## 4 Conclusions  
In this paper, OpenFOAM software is used to study the wake of three small wind turbines added to two wind turbines in a series. In addition, we carried out experimental verification in the wind tunnel. The influence of different distances between each row of small wind turbines and the upstream large wind turbines on the power of the downstream  
Figure 9: The effect of the change in the position of the small wind turbine on the wind speed from the large downstream wind turbine at \(Z=150\) m.  
wind turbines is studied. After analyzing the vertical velocity wind profile and regional flow field, the following conclusions are obtained:  
1. Small wind turbines with different distances have an impact on the power output of downstream wind turbines. The power of the downstream large wind turbine increases by about 0.5% when the small and large wind turbines are \(2D+15d\) away from the upstream large wind turbines, as in Case 4. The wind tunnel experiment results also show that the power of the downstream large wind turbine increases by 0.69%..
2. At the height of the small wind turbine, the velocity distribution of the wake obviously attenuates, and this attenuation will weaken as it moves downstream; however, the wind speed at the higher position of the small wind turbine will increase, and this increase effect will be captured by the adjacent downstream large wind turbine, resulting in an increase in the output power of the downstream large wind turbine. Conceptualization, S.K. ; methodology, J.W. ; formal analysis, H.T. ; Writing--original draft preparation, W.T. ; writing--review and editing, W.T. and Y.Z. ; visualization, X.Z. ; supervision, S.K. ; project administration, W.T. ; funding acquisition, S.K. and L.Z. ; wind tunnel test, S.W. ; verification, L.Z. and S.W. All authors have read and agreed to the published version of the manuscript. This work was funded by the Jilin Provincial Science and Technology Department of Science and Technology Key Research and Development Projects (Grant number 20200403141 SF) and the Open Project of State Key Laboratory (Grant number D2020Y004-3, HB2021Y003). National key red program (Grant number 2019 YFB1503701), National Natural Science Foundation of China (Grant number 52078251, 52108456), Jiangsu Outstanding Youth Science Fund Project (Grant number BK20211518), Jiangsu Natural Science Foundation (Grant number BK20210309) and The Fundamental Research Funds for the Central Universities through grant no (Grant number NS20201050, NE2020007). Not applicable. Note applicable. * [PERSON] and [PERSON] (2019) [PERSON]; [PERSON] [PERSON] A ring-vortex actuator disk method for wind turbines including hub effects. _Energy Convers. Manag._**2019**, _195_, 672-681. [CrossRef]
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