Experimental and Numerical Investigation of Recirculation Flows at Impeller Inlet and Outlet of a Centrifugal Pump Operating at Part-load

The flow field inside a centrifugal pump at part load operation has been investigated both experimentally and numerically in order to highlight the onset and the growth of recirculations taking place at the impeller inlet and outlet. Recirculation phenomena interact with the blade passages and have a significant effect on the characteristic curves of the machine. The recirculation at the impeller discharge is not generated by the impeller itself. The flow pictures returned by the numerical analysis show that a flow separation occurs in the conveyor channel close to the elbow from where the backward progressively approaches the runner as the flow rate diminishes. The stationary blades forming the conveyor channels seem not to have a prominent role on the development of the reverse flow since the numerical data highlight a comparable recirculation near the elbow even when the stationary vaned systems is removed from the computational domain. The recirculation arising at the impeller inlet is caused by the excessive incidence angle of the incoming flow on the leading edge of the blades. The distinct origins of the recirculations at both the inlet and the outlet of the impeller make the back flows independent from each other.