Influence of rotation speed on flow field and hydraulic noise in the conduit of a vertical axial-flow pump under low flow rate condition

The complex flow inside the axial-flow pump device will cause the problem of hydraulic noise, in order to explore the influence law of rotation speed on the internal flow characteristics and hydraulic noise of the axial-flow pump conduit, the combination of Computational Fluid Dynamics (CFD) and Computational Acoustics (CA) is used to numerically solve the flow field and internal sound field in the pump device. The results show that the flow in the elbow inlet conduit is smooth at different rotation speeds, and there is no obvious unstable flow. The higher the rotation speed, the more disordered the flow pattern in the left half of the elbow, which intensifies the unstable flow in the straight outlet conduit. The impeller is the main sound source of the internal hydrodynamic noise of the vertical axial-flow pump device, when the sound source propagates upstream and downstream along the conduit, the Total Sound Source Intensity (TSSI) will gradually decay with the increase of distance, the greater the rotation speed is, the faster the Total Sound Source Intensity (TSSI) will decay. When the rotation speed is increased from 1450 r/min to 2200 r/min, the TSSI in the straight outlet conduit is attenuated by 8.9 dB, 13.9 dB and 16.0 dB respectively, and the TSSI in the elbow inlet conduit is attenuated by 11.0 dB, 13.5 dB and 25.9 dB respectively. The vortex structure in the conduit will induce flow noise and delay the attenuation of TSSI in the propagation process, with the increase of rotation speed, this delay will be more obvious.