Numerical and Experimental Investigation on the Unsteady Flow Field and Noise Generation in a Centrifugal Pump Impeller

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 on 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. A pump fitted with a vaneless diffuser and a return channel was used as the test model. Flow velocity was measured in pump and diffuser inflow, to establish a link between the flow field structure and acoustic radiation. Results showed that 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. Periodic fluctuations at the discharge of the impeller were seen as a result of this instability. Fluctuations were found to be coherent from blade to blade, and to possess a rich harmonic content. The pressure frequency scattering by the pump was found to be consistent when compared to the experimental and analytic results, but not for the total pressure in the far field.