## 4 Results
### Pressure Pulsation Analysis  
The numerical simulation of this paper was calculated by FLUENT software, and four monitoring surfaces were set along the overcurrent components; each monitoring surface had four sets of monitoring points, and a total of 16 sets of monitoring data were obtained. Considering that there were many monitoring points, this paper selected only some points for the pressure pulsation analysis. In order to study the distribution of the pressure pulsation along the axial direction, the outer edge points a3, b3, c3, and d3 were selected on the four monitoring surfaces. Figure 9 is the time-domain diagram of the pressure pulsation distribution under different working conditions. In the figure, the pressure pulsation coefficient at the inlet of the runner chamber obviously changed, and its amplitude change was much larger than that at the inlet of the front guide vane and the interface between outlet and guide vane. This indicated that the change in the pressure pulsation was obviously affected by the dynamic and static interference. Figure 9 is the time-domain distribution diagram of the pressure pulsation of each monitoring surface under the working condition of the pump. Because of the dynamic and static interference, the water body flowing into the runner chamber was more violently excited, the pressure pulsation changed more, and the change in the pressure pulsation coefficient at the runner outlet was more severe than that at the outlet of the runner. This demonstrated that although there was static and dynamic interference, the blade rotation greatly influenced  
Figure 8: Comparison of experimental and numerical simulation results. (**i**) Time-domain diagram of the inlet pressure pulsation of pre-guide vanes. (**ii**) Time-domain diagram of the runner inlet pressure pulsation. (**iii**) The frequency domain diagram of the inlet pressure pulsation of the front guide vane. (**iv**) Frequency domain diagram of the runner inlet pressure pulsation. the pressure pulsation; however, the movable guide vane had a good combing effect on the water flow, which greatly reduced the amplitude of the coefficient, improved the flow state, and better converted the kinetic energy of the water flow into pressure energy. The data of the last two result cycles after stabilizing the analysis were selected for analysis. We found that the pressure pulsation exhibited a certain periodic change, especially the pressure pulsation change in the runner area, and there were four peaks and troughs in a single cycle, which was closely related to the number of blades; this fully illustrated the influence of blades on the pressure pulsation. It was not only related to the structure of the flow parts, but also significantly influenced by the rotation of the blades and closely related to the flow rate. When operating under flow conditions, the change in the pressure pulsation with time appeared not only extremely disordered, but also its amplitude of change was much larger than that of the operation under design conditions, indicating that the deviation from design conditions was extremely unstable and prone to occur. Larger pressure pulsation is not conducive to the stable operation of the unit and will also cause different degrees of damage to the overcurrent components. The existence of hydraulic excitation is a hidden danger to the safe operation of the unit. Figure 9: _Cont._  
Figure 10 is a time-domain diagram when the turbine is running. The pressure pulsation changed periodically with time. At the outlet of the runner, there were four peaks and troughs in a single cycle, while at the outlet of the movable guide vane, there were seven peaks and troughs in a single cycle. The number of runner blades was four and the number of movable guide vanes was seven, which indicated that the periodic change in the pressure pulsation was related to the number of blades. In the figure, the amplitude of the pressure pulsation coefficient at the inlet and outlet of the runner was much larger than that at the other two interfaces.