Analysis of noise source in a centrifugal pump based on vortex sound theory

Although various structural modifications of the impeller and volute are employed to suppress flow-induced noise, few such modifications focus on the relationship between the generation and the variation of flow and noise. Herein, the spatiotemporal evolution of vortex structure and noise source in impeller and volute is investigated by vortex sound theory and spectral proper orthogonal decomposition (sPOD). The results show that the tip leakage vortex (TLV) formed near the blade leading edge is a significant noise source. As the TLV develops into a passage vortex, the strength of noise source gradually decreases. Within the passage, the noise source at 90% span attenuates because of the interaction between shed vortices, whereas the noise at 50% span is due to the spatial interaction of noise source. Furthermore, the variation of entropy production correlates with noise source. In the near-tongue region, the dominant rotation frequency and second blade passing frequency (2BPF) are obtained by sPOD, which reveals that the jet wake is extracted at 2BPF and flow patterns featuring strip-like structures appear. Correspondingly, the noise source forms a multiscale dotted distribution near the blade trailing edge (BTE). In comparison with original BTE, the wavy BTE effectively suppresses the multiscale pattern of noise source generated from the BTE at rotation frequency and 2BPF, with a decrease in about 20.75% and 8.35% in the total energy of the two leading modes. However, the characteristics of noise source near the tongue remain unchanged. These findings provide meaningful insights into the noise reduction of centrifugal pump.