Analysis of flow measurements in the impeller and vaned diffuser of a centrifugal pump operating at part load.

In a recent european contract, four impellers with different specific speeds have been equiped with transparent front shrouds in order to obtain optical access to the flow between the blades. The presented results are the last analysis of internal flow measurements in one of these impellers (Ns32) fitted with a vaned diffuser. They are especially related with the interaction between impeller and diffuser, e.g. the phenomenon of flow separation, wakes, and backflow inside the pump. Unsteady velocity measurements were carried out in the hydraulic laboratory of CETIM with the help of laser doppler velocimetry technique. The data fields have been treated by the CNAM-LEMFI in order to give instantaneous view of the Bow between the blades. From these pictures, a three dimensionnal movie has been built, that allows to explain some details in the behaviour of centrifugal impeller between 0.2Qn and Qn.