## 3 Prototype Performance Analysis  
The vibration characteristics of a typical fan used in nuclear power generation cannot be ignored during its own operation. Strong vibrations can subject rotating machinery to additional unfavourable loads, generate huge noise, and, in severe cases, even cause extreme consequences such as equipment failure, endangering the operational safety of nuclear power plants. At the same time, as the axial flow fan works, the irregular flow and vibration phenomenon caused by the structural design destroys the flow energy and leads to pressure pulsation between the blades and the flow channel, especially in the inflow area of the guide vane, resulting in energy loss and waste under working conditions, thus affecting the stability and safety of the equipment work [1]. Therefore, the simulation and analysis of the vibration characteristics and aerodynamic properties of the critical \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \(\boldsymbol{Q}\) (m\({}^{3}\)/h) & **40,516.5** & **57,319.8** & **65,316.5** & **67,684.8** & **70,263.1** & **73,718.2** & **77,661.4** & **81,414.0** & **84,769.2** \\ \hline Simulated value (dB) & 107.7 & 109.4 & 109.9 & 110.2 & 109.5 & 109.4 & 109.8 & 109.5 & 109.4 \\ Experimental value (dB) & 108.5 & 110.3 & 110.8 & 110.9 & 110.4 & 110.3 & 110.5 & 110.6 & 111.2 \\ Difference (\%) & 0.74 & 0.82 & 0.81 & 0.63 & 0.82 & 0.81 & 0.63 & 0.99 & 0.72 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of test and simulation under different working conditions. Figure 7: Noise test device. parts of the fan are of direct importance for the optimisation of pressure pulsation in practical engineering. To obtain primary data on the vibration characteristics of the fan's essential parts and identify the vibration- and noise-inducing mechanisms, corresponding experimental studies are required. The frequency domain data are acquired by the B&K Time Data Recorder software and the B&K 4535-B triaxial acceleration sensors are used for the vibration signal acquisition during the operation of the nuclear grade axial flow fan. As shown in Figure 8a, the measurement points were installed with triaxial acceleration sensors in the OGVs duct, dynamic-static coupling duct, and rotation duct. The B&K 4535-B triaxial accelerometer is shown in Figure 8b. As shown in Figure 9, according to the analysis of the test data, the triaxial acceleration of the fan showed significant fluctuations from 0 to 250 Hz and 450 to 600 Hz in the 0 to 600 Hz band in the OGVs duct, dynamic-static coupling duct, and rotation duct near the motor. The radial acceleration fluctuates the most, while the remaining two fluctuate less. In addition, the fluctuations in radial acceleration in the 0-600 Hz band in the static lobe region are generally more significant than those in the remaining two areas, especially in the 450-600 Hz range, which is presumed to be caused by the vibration of the fluid passing through the OGVs duct. To get a clearer view of the internal flow field characteristics of the axial flow fan, the blade flow surfaces of the fan impeller with radial cross-sections of 0.1, 0.5, and 0.9 span were chosen for the study. Figure 10 shows a schematic diagram of the radial section of the fan impeller. Figure 8: Vibration test equipment. (**a**) Distribution of triaxial acceleration sensors. (**b**) B&K 4535-B triaxial accelerometer. Figure 9: Frequency domain analysis of accelerated vibrations. (**a**) Radical acceleration. (**b**) Axial acceleration. (**c**) Circumferential acceleration.