Extensive research on centrifugal pumps was designed to investigate the impact of a diffuser on flow field instabilities and the noise generated by these instabilities. Activity was based upon a coupled use of measurements and 3D fully-viscous, unsteady computations. The test model was a seven-blade pump-turbine, used as a pump. Fitted with a vaneless diffuser, and two vaned diffusers with twenty-two adjustable, guide-diffuser vanes, and a return channel with eleven continuous vanes. Diffusers were equipped with eight pressure sensors in the adjustable guide-diffuser vanes, and nineteen pressure taps in the continuous vanes. To establish a link between the flow field structure and acoustic radiation, flow velocity was measured in the vaneless part of the diffuser. Piezoelectric transducers, placed flush with the wall, were used to measure pressure fluctuation inside the blade channels. Signal analysis was carried out in the frequency domain. Results showed the jet-wake flow pattern induced an unstable vortex, which influenced flow discharging from the adjacent passage, and destabilized jet-wake flow in the passage. This instability caused a periodic fluctuation at the discharge of the impeller. Fluctuations were found to be coherent from blade to blade, and to possess a rich harmonic content. Numerical analyses did not fully confirm these results.

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