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.

The development of low-noise pumps is essential to design quiet fluid delivery systems. Due to the complicated internal flow, the flow-induced noise characteristics of high-speed centrifugal pumps have not been well understood. Taking engine cooling pumps as an example model, experimental measurements are performed in a semi-anechoic room and a CFD/CFA calculation method is proposed to study the fluid-borne noise and radiated noise characteristics. In the speed range of 5000–6750 r/min, both the pump head and the dimensionless radiated noise characteristics conform to similar laws, and the highest efficiency point pump presents the lowest noise level. Consistent with the experimental results, the predicted radiated noise of the model pump presents dipole characteristics at the required flow rate condition. Moreover, the spectrum of fluid borne noise at pump outlet shows broadband characteristics but with obvious discrete peaks, which are not only related to the fluid pressure pulsation characteristics (6f0 and the multiple) at the low-frequency region, but also to the frequency of the structural mode (3000–6000 Hz region). Rotor-stator interaction of the pump flow field between the impeller and volute is the main reason of flow-induced noise; unstable flow also contributes to the broadband components in the noise spectrum.

Cooling pump is an important device to ensure the reliable and stable working of the internal combustion engine. As the size of the structure is limited by space, its internal flow is complex. To explore the internal flow of cooling pump, the numerical simulation of the full flow field of the model pump under different flow conditions is carried out by using the Detached-Eddy Simulation (DES) model, and the unstable flow characteristics in the flow-path are analyzed. The results show that the intensity of pressure fluctuation near the tongue is the highest and the flow deterioration is the most serious. Under the condition of small flow rate, the area of flow separation is from the tongue to the outlet, return vortices and rotating stall occur in the impeller flow-path, and the outlet vortices dominate the vibration characteristics of the cooling pump. The lowest non-uniformity coefficient of impeller inlet corresponds to the 0.7Q d working point in high efficiency area, but the vertical degree of outflow is same, which is close to the ideal flow direction, and the velocity distribution of flow-path section becomes more uniform with the increase of flow rate. The change of flow rate will affect the unstable degree of the inlet flow, thus affecting the flow rate of the working fluid flowing into the impeller. The unstable degree of the inlet is more serious when the cooling pump works under the condition of small flow rate. The research results can provide some theoretical reference for the structural design of cooling pump.

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