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.

针对环境问题和防灾问题，从植被流体动力学角度分析林冠层防风功能的机理具有重要意义。本研究进行了湍流风洞试验和拖曳风洞试验两类试验。前一试验表明，森林冠层模型的叶片指数对模型下游流场的影响。后一试验结果表明，采油树在导道中进行拖曳，并测量了采油树下游的流场。主要结论总结如下。30cm高度冠层模型的叶面积指数变化很大，从极为稀疏的模型1.8到热带雨林的9。在10m/s风速的均匀流动中，利用CTA测量了模型下游的平均流速和湍流强度分布。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。而对于湍流强度，叶面积指数的影响有所增强。这些效应在冠层模型的冠层下游区域尤为显著。用CTA在真树的下游用拖曳风洞测量了流场。该树为针叶树，高2米，最大直径80cm。树以10m/s的速度牵引。在树的最大直径部分的直接下游，速度缺陷率约为85%。然而，在树高的两倍的下游，速度缺陷率下降到30%左右。高速缺陷率区域的湍流强度约为10%。在树尾边缘，湍流强度为30% - 40%。湍流能量的产生与平均速度分布的快速梯度有关。