A FINITE ELEMENT PERTURBATION METHOD FOR COMPUTING FLUID-INDUCED FORCES ON A CENTRIFUGAL IMPELLER ROTATING AND WHIRLING IN A VOLUTE CASING

A nite element based method has been developed for computing time-averaged uid-induced radial exci- tation forces and rotor dynamic forces on a two-dimensional centrifugal impeller rotating and whirling in a volute casing. In this method potential ow theory is used, which implies the assumption of irrotational in- viscid ow. In comparison with other analyses of uid-induced impeller forces, two main features have been included. Firstly, the hydrodynamic interaction between impeller and volute is properly modelled. Secondly, the variation of the width of the volute has been adequately included in the two-dimensional analysis by a modi cation of the equation of continuity. A regular perturbation method is used to deal with the e ects of the whirling motion of the impeller. The excitation forces are calculated from the zeroth-order problem in which the impeller axis is placed at the volute origin. The rotor dynamic forces associated with the whirling motion of the impeller are derived from the rst-order solution. The force components, tangential and normal to the whirl orbit, are predicted as functions of the impeller{volute geometry, the ow condi- tions and the whirl speed ratio. The method is applied to a centrifugal pump experimentally tested at the California Institute of Technology. Comparisons between predictions and experimental data show the capa- bilities of the proposed method to reproduce the main features of uid-induced impeller forces in centrifugal pump