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

从植被流体动力学的角度分析林冠层防风作用的机理，对于解决环境问题和防灾问题具有重要意义。本研究进行了紊流风洞试验和拖曳风洞试验两种类型的试验。前一个试验表明了林冠模型的叶面积指数对模型下游流场的影响。后一种试验表明，采油树在导轨中拖曳，测量了采油树下游的流场。主要结论如下：30 cm高度林冠模型的叶面积指数变化幅度较大，从极稀疏模型的1.8到热带雨林的9。在风速为10 m/s的均匀流场中，利用CTA测量了模型下游的平均流速和湍流度分布。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。叶面积指数对湍流度的影响则有所增强。在带有CTA的拖曳式风洞中，对真实的树冠下游的流场进行了测量。树高2米，最大直径80厘米，为针叶树。以10 m/s的速度拖曳采油树。在最大直径处的下游，速度亏损率约为85%。而在两倍树高的下游，速度亏损率降低到30%左右。在高速度缺陷率区域的湍流强度约为10%。在树尾流的边缘，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。

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.