Non-linear analyses of cavitating flows through a centrifugal impeller by a singularity method.

Abstract

Cavitating flows through a centrifugal impeller were analysed by using a singularity method. The location of cavity surface was determined by an iterative method and the cavity surface boundary conditions were applied exactly on the surface. The closed cavity model of the present calculation gives a thicker face cavity and a thinner back cavity as compared with the results of linear cavity models which assume that the boundary condition can be applied approximately on the vane surface. In case of back cavities, which have smaller thickness, the impeller characteristics are close to those obtained by using the linear cavity model ; higher head was obtained for face cavities. Models assuming a cavity wake with constant displacement thickness or a wake filled with dead water gave significantly lower head compared with that obtained by the closed model. Thus, it was found that, for centrifugal impellers, the cavity wake has a large effect on the characteristics.