Analysis of backflow effect in a centrifugal pump

Abstract

Backflow might appear near the impeller inlet under low discharge conditions due to excessive pressure difference near the blade leading edge. The shear layer between the swirling backflow and the main flow rolls up and forms a backflow vortex at the impeller’s inlet. Backflow vortex cavitation occurs at the vortex core if the pressure there drops lower than vapor pressure. In order to investigate the effect of backflow on pressure, flow rate and cavity volume, the backflow phenomena for a centrifugal pump was calculated using SST k-omega turbulence model and Rayleigh-Plesset cavitation model. Results show that the general flow characteristics are correctly predicted. Furthermore, the development of cavities and backflow have been illustrated in this paper. It is also shown that the backflow occurring at the inlet of impeller significantly affects the general performance of the centrifugal pump. The generation and collapse of the cavities caused by the backflow lead to the oscillation of cavity volume, which is the main reason for large-cycle fluctuation of inlet flow rate.