Effect of circumferential outlet distortion on the flow characteristics at the impeller exit of a centrifugal pump

Abstract

Abstract

Centrifugal impellers are exposed to downstream circumferential outlet distortions due to non-axisymmetric volutes or diffusers. This paper explores the effect of circumferential outlet distortion on the flow characteristics at the impeller exit of a centrifugal pump. A fence with non-uniform height was installed at the vaneless diffuser exit to create the outlet distortion, and then unsteady velocity and static pressure were measured at the impeller exit. The instantaneous and mean flow fields at the impeller exit varied with the circumferential position. Plots of the flows against the local flowrate showed hysteretic loops that deviated from the quasi-steady curves obtained from the flows without the fence. When the assumption of quasi-steady variation was applied to the present impeller-diffuser interaction, the prediction for the total and static pressure was reasonable but showed a phase difference for the absolute velocity.