Abstract
The radiated noise of the centrifugal pump acts as a disturbance in many applications. The radiated noise is closely related to the hydraulic design. The hydraulic parameters in the multistage pump are complex and the flow interaction among different stages is very strong, which in turn causes vibration and noise problems because of the strong hydraulic excitation. Hence, the mechanism of radiated noise and its relationship with hydraulics must be studied clearly. In order to find the regular pattern of the radiated noise at different operational conditions, a hybrid numerical method was proposed to obtain the flow-induced noise source based on Lighthill acoustic analogy theory, which divided the computational process into two parts: computational fluid dynamics (CFD) and computational acoustics (CA). The unsteady flow field was solved by detached eddy simulation using the commercial CFD code. The detailed flow information near the surface of the vane diffusers and the calculated flow-induced noise source was extracted as the hydraulic exciting force, both of which were used as acoustic sources for radiated noise simulation. The acoustic simulation employed the finite element method code to get the sound pressure level (SPL), frequency response, directivity, et al. results. The experiment was performed inside a semi-anechoic room with a closed type pump test rig. The pump performance and acoustic parameters of the multistage pump at different flow rates were gathered to verify the numerical methods. The computational and experimental results both reveal that the radiated noise exhibits a typical dipole characteristic behavior and its directivity varies with the flowrate. In addition, the sound pressure level (SPL) of the radiated noise fluctuates with the increment of the flow rate and the lowest SPL is generated at 0.8Qd, which corresponds to the maximum efficiency working conditions. Furthermore, the experiment detects that the sound pressure level of the radiated noise in the multistage pump rises linearly with the increase of the rotational speed. Finally, an example of a low noise pump design is processed based on the obtained noise characteristics.
Highlights
Multistage pumps with high pressure are widely used in water supply facilities [1,2,3,4]
Considering that the flow field inside the multistage pump is complex and the acoustic simulation domain is irregular, the finite element method is used in this acoustic simulation which could avoid the inaccuracy during the transformation of the sound source
Apart from the three stages, the is composed of the inlet section, the wear-ring section, pump cavity, impeller, vane diffuser, and the computational stage is composed of the inlet section, the wear-ring section, pump cavity, impeller, outlet section, which are consistent with the flow path of the experimental model pump
Summary
Multistage pumps with high pressure are widely used in water supply facilities [1,2,3,4]. The flow in the multistage pump is highly unsteady and greatly influenced by the interference between the different stages [5,6] These give rise to the pressure pulsations, mechanical vibrations, and the radiated noise in various pump components [7,8,9,10]. A hybrid method that transforms the information of the unsteady flow into the source of the sound is widely used [31,32,33] This method could improve simulation accuracy with lower computational resources [34]. The sound source was extracted from the unsteady computation based on the DES turbulence model, and the simulation code of acoustic finite element method inlaid in software Actran 14 was used to simulate the distribution of the radiated noise of the model pump. The change of the radiated noise with the variation of the flow rate and the rotation speed is discussed
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