## 3 Results and Discussions
### Velocity Field Distribution under Different Operating Conditions  
We compare the power change caused by the downstream wind turbine under the influence of the small wind turbine's wake, as shown in Figures 8 and 9. Figure 8 shows the influence of the wake of the small wind turbine on the flow field near the downstream wind turbine under different working conditions; Figure 9 shows the change in the vertical velocity wind profile of the flow field in front of the downstream wind turbine.  
A comprehensive comparison between Case 1-4 and Case 0 shows that the small wind turbine plays a certain role in improving the airflow, and its principle is similar to the deflector of vertical axis wind turbines [32]. As can be seen by the position of the white arrow in case 1 in Figure 8, as the small wind turbine gradually approaches the downstream large wind turbine, the air flow lifting effect generated by it gradually increases. This strengthening effect can be understood as: when there are certain obstacles in front of the wind turbine, the air flow lifting effect generated by it can better improve the incoming speed of the wind turbine [33], while when the distance is long, this air flow lifting effect is very small, resulting in the negative impact of the turbulent wake of the small wind turbine taking the dominant position.  
Figure 7: Comparison of vertical velocity wind profiles of Case 4 and Case 0.  
Figure 8: Streamwise mean velocity in the YZ and XZ planes. (**a**) Case 0. (**b**) Case 1. (**c**) Case 2. (**d**) Case 3. (**e**) Case 4.  
It can be seen from Figure 8 that as the small wind turbine gradually approaches the downstream wind turbine, the vertical velocity of the flow field in front of the wind turbine is increased. From the quantitative results in Figure 8, it can be seen that Case 4 condition has the largest increase in the speed in front of the downstream wind turbine, about 0.793%.  
According to Figure 9, it is easy to see that as the small wind turbine gradually moves downstream, the wind speed at the center of the hub of the large downstream wind turbine gradually increases.  
When the small wind turbine is far away from the large downstream wind turbine (Case 1, Case 2), the incoming wind speed at the hub of the large downstream wind turbine decreases slightly compared to Case 0 (\(u=8.85\) m/s \(\to u=8.82\) m/s) due to the influence of the small wind turbine. Taking Case 1 as an example, due to its distance from the large downstream wind turbine, the wake of the three small wind turbines is fully developed. As the small wind turbines gradually approach the large wind turbines downstream, the wake of the small wind turbines becomes fully developed before they offset each other, and this offsetting effect gradually increases, resulting in the lifting effect of the small wind turbines.  
In contrast, when the small wind turbine is closer to the large downstream wind turbine, the incoming wind speed at the center of the hub of the large downstream wind turbine has a certain increase effect compared with Case 0 (\(u=8.85\) m/s \(\to u=8.88\) m/s). Take Case 4 as an example: because the small wind turbine is closer to the downstream large wind turbine, the wake flows cancel each other more fully, and the wind speed at the center of the downstream large wind turbine hub is promoted by the lifting effect of the airflow of the small wind turbine.