LES study on the influence of the diffuser inlet angle of a centrifugal pump on pressure fluctuations

Large-Eddy Simulations are conducted on a centrifugal pump at design and reduced flow-rates for three diffuser geometries, to investigate the effect of changing the diffuser inlet angle on the overall performance and the pressure fields. In particular, pressure fluctuations are investigated, which affect the unsteady loads acting on the pump, as well as vibrations, noise and cavitation phenomena. The considered modification of the diffuser geometry is targeted at decreasing the incidence angle at the off-design flow-rate by rotating the stationary blades of the pump around their leading edge. Results are compared against those of an earlier study, where the same modification of the diffuser inlet angle was achieved by increasing also the radial gap between impeller and diffuser, whose blades were rotated relative to their mid camber location. The comparisons across cases demonstrate that the radial gap between the trailing edge of the impeller blades and the leading edge of the diffuser blades has a more profound influence on pressure fluctuations, compared to the angle of incidence on the diffuser blades of the flow coming from the impeller.