## 1 Introduction
The above research mainly analyzed the influence of the division pier in the outlet conduit through the model test; in recent years, with the rapid development of Computational Fluid Dynamics (CFD), numerical calculation has become an important development direction in the field of pump device research [13, 14, 15], and scholars and engineers in this field have conducted a large amount of research work on the phenomenon of flow deviation in the outlet conduit. In the work by [PERSON] et al. [16], in order to analyze the hydraulic characteristics in the siphon outlet conduit, the numerical simulation method was used to calculate the three-dimensional turbulent flow domain in the siphon outlet conduit under different working conditions. It was found that the outlet flow domain of the guide vane behind the axial-flow pump had an effect on the flow distribution on both sides of the siphon outlet conduit, and the right flow was always greater than the left flow. [PERSON] et al. [7,17] analyzed the outlet conduit and the pump device as a whole system; the CFD method was used to calculate the outlet conduit, and the time domain and frequency spectrum characteristics of velocity fluctuation in the outlet conduit under different working conditions were quantitatively analyzed. It was found that the division pier in the outlet conduit had a great influence on the energy performance of the pump device, reducing the hydraulic performance of the pump device, and the main frequency of velocity fluctuation at each monitoring point of the inlet surface of the outlet conduit under different working conditions was 0.5 times the frequency conversion. In order to study the hydraulic characteristics of the inclined outlet conduit of a large low head pumping station, [PERSON] et al. [18] set up water pressure pulsation measuring points on the left and right sides of the outlet conduit to obtain the pressure of the left and right sides of the flow deviation; combined with a numerical simulation, the causes of the internal flow deviation in the inclined outlet conduit of a \(20^{\circ}\) inclined axial extension pump device were analyzed, and it was found that a large range of vortices were generated in the lower part of the right side of the division pier. When the length of the division pier is 23.35 m, the flow rate on the left and right sides of the inclined outlet conduit is basically the same, the vortex range on the right side of the division pier is gradually reduced, and the pressure values on the left and right sides of the outlet conduit become very close. By means of a model test and numerical simulation, [PERSON] et al. [19; 20] studied the problem of serious flow deviation in the outlet conduit of an inclined axial-flow pump and found that the flow on the left side of the outlet conduit along the flow direction is higher than that on the right side, and the residual circulation has an effect on the flow deviation. It can be seen from the above that a division pier will lead to flow deviation in the outlet conduit, and a certain vortex area will often appear on both sides of the pier [18]; the vortex in the conduit is the main cause of vibration [21]. In the existing research, some scholars have used a Fourier transform to analyze the time domain and frequency domain of pressure fluctuation signals for the phenomenon of flow deviation in the outlet conduit and found that there were a large number of low-frequency signal components on both sides of the division pier in the outlet conduit [22; 23]. However, the most commonly used Fourier transform cannot effectively process the low-frequency signal, and further research on this part of the results to obtain the energy characteristics of the low-frequency signal is of great significance to understand the vibration characteristics of the deflected flow near the division pier or to improve the damage of the flow deviation to the outlet conduit in the future.