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

2002 Fiscal Year Final Research Report Summary

• Project/Area Number: 13650188
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Fluid engineering
• Research Institution: MIYAZAKI UNIVERSITY
• Principal Investigator: HIRANO Kimitaka Miyazaki University, Department of Mechanical Systems Engineering, Professor, 工学部, 教授 (40094081)
• Project Period (FY): 2001 – 2002
• Keywords: forest canopy / turbulent wind tunnel / towing wind tunnel / effect of wind break / turbulent energy / leaf area index

Research Abstract

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.