兰州大学机构库 >土木工程与力学学院
防护林风场特征的数值模拟
Alternative TitleNumerical Research of the Characteristics of Wind Field near the Windbreaks
万坤
Thesis Advisor武建军
2017-05-05
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword阻力系数 叶面积密度 防风效果
Abstract

防护林可以对水土保持、防风治沙以及土壤风蚀等起到良好的作用,因此研究防护林的风场特征对于理论与实际都有着重要意义。目前对于防护林风场特性的探讨大部分应用的都是野外观测与实验的方法,虽然也有一部分数值模拟的内容,但主要集中在二维数值模拟。本文以之前的防护林研究内容为基础,讨论了植被阻力系数与其影响因素间的关系,对其准确性进行了验证,并计算了叶面积指数、株间距、行间距、行数及分布方式和冠层宽度等因素对防护林阻风效果的影响。主要研究内容为:1. 详细介绍了植被冠层内部流场的控制方程。基于湍流的时间平均控制方程,对其进行空间平均进而得到植被冠层内部流场的运动方程。并且讨论了控制方程中相关物理量的求解方法以及相关参数的取值。2. 考虑到之前关于植被冠层内部的风场运动的计算均将阻力系数取为定值,然而植被在不同高度上的叶面积密度显然不同,相应的阻力系数也会存在差异。因此,采用植被冠层内部流场的理论模型探讨了阻力系数与风速以及叶面积密度两个因素的关系,得到了阻力系数的函数关系式。运用此关系式对气流进入云杉林前后的风速以及湍流强度进行了计算,并将所得模拟结果与野外观测的相关数据进行对比从而验证该关系式的准确性。3. 计算了叶面积指数、株间距、行间距、行数及分布方式和冠层宽度等因素对防护林阻风效果的影响。随着叶面积指数的增大,防护林的阻风效果增强。株间距越小,防护林的阻风效果越好。行间距越大,第二行树的背风面相同高度上相应位置的阻风效果越强。两行交错排列防护林的防风效果优于两行并列防护林,同时两行并列防护林比单行防护林的防风效果要好。冠层宽度对防护林的阻风效果影响比较明显。防护林冠层的最大宽度越大,阻风效果越好。

Other Abstract

Windbreaks play an important role in the conservation of water and soil, wind prevention and sand control and soil erosion. Therefore, it is very important to investigate the characteristics of wind field near the windbreaks for both theory and practice. At present, the major of the research of the characteristics of wind field near the windbreaks was field observation and experiments, but a part of the studies was numerical simulation, which mainly focus on the two-dimensional simulation. This paper discussed the relationship between the drag coefficient and its influence factors based on the previous research achievements, and the accuracy of the relationship was verified. At the same time, the influence of gaps between trees, gaps between rows, leaf area index, rows and settlements on the windbreak effect were studied. The primary coverage in this dissertation are as follows:1. The control equation of the wind field in the vegetation canopy was introduced and the derivation process was given in detail. On the basic of the time-average turbulent control equations, it was derived to utilize the space-average theory for the study of the wind field in the vegetation canopy. At the same time, the solving method and the value of the parameters of the model were discussed.2. The drag coefficient was regarded as a constant in the previous studies about the wind field in the vegetation canopy. However, the leaf area density along the height of the vegetation is different so that the wind resistance ability is obviously diverse, and the corresponding drag coefficient will change. Therefore, the theoretical model of the wind field in vegetation canopy was used to simulate the effects of wind speed and leaf area density on the drag coefficient, and the drag coefficient as a function of the leaf area density Cd=f(A) was obtained by means of curve-fitting. The wind speed and turbulence intensity of flow entering the spruce forest were calculated by using the function of drag coefficient, and the simulation outcome was compared with the field observation data to verify the accuracy of the function.3. The influence of gaps between trees, gaps between rows, leaf area index, rows and settlements, width of canopy on the windbreak effect were simulated. With the increase of leaf area index, the windbreak effect enhanced. The smaller the gaps between trees were, the better the windbreak effect was. The greater the gaps between rows, the stronger the windbreak effect of the corresponding position on the same height of the leeward of the second row. The windbreak effect of two-rows of staggering windbreak was the best, which compared with two-rows arranged in parallel windbreak and one-row windbreak. In addition, the windbreak effect of two-rows arranged in parallel windbreak was better than one-row windbreak. Width of canopy had a significant effect on wind resistance of windbreak. The greater the maximum width of canopy was, the better the effect of wind resistance was.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226547
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
万坤. 防护林风场特征的数值模拟[D]. 兰州. 兰州大学,2017.
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