Abstract: A centrifugal pump used as a turbine is a core power component of the seawater desalination energy recovery machine; its pressure pulsation during operation is a major factor causing vibration and noise. This paper presents full-passage numerical simulations of the three-dimensional unsteady flows in a high rotating speed centrifugal pump as a turbine using a SAS-SST-CC turbulence model. We discuss the unsteady flow characteristics through flow field analysis and pressure fluctuation spectrum analysis. The results show the dominant frequencies of pressure pulsation at multiple measuring points in the volute are the same as the blade passing frequency, indicating the pulsation comes largely from the dynamic and static interference between the runner and volute tongue. Among the six measuring points located in each of the 8 blade channels of the runner, the maximum difference in the peak-to-peak amplitudes at the corresponding positions is 10.3%, revealing a significant uneven feature of flow distribution in the runner. The pulsation frequencies at these rotating measuring points are largely the dominant frequency or secondary dominant frequency near the frequency of 8 times the blade frequency, indicating the dynamic and static interference between the runner and volute is significant. Vortices in the blade channels are the main factor causing pressure pulsation in the runner, and these local vortices cause pressure pulsation stronger than those from the dynamic and static interference of the runner. The results show that pressure pulsation in the runner is more severe than that in the volute, and the former is the main hydraulic cause of unit vibration.

Key words: seawater desalination, high speed pump as turbine, CFD, internal flow characteristics, pressure pulsation, vortex, dynamic and static interference