# Numerical Study on Tree Belt Impact on Wind Shear on Agricultural Land
## 4 Discussion  
This study revealed the complex interaction between tree belts and wind airflow, providing valuable guidance for agricultural and energy applications. The deviations in the velocity airfield induced by the tree belts extended significantly downstream. Vertical velocity profiles showed a key pattern: air velocity was lower below \(z\approx 1.5\) h immediately downstream of the belt, while it increased above this height, \(z>1.5\) h, in a range of locations that depended on the belt porosity, ranging from \(x=(1\)-\(4)\) h to \(x=(1~{}+~{}50)\) h. This acceleration, as a result of the conservation-of-mass law, implies a compensation of the blocked airflow across the belt, which is consistent with the authors' observations in [89] of similar compensatory effects in agricultural landscapes.  
The increase in airflow velocity over the belt is consistent with the findings of the authors in [31], who reported air acceleration over porous vegetation barriers. However, the presented study is supplemented with a quantitative analysis, showing that placing turbines above \(z>1.5\) h and near the belt can maximize their efficiency. However, care should be taken about excessive turbulence, which arises with higher-porosity drag coefficients. The total flow analysis revealed a 10% flow rate loss in the upper part of the domain, similar  
Figure 9: Velocity profiles at locations normalized with the tree belt height for the porosity coefficient 0.5 m\({}^{-1}\).  
to the observations in [90], but also demonstrated that redistributed velocity over the belt concentrated the energy, which can improve the performance of the turbines.  
In terms of turbulence, the study identified the shear layer up to 1.5 h as the main source of turbulence. In agreement with findings in [91], the present findings showed that drag coefficients around 0.5 m\({}^{-1}\) had a significant impact on the wake characteristics compared to lower-porosity drag, highlighting the differences in effects between porous and non-porous barriers.  
The study showed that wind turbines located above \(z>1.5\) h can benefit from the increased wind speed; however, to completely avoid induced turbulence effects near the belt, one may want to target elevations of 2.5 h and above. This recommendation builds on the work of the authors in [92], who stressed the importance of rotor positioning relative to turbulent zones. Also, reducing downstream turbulence implies less impact on turbines if they are located in these zones.  
The relatively realistic belt geometry and physically correct boundary conditions, coupled with the robust model of porosity drag, provide a solid foundation for understanding the interactions between vegetation barriers and wind airflow. Future research can build on this approach by incorporating a diversity of vegetation types, even further seasonal variation (manifested by the porosity drag coefficient), and field validations to extend the applicability of results to real-world environments. In addition, integrating rotor dynamics and material fatigue models, as proposed in [93], will contribute to a more complete understanding of the long-term effects of turbulence on turbine durability and efficiency.  
These findings are particularly relevant for rural energy planning and microgeneration systems. The observed flow acceleration above the tree belts and the turbulence patterns suggest that careful vertical positioning of wind turbines can lead to significant performance gains. In practice, placing turbines above the turbulence-affected zone (typically above 2.5 times the belt height) allows for better exploitation of the accelerated flow while minimizing structural loads caused by turbulent eddies. Moreover, the insensitivity of results beyond a porosity of 0.5 m\({}^{-1}\) indicates that extremely dense belts may not be cost-effective or necessary for aerodynamic optimization.