Discussion and Verification on the Cause of Inlet Secondary Backflow Under Partial Load of Centrifugal Pumps

To discuss the cause of inlet secondary backflow of centrifugal impellers under partial load and its effect on centrifugal pump performance, the pressure distribution of forced vortex, the causes of inlet secondary backflow and the influence of impeller inlet backflow on the characteristics of the pump were analyzed by using theoretical and experimental methods. Numerical simulation and analysis of a pump with a specific speed of 66 was performed by using a verified computational fluid dynamics (CFD) technique. The pressure and velocity vector distribution of impeller inlet were analyzed at different flow rates. The external characteristic curves of two pumps with different blade leading edge were compared to analyze the influence of the inlet secondary backflow on the external characteristics of the pump. The results show that the pressure in the forced vortex rises along a parabolic trajectory as the radius increases. The cause of the secondary backflow is that the pressure differences on different radius caused by the rotation impeller forming a forced vortex of the viscous fluid at the entrance of the impeller under partial load. And the secondary backflow at the inlet of the impeller have certain effects on eliminating the hump of H-Q curve, which is a positive phenomenon. Therefore, it plays a certain role for the formation and mechanism of inlet backflow under partial loads of centrifugal pumps, and provides some reference for further research of centrifugal pump.