Unsteady flow field and noise generation in a centrifugal pump impeller with a vaneless diffuser

To improve understanding of the phenomena of stall in centrifugal pumps, extensive research was conducted to investigate the impact on flow field instabilities and the noise generated in a pump equipped with a diffuser. A pump fitted with a vaneless diffuser and a return channel was used as the test model. Flow velocity was measured at the pump and at diffuser inflow to establish a link between the flow field structure and acoustic radiation. Activity was based upon the cross spectral analysis of output signals from piezoelectric transducers placed flush with the wall at the inflow and outflow of the pump, and 3D fully-viscous unsteady computations. Results showed the jet-wake flow pattern induced an unstable vortex, which influenced flow discharging from the adjacent passage and, destabilised jet-wake flow in the passage. Consequently, periodic fluctuations were seen at impeller discharge which were found to be coherent from blade to blade and possessed a rich harmonic content. With the exception of the total pressure in the far field, the pressure frequency scattering by the pump was found to be consistent when compared to the experimental and analytic results.