1. National Research Center of Pumps, Jiangsu University, Zhenjiang, Jiangsu 212013, China; 2. Shandong Shuanglun Co., Ltd., Weihai, Shandong 264200, China
Abstract：In order to explore the inner unsteady flow characteristics of the vertical inline pump during the power-off transition process, the numerical simulation method coupled with a Fortran program based on the commercial CFD code CFX was adopted to predict the flow motions in the pump. The angular momentum differential equation was used to predict the variation law of the rotating speed. The flow rate, rotating speed and other parameters as well as the flow velocity distributions during the transient process of the power-off and shutdown of the pump were analyzed. The results show that after power failure, the speed gradually decreased from positive speed to reverse speed and increased to runaway speed(nmax=1.206 n0). There was a delay between the speed and the flow rate, the former reached the zero point 1.24s later than the latter; the amplitude of pressure pulsation reached the hig-hest value in the runaway stage. At the beginning of the transition process, several vortices were observed in the inlet passage, impeller channel and volute. In the middle stage, the vortex gradually disappeared, and the flow pattern tended to be stable. In the later stage, small vortices appeared in the inner side of the second bend and the outlet of the curved inlet pipe. The research reveals the transient flow features in the process of the inline pump shutdown, which provides a fundamental theory for the safe operation of pump shutdown.
