Analysis of Inducer Recirculating Inlet Flow

Abstract

The mean and turbulent features of inducer inlet e ow covering various operating points of a centrifugal pump are analyzed. Measurements are conducted in an air test facility with a e ve-hole pressure probe and an X-wire probe. For e ow rates lower than the design e ow rate, the recirculation located upstream of the inducer is very strong and creates a global rotation of the e uid from the tip to the hub, upsteam of the inducer. The axial extent of the separated e ow decreases as the e ow rate increases. The stagnation pressure in this region is higher than the upstream stagnation pressure and can reach several times the inlet dynamic head. In the inlet channel axis, within the recirculated e ow, the stagnation pressure is lower than what is found for upstream stations outside the recirculation. This can be related to upstream e uid motion and mixing with the inverse e ow, providing stagnation pressure losses. For the e ow rates where the recirculation region is large, the incoming e ow is dee ected toward the hub. Phase-averaged measurements in the inducer inlet show the main time-dependant e ow features and their evolutionwiththee owrate.Theanalysisshowsthat,atdesign andhighere owrates,theevolution ofthemeridional velocity is correlated with the evolution of the relative e ow angle. Relative velocity is not affected by the blade leading edge and is constant at a given radius. The change in the axial velocity is mainly due to the sudden change of the relative e ow angle before the blade leading edge.