Research on the Windbreak Function of Forest Canopies under Strong Wind Flows with the Turbulent Wind Tunnel and the Towing Wind Tunnel

湍流风洞与拖曳风洞强风流下森林冠层防风功能研究

• 批准号: 13650188
• 负责人: HIRANO Kimitaka
• 金额: $ 0.77万
• 依托单位: MIYAZAKI UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650188/
• 关键词: forest canopy; turbulent wind tunnel; towing wind tunnel; effect of wind break; turbulent energy; leaf area index; 植生流体力学; 防風機能; エキネルギー減退; 風洞実験; 環境流体力学; エネルギー減衰

For environmental issues and disaster prevention problems, it is very important to analyze the mechanism of windbreak function of the forest canopy with the vegetation fluid dynamics. In this research two types of experiments are made with the turbulent wind tunnel testing and the towing wind tunnel testing. The former testing shows the effects of the leaf are index of forest canopy models on the flow fields at the downstream of the models. The latter testing shows that the tree is towing in the guide way and flow fields at the downstream of the tree are measured. The summary of main conclusion is as follows.The leaf area indexes of canopy models with 30cm height are widely changed from 1.8 as a more extremely sparse model to 9 as the tropical rainforest. In the uniform flow of 10m/s wind velocity, distributions of mean velocity and turbulence intensity of flows are measured at downstream of the models with the CTA. For the forest models that the leaf area indexes are over 3, mean velocity distributions are less changed. However, for the turbulence intensity the effects of the leaf area index are increased. Particularly these effects are remarkable in the downstream region of the crown of the canopy models.The flow fields are measured at the downstream of the real tree by the towing wind tunnel with the CTA. The tree is a coniferous tree with the height of 2m and the maximum diameter of 80cm. The tree is towed with the 10m/s speed. The velocity defect rate is about 85% at the immediate downstream of the parts with the maximum diameter of the tree. However, the velocity defect rate decreases to about 30% at the downstream of a double of the tree height. The turbulence intensity in the region of the high velocity defect rate is about 10%. At the edge of the wake of the tree, the turbulence intensity is 30% - 40%. The production of the turbulent energy is made with the rapid gradient of mean velocity distributions.

对于环境问题和防灾问题，利用植被流体动力学分析森林冠层的防风功能机制具有重要意义。本研究进行了湍流风洞试验和拖曳风洞试验两种类型的实验。前次测试表明森林冠层模型的叶指数对模型下游流场的影响。后一测试表明树木在导轨中牵引，并且测量了树木下游的流场。主要结论总结如下。冠层高度为30cm的模型叶面积指数变化较大，从较为稀疏模型的1.8到热带雨林的9。在风速为10m/s的均匀流动中，利用CTA在模型下游测量了流动的平均速度和湍流强度的分布。对于叶面积指数大于3的森林模型，平均速度分布变化较小。然而，对于湍流强度，叶面积指数的影响增加。特别是这些效应在树冠模型树冠的下游区域尤为显着。流场是通过带有 CTA 的牵引风洞在真实树的下游测量的。该树为针叶树，高2m，最大直径80cm。树以10m/s的速度被拖曳。在树木最大直径部分的紧下游，速度缺陷率约为85%。然而，在两倍树高下游，速度缺陷率下降至约 30%。高速缺陷率区域的湍流强度约为10%。在树尾迹边缘，湍流强度为 30% - 40%。湍流能量的产生是通过平均速度分布的快速梯度来实现的。