## 4 Results and Discussion
### Influence of Turbulence Intensity on Aerodynamic Performance of Wind Turbines
#### 4.2.2 Effect of Turbulence Intensity on Structural Response  
In the turbulent wind field, the unsteady load of fan blades will certainly cause the unsteady characteristics of elastic deformation of fan system blades. For large fan blades, the flexibility of blades is more obvious. Turbulent wind often brings obvious blade deformation, and there may be sudden large deformation in a certain period of time. Therefore, it is very necessary to study blade deformation under turbulent wind conditions. The following Figure shows the corresponding deformation of blades under the conditions of uniform wind and 5%, 10% and 15% turbulence intensity in 20-40 s, respectively. The turbulent wind field corresponding to 5%, 10% and 15% turbulence intensity is set according to the wind field used in Section 4.2. In order to describe the positions of different blades of the wind turbine, the azimuth Angle adopted in this paper is shown in Figure 21. Blade azimuth is defined as 0-degree azimuth of No. 1 blade pointing to 12 o'clock direction and 180-degree azimuth of No. 1 blade pointing to 6 o'clock direction. From Figure 22a, it can be seen that the fan is basically in a normal working condition after 30 s under the effect of uniform wind speed. Throughout the simulation, the blade tip displacement curve is very regular, and the blade tip displacement is kept at a constant value of about 4.78 m, which is consistent with the previous conclusion. Compared with the  
Figure 21: Blade azimuth Angle (From left to right, they are 0 degrees, 60 degrees, 120 degrees and 180 degrees). Figure 20: Flow field distribution comparison of different turbulence intensities at 10 m/s. (**a**) Tail vortex distribution under uniform wind. (**b**) Tail vortex distribution at 5% turbulence intensity. (**c**) Tail vortex distribution at 10% turbulence intensity. (**d**) Tail vortex distribution at 15% turbulence intensity. case of uniform wind in Figure 22a, the blade vibration form has two different changes due to the turbulence influence of wind, and the blade tip flapping displacement is significantly different between 20-30 s and 30-40 s.  
Figure 22: Time-history curve of blade tip displacement under turbulent wind field: **(a)** Uniform wind; **(b)** 5% turbulence intensity (20–30 s); **(c)** 10% turbulence intensity (20–30 s); **(d)** 15% turbulence intensity (20–30 s); **(e)** 5% turbulence intensity (30–40 s); **(f)** 10% turbulence intensity (30–40 s); **(g)** 15% turbulence intensity (30–40 s). As shown in Figure 22b-g, by analyzing the different blade tip displacements of the same wind turbine, it can be seen that the blade is mainly affected by the shear wind within 20-30 s. When the blade is located at 0-degree angle of azimuth, the blade tip is located at the highest point of the whole wind wheel, the wind speed is the largest at this moment, and the blade displacement is also the largest. After about 2.55 s, the blade runs to 180-degree angle of azimuth, where the wind speed is the lowest and the blade displacement is the smallest. Then, the tip displacement of the three blades was extracted, and the tip displacement curve of the three blades changed with the change of blade azimuth. The deformation forms of the three blades were basically the same, but there was a phase difference of 120\({}^{\circ}\) between them. In 30-40 s, from the velocity field and pressure field around the three blades at the same time, the blade at this moment in the turbulent wind by the local gust of wind, the blade a region of the load suddenly increased, resulting in irregular displacement changes of the blade. The blade tip often appears irregular great deformation, it is extremely convenient to lead to the fatigue damage of the material in the region, also may lead to the delamination and mutual separation between the composite materials, is not conducive to the structural safety of the blade. The flapping deformation of the blade tip within 20-40 s was selected for analysis.