressure pulsation at all the monitoring points gets stronger with decreasing flow rate.
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