A study of rotating stall in a vaneless diffuser of radial flow pump

Abstract

Rotating stall in a vaneless diffuser of radial flow pump is studied. The measurements consist of: (i) unsteady pressure measurements delivered by two microphones; and (ii) nine steady pressure taps mounted in one radial line to measure the pressure recovery in the vaneless diffuser. Spectrum analysis was used to identify and characterize rotating stall. An assumption was made to estimate the losses in the vaneless diffuser to evaluate the effect of the instability development on its performance. The result has shown that the arising of rotating stall has a positive effect on the diffuser performance. Two possible reasons are proposed: (1) a blockage in the diffuser due to the unstable cells which shortens the streamlines and decreased the friction losses along the vaneless diffuser; (2) the topology of rotating stall cells results in the convection of fluid coming from outside part of the pump model to the vaneless diffuser.