# Wind Field Characteristics of Complex Terrain Based on Experimental and Numerical Investigation
## 4 Numerical Simulation Results  
### Determination of Control Wind Direction  
In order to deeply explore the wind field of the model by the wind tunnel test, a variety of inflow directions are used in the numerical simulation. Due to the geographical location of the island, the sea breeze often comes from the east of the island. In view of the above characteristics, the simulated working conditions focus on the incoming flow from the east, as shown in Figure 6.  
The hub height of most wind turbines is 104 m, so the wind speed at 104 m of each measuring point in the simulation results is statistically analyzed. Specifically, the dimensionless wind speed of each measuring point at a specific height under different wind directions is sorted. The two highest wind speeds are selected as the control wind speed, and the results of each incoming flow are shown in Figure 7. It can be seen from Figure 6 that the number of control wind speeds under 90\({}^{\circ}\) and 270\({}^{\circ}\) inflow is the largest, while there is no control wind speed at each measuring point under 20\({}^{\circ}\) inflow. The wind speed is closely related to the location of the measuring point. The incoming flow entering  
Figure 5: (**a**) The island terrain model in wind tunnel; (**b**) the Cobra probe.  
from different directions will be disturbed by the different terrain. Therefore, the wind speed at the same measuring point under different incoming flows will also change greatly. The most common wind direction of the island is 40\({}^{\circ}\), so this paper selects 40\({}^{\circ}\), 90\({}^{\circ}\) and 270\({}^{\circ}\) as the control wind direction for further research. The highest point was chosen as an example to illustrate this result. Figure 8 shows the vertical velocity cloud map of a mountain top measuring point (S, Red line) under the inflow of 20\({}^{\circ}\), 40\({}^{\circ}\), 90\({}^{\circ}\) and 270\({}^{\circ}\). The normal of each section is perpendicular to the inflow. The streamline diagram of each incoming flow is shown in Figure 9.  
As shown in Figure 8, the acceleration effect occurs at vertex s under four wind directions, but the speed of S is different. The velocity of s measuring point is the smallest under 20\({}^{\circ}\) inflow, and the acceleration along the height direction is not as obvious as other incoming flows. It can be seen from Figure 8a that the incoming flow will pass through a valley before reaching points, where it turns around with low wind speed, and then continues to advance along the hillside to points. Compared with the 40\({}^{\circ}\) inflow in Figure 8b, the acceleration distance of 20\({}^{\circ}\) is shorter, so the wind speed is smaller. When the inflow enters the island from 90\({}^{\circ}\) and 270\({}^{\circ}\), the forward process is relatively flat and not greatly affected, so the wind speed is large.  
Figure 6: Different inflow conditions of numerical simulation.  
Figure 7: Quantity of capture wind speed under each incoming flow.  
From the above analysis, it can be seen that when the incoming flow enters the island from 90\({}^{\circ}\) and 270\({}^{\circ}\), the forward process is relatively flat and not greatly affected, so the wind speed is large. The only large valley on the island strikes from north to south, which is consistent with the two incoming flow directions. On the whole, other inflow directions are greatly affected, and even spiral airflow appears. Therefore, from the wind speed analysis, the control wind direction is 90\({}^{\circ}\) and 270\({}^{\circ}\). In addition, considering that the most common wind direction in reality is 40\({}^{\circ}\). The incoming flow of subsequent wind tunnel tests adopts the above three wind directions.