Windproof effect of Robinia pseudoacacia forest in different forest belts
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摘要:
目的 刺槐是我国造林常用树种，在黄河入海口地带广泛种植，但该地区易遭受大风侵袭，刺槐由于根系浅容易发生风倒，因此通过合理的林带布置降低林内最大风速，避免林木倒伏，提升刺槐林的防风效应刻不容缓。 方法 该研究以沿海刺槐防护林为研究对象，基于双向流固耦合技术利用Ansys Workbench平台建立风场与刺槐的计算模型，探讨不同林带结构刺槐林的防风效应。 结果 （1）建立刺槐流固耦合仿真模型，经现场实测数据验证，模型水平归一化风速误差为13%，垂直归一化风速误差为6%，枝干风振位移相对稳定时误差为7 mm，模型具有较高的仿真精度。（2）模拟试验表明首行刺槐对风速减弱的效果明显，在固定行间距5 m的工况下每增加一行刺槐，风速对比前一行刺槐依次降低0.12 $ {v}_{0} $ 、0.07$ {v}_{0} $ 、0.03$ {v}_{0} $ 和0.01$ {v}_{0} $ （$ {v}_{0} $ 为林前初始风速）。（3）相邻的两行刺槐随着行间距的增加，整体防风效果逐渐降低，风经过行间距分别为0.4H、0.5H、0.7H、1.0H和1.5H两行刺槐(H为刺槐树高)，第二行风速分别比第一行减小0.15$ {v}_{0} $ 、0.12$ {v}_{0} $ 、0.07$ {v}_{0} $ 、0.04$ {v}_{0} $ 和0.01$ {v}_{0} $ 。（4）交错排列的刺槐林防风效果优于方形排列，并且交错排列刺槐分枝的风振振幅更小。结论 不同的林带结构对刺槐林的防风效应会产生较大的影响，通过数值模拟技术对不同林带结构的防风效应进行评估是一种有效的研究手段，研究结果能够为该地区后续合理造林提供科学支持。 Abstract:Objective Robinia pseudoacacia is a common used tree species for afforestation in China, which is widely planted in the estuary of the Yellow River. However, the area is vulnerable to strong wind invasion, and Robinia pseudoacacia root is prone to windfall due to its shallow root system. Therefore, a reasonable forest belt layout is of great urgency to reduce the maximum wind speed in the forest, avoid tree collapse and improve the wind-proof effect of Robinia pseudoacacia forest. Method The study focused on the coastal Robinia pseudoacacia shelter forest as the research object. The Ansys Workbench platform was used to establish the calculation model of the wind field and Robinia pseudoacacia based on the two-way fluid-structure coupling technology, so as to discuss the windproof effect of Robinia pseudoacacia forest in different forest belts. Result (1) Establishing the two-way fluid-structure coupling simulation model of Robinia pseudoacacia and the flow field, verified by field test data, the horizontal normalized wind speed error of the model was 13%, and the vertical normalized wind speed error was 6%, and when the wind vibration of the branches was relatively stable, the displacement error was 7 mm, the model had high simulation precision. (2) The simulation results showed that the first row of Robinia pseudoacacia had an obvious effect on reducing the wind speed, under the condition of fixed row spacing of 5 m, for each increased a row of Robinia pseudoacacia, the wind speed was reduced by 0.12 $ {v}_{0} $ , 0.07$ {v}_{0} $ , 0.03$ {v}_{0} $ and 0.01$ {v}_{0} $ ($ {v}_{0} $ was the initial wind speed before the forest). (3) With the increase of row spacing, the overall windproof effect of the two adjacent rows of Robinia pseudoacacia gradually decreased. After the wind passed through the two rows of Robinia pseudoacacia with row spacing of 0.4H, 0.5H, 0.7H, 1.0H and 1.5H, respectively(H is the height of the tree), the difference between the two reduced wind speeds of the two rows of Robinia pseudoacacia was 0.15$ {v}_{0} $ , 0.12$ {v}_{0} $ , 0.07$ {v}_{0} $ , 0.04$ {v}_{0} $ and 0.01$ {v}_{0} $ , respectively. (4) The windbreak effect of staggered Robinia pseudoacacia forests was better than square arrangement, and the wind vibration amplitude of staggered branches of Robinia pseudoacacia was smaller.Conclusion Different forest belt structures have a great influence on the windproof effect of Robinia pseudoacacia forest, it is an effective research method to evaluate the windbreak effect of different forest belt structures by numerical simulation technology, the results can provide scientific support for subsequent reasonable afforestation in this area. -
图 3 实测数据与气象站数据对比图
Figure 3. Comparison of measured data and meteorological station data
图 4 模拟谱与风速谱的比较
Figure 4. Comparison between simulated spectrum and wind speed spectrum
图 5 刺槐与风场双向流固耦合模型示意图
Figure 5. Schematic diagram of two-way fluid-structure coupling between Robinia pseudoacacia and wind field
图 6 水平方向风速归一化对比图
v/v0为归一化风速，即被削弱的风速与初始风速的比值。下同。 v/v0 is the normalized wind speed, i.e, the ratio of the weakened wind speed to the initial wind speed. The same below.
Figure 6. Wind speed comparison in horizontal direction
图 8 刺槐分枝风振位移对比
Figure 8. Comparison of wind-induced displacement of Robinia pseudoacacia branches
图 9 不同行数刺槐的有效防护距离
Figure 9. Effective protection distance of Robinia pseudoacacia with different rows
图 10 不同行数刺槐的归一化风速对比
Figure 10. Comparison of normalized wind speed for different numbers of Robinia pseudoacacia
图 11 不同行间距刺槐的有效防护距离
H为树高，下同。H is tree height, the same below.
Figure 11. Effective protection distance of Robinia pseudoacacia with different row spacing
图 12 不同行间距刺槐的归一化风速对比
Figure 12. Comparison of normalized wind speed of Robinia pseudoacacia with different row spacing
图 13 刺槐X-Y面风速变化云图
Figure 13. Cloud image of wind speed variation on X-Y surface of Robinia pseudoacacia
图 14 两种排列方式下刺槐枝干位移情况
Figure 14. Displacement of Robinia pseudoacacia branches under two arrangements
表 1 刺槐的弹性常数
Table 1. Elastic constant of Robinia pseudoacacia
项目 Project 数值 Numerical value 项目 Project 数值 Numerical value 项目 Project 数值 Numerical value $ {E}_{\mathrm{L}} $ 1.48 × 1010 Pa $ {G}_{\mathrm{L}\mathrm{R}} $ 4.62 × 108 Pa $ {\mu }_{\mathrm{L}\mathrm{R}} $ 0.043 $ {E}_{\mathrm{R}} $ 1.57 × 109 Pa $ {G}_{\mathrm{T}\mathrm{L}} $ 4.47 × 108 Pa $ {\mu }_{\mathrm{R}\mathrm{T}} $ 0.71 $ {E}_{\mathrm{T}} $ 8.04 × 108 Pa $ {G}_{\mathrm{R}\mathrm{T}} $ 1.24 × 108 Pa $ {\mu }_{\mathrm{T}\mathrm{L}} $ 0.029 注：L、R和T分别代表纵向、径向和弦向，E、G和$ \mu $分别代表弹性模量、剪切模量和泊松比。Notes: L, R and T represent longitudina, radial and chord direction, respectively, E, G and $ \mu $ represent elastic modulus, shear modulus and Poisson's ratio, respectively. 
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表 2 双向流固耦合详细设置参数
Table 2. Detailed setting parameters for two-way fluid-structure coupling
项目 Project 参数 Parameter 项目 Project 参数 Parameter 湍流模型
Turbulence model标准k-ε湍流模型
Standard k-ε turbulence model计算时间
Computing time10秒
10 s流体材料
Fluid material25 ℃下模拟生成的风速${v}_{0} $
Wind speed $ {v}_{0} $ generated by simulation at 25 ℃时间步数
Time step number100步
100 steps分析类型
Analysis type瞬态分析
Transient analysis时间步长
Time step0.01秒
0.01 s刺槐模型根部
Robinia pseudoacacia model root固结约束
Fixed support模型网格划分方法
Mesh generation method of model自由网格划分
Free grid division风场四周边界条件
Circumferential boundary conditions of wind field无滑移墙面
No slip wall风场出、入口边界条件
Boundary conditions at the entrance and exit of wind field静态网格移动模式
Static grid movement mode
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