摘 要

近年来，随着全球气候变化频繁，台风极端灾害性天气发生频率和风力强度日益加剧，森林作为环境系统重要的组成部分，正遭受到了巨大的损害。台风的巨大水平力和树身重量相互作用于林木，使得树木风倒频繁发生。因此研究树木的抗风特性有着重要的意义。本文使用计算机仿真模拟的数值模拟方法对流场在林分中的运动进行分析，主要方法如下：首先通过GAMBIT对三维的树冠进行树木建模并进行网格划分，其次使用标准k-epsilon方程组对三维树冠的流场分布进行模拟。最后通过模拟计算所得的树冠周围压力场的分布、风速的分布、湍动能分布与其他学者的模拟研究成果和实验数据进行交叉对比。结果表明：对于单株树，当树冠孔隙度从0.25变化到0.75，即叶面积指数LAI从2.773变化到0.575时，冠内风速在树冠内的波动幅度从8m/s下降到4m/s，树冠内压力的波动幅度从229pa下降到到143.5pa，湍流强度的波动幅度从6.03%降到3.4%；对于林冠来说，当孔隙度从0.25变化到0.75，即叶面积指数LAI从2.773变化到0.575时，风在林冠前后的风速差变化为17.67m/s到15.89m/s，压力差从180.38pa变化到117.38pa，湍流强度的变化幅度从4%变化到2.4%。由于树冠前后压差过大和树冠内风速差过大会导致树的结构遭到破坏，可以看出越稀疏的林冠，抗风性能越好

关键词：叶团簇；模拟；流场分布；FLUENT

ABSTRACT

In recent years, with the frequent changes in global climate, the frequency and intensity of extreme weather of typhoons have intensified. As an important part of the environmental system, forests are suffering tremendous damage. The typhoon's enormous horizontal force and tree body weight interact with the trees, causing the trees to fall frequently. Therefore, it is of great significance to study the wind resistance of trees. In this paper, the computer-simulated numerical simulation method is used to analyze the movement of the flow field in the forest. The main methods are as follows: Firstly, the trees of the three-dimensional canopy are modeled and meshed by GAMBIT, and then the standard k-epsilon equations are used. The flow field distribution of the three-dimensional canopy was simulated. Finally, the distribution of the pressure field around the tree canopy, the distribution of wind speed, and the distribution of turbulent kinetic energy are compared with other scholars' simulation research results and experimental data. The results show that for a single tree, when the crown's porosity changes from 0.25 to 0.75, that is, the leaf area index LAI varies from 2.773 to 0.575, the intra-canopy wind speed fluctuation within the canopy decreases from 8m/s to 4m/s. The fluctuation range of the internal pressure dropped from 229 to 143.5pa, and the fluctuation amplitude of turbulence intensity dropped from 6.03% to 3.4%. For the canopy, when the porosity changed from 0.25 to 0.75, the LAI changed from 2.773 to 0.575. At the time, the wind speed difference before and after canopy change was 17.67m/s to 15.89m/s, the pressure difference was changed from 180.38pa to 117.38pa, and the change range of turbulence intensity was changed from 4% to 2.4%. As the pressure difference between the front and the back of the crown is too large and the wind speed difference in the canopy is too large to cause the structure of the tree to be destroyed, it can be seen that the more sparse canopy, the better the wind resistance performance.

Key words: canopy;simulationl; flow field distribution;FLUENT

目 录

1. 绪论……………………………………………………………………5
2. 问题的提出………………………………………….…………………………………...5
3. 本课题的主要研究内容…………………………………………………………………7
4. 模拟方法研究……………………………………………………………………8
5. 计算流体力学基础知识…………………………………………………………………8
6. k-epsilon模型介绍…………………………………………………………………….9
7. 主要使用软件介绍……………………………………………………………………..12
8. 叶团簇内外流场分析…………………………………………………………14
9. 叶团簇模型及边界条件………………………………………………………………..14
10. 模型计算………………………………………………………………………………..18
11. 数据分析………………………………………………………………………………..20
12. 结论与展望……………………………………………………………………26
13. 本课题的研究结论……………………………………………………………………26
14. 前景展望与建议………………………………………………………………………26

致谢…………………………………………………………………………………………27

参考文献…………………………………………………………………………………...28

1. 绪论
2. 问题的提出

风作为森林生态系统中最有害的干扰因素。近年来，大陆尺度的扰动频率和被扰动严重程度一直在增加，预计未来气候在人为的干涉下，这种趋势会持续下去。至少在过去数十年至数百年间，风力扰动一直是这些生态系统的特征^[1]。正是由于风灾对世界各地的森林植被与生态环境产生了极大的破坏。近年来，世界各地的学者都开展了针对树木风灾成因与林分在强风力载荷下的安全性评估的研究。主要分为如下三类。

一、采用物理学装置来分析树木在风力载荷下的形变受力。如在树木根部的主干处安置动态倾斜的响应装置^[2][3]检测树干外层纤维的线性应变，通过常年的参数记录分析出对树体产生的倾斜力对树木稳定性的影响，或通过固定在树木主枝干上的应变传感器来分析风载荷下的主枝干的位移与应变力之间的关系^[4]；或者通过对真实树体的牵引试验和模拟树木倾覆过程 来分析不同 的土壤类型和树的根部面积对树木的稳定性作用，同时从树的拉伸试验中分析 树木的最大倾覆力以及土壤的抗剪强度; 也有学者采用超声波风速计搭载三维双轴 倾角传感器测量了风载下树冠内不同空间的摇摆与震动频率，推测高 阶振动模式与风激励效应的关联性; 也有学者研究采用多重调谐质量阻尼器的安置^[5] 分析树体的风振效应；或在树冠中放置三维磁化跟踪器^[5]来述和量化风力诱发下的林木复杂运动，结合冠内枝叶的不同密度、风速，用于建立植物与风的相互作用力下的评估模型。