INVESTIGATION OF HYDRODYNAMIC-FORCES ON ROTATING AND WHIRLING CENTRIFUGAL PUMP IMPELLERS

A two-dimensional fluid model is developed to investigate the hydrodyn amic forces exerted on a rotating impeller caused by the impeller-flui d-volute interaction in a centrifugal pump. In this model, the impelle r periphery and the volute contour are replaced by a distribution of u nsteady vortices. The impeller center is assumed to execute a whirling motion about the rotor center. This is an improvement of the earlier quasi-steady flow model of Colding-Jorgensen (1980) where the impeller was taken as a single vortex source point. The forces can be presente d as a sum of a steady and an unsteady part. The rotordynamic coeffici ents are deduced from the unsteady forces decomposed into radial and t angential components relative to the orbit described by the impeller c enter. in comparison to most of the theoretical and experimental resul ts found in the literature, the model seems to give good prediction. I t appears clearly from this analysis that, under certain operating con ditions, the fluid forces on the impeller have a destabilizing effect on the pump rotor.