沿海水杉及杨树林带三维结构参数模型和风流场数值模拟研究

发布时间：2018-06-11 14:50

本文选题：沿海防护林 + 水杉　；参考：《中国林业科学研究院》2017年硕士论文

【摘要】：为了更好地客观地阐明林带的空气动力学机理,提高林带边界层流数值模拟的精度。本研究以沿海水杉和杨树防护林带为研究对象,通过标准木解析,利用胸径、树高和冠层半径等指标,构建了水杉、杨树林带的三维结构参数模型;利用林带的三维结构参数模型计算了水杉、杨树林带的空气动力学参数,运用FLUENT软件进行林带风流场数值模拟,分析了不同林带的防护效应特征;并且对林带的密度调控和复层林构建两种结构调控措施进行了模拟,探讨了不同措施对林带防护效应的影响,筛选合适的林带结构,以期为沿海防护林带规划设计和经营管理提供依据。研究结果表明:(1)水杉林带的表面积密度变化范围为0.0012~3.4857 m2·m-3,体积密度变化范围为0.000002~0.012397 m3·m-3;杨树林带的表面积密度变化范围为0.0070~7.9337m2·m-3,体积密度变化范围为0.000008~0.008028m3·m-3。整体上,杨树林带的表面积密度和体积密度要大于水杉林带。林带结构在空间上有十分明显的异质性:树干的直径随着高度的上升而降低,水杉、杨树林带树干的表面积和体积也随之下降。水杉、杨树林带的枝下高分别为4m和6m,林带冠层以下形成了较大空隙。在林带冠层,枝条的表面积和体积密度随着高度先上升后下降。水杉枝条表面积和体积密度的峰值出现在冠层的中部,杨树则出现在冠层中上部。水杉叶片和枝条的分布特征较为一致,表面积和体积密度峰值出现的位置和枝条大致相同,杨树叶片则主要集中在冠层的上部。林带内各组分表面积和体积占总体的比例差异较大:水杉各组分表面积占总体比例为叶片(78.39%)枝条(16.04%)树干(5.57%),杨树为叶片(84.76%)枝条(12.13%)树干(3.11%);水杉各组分体积占总体比例为树干(75.28%)枝条(20.85%)叶片(3.87%),杨树为树干(67.81%)枝条(26.34%)叶片(5.85%)。水杉表面积体积比:叶片(20.23)枝条(0.77)树干(0.07),杨树表面积体积比:叶片(14.49)枝条(0.46)树干(0.05)。(2)通过对比水杉和杨树林带的风流场数值模拟结果发现,水杉和杨树林带前的气流变化趋势基本一致:气流在林带前4H-6H左右受到林带的影响,速度开始轻微下降,运动到达林带前2H位置,流速急剧下降。而林带后,气流变化趋势差异较大。在近地面区域,由于林带冠层有较大空隙,流速衰减幅度小于林带冠层区域。同时由于冠层枝叶密度较大,林带冠层气流发生分离、下沉,近地面气流受到挤压,流在林带后小范围有一定回升,随后受挤压的气流产生扩散,气流速度再次下降,之后缓慢恢复。冠层气流的衰减程度相对较大,但由于近地面气流的扩散,冠层气流与扩散的气流产生动量交换,气流速度在林后小范围内急剧上升,随后平缓恢复。对比水杉和杨树林带,由于杨树林带的整体密度要高于水杉林带,杨树林带各高度上的风速衰减和气流恢复速度基本都低于水杉林带,有效防护距离比水杉大12H以上。因此,本研究中杨树林带的防护效果要强于水杉林带。(3)不同株行距的水杉和杨树林带数值模拟结果表明:在林带前,气流流速受林带株行距的影响较小。在林带后,气流整体的变化趋势基本相同:气流的衰减幅度随着株行距的缩小而增加。各个高度上,株行距3m×2m和2m×2m的水杉林带与3m×3m的林带相比有效防护距离提升了2H-4H,杨树林带则提升了4H-7H。但林带株行距也不宜进一步缩小。对于水杉林带,株行距为2m×2m时,近地面速度接近于0,株行距进一步缩小林后将产生回流。株行距2m×2m的杨树林带与3m×2m的相比,气流回流范围有一定的扩大,回流位置有少许下移。综上,对于水杉林带,株行距2m×2m时,林带防护效应较好。但对于杨树林带,当防护目标高度较低时,株行距为2m×2m的防护效果较好,而当防护目标的高度较高时,林带的株行距最好设置为为3m×2m。(4)本研究中,通过林带下设置不同行数的灌木来模拟复层结构林带的构建,模拟结果显示:由于灌木的存在,林带冠层以下的空隙降低,近地面气流的衰减幅度明显提高,林带后气流度的加速效应明显降低;在林带冠层,林带冠层的气流下沉现象减少,因此气流速度的衰减幅度下降。但林后动量交换程度明显减弱,林后0-5H的气流恢复速度明显减缓。在林带较远位置,各高度上的气流速度差异逐渐变小,有效防护距离差异不大。在冠层的中上部,种植两行灌木的林带的有效防护距离反而下降。综上,林下种植灌木可以有效地改善林带近地面防护效应,但对于冠层中上部的气流影响不明显,甚至可能产生负面影响。
[Abstract]:In order to better and objectively clarify the aerodynamic mechanism of the forest belt and improve the precision of the numerical simulation of the boundary laminar flow in the forest belt. This study takes the coastal metasequoia and poplar shelterbelt as the research object. Through the standard wood analysis, the three-dimensional structural parameters model of the metasequoia and poplar belt is constructed by using the diameter of the breast, the height of the tree and the radius of the canopy. The aerodynamic parameters of the metasequoia and poplar belt were calculated with the three-dimensional structural parameter model. The FLUENT software was used to simulate the wind flow field of the forest belt, and the protective effects of different forest belts were analyzed. The density control of the forest belts and the construction of two kinds of structure control measures were simulated, and the different measures for forest belt prevention were discussed. In order to provide the basis for the planning and management of coastal shelterbelts, the results show that: (1) the range of surface area density of the Metasequoia forest belt is 0.0012~3.4857 M2 M-3, the range of volume density is 0.000002~ 0.012397 m3. M-3; the range of surface area density of the poplar belt is changed. The density and volume density of the poplar area is greater than that of the Metasequoia forest. The density and volume density of the poplar belt are larger than that of the Metasequoia forest zone. The structure of the forest belt is very heterogeneous in space: the diameter of the tree stem decreases with the height of the tree, and the surface area and volume of the tree trunk with the 0.0070~7.9337m2 and the poplar trees. The lower branch height of the metasequoia and poplar belt is 4m and 6m respectively. A larger gap is formed below the canopy of the forest belt. In the canopy of the forest, the surface area and volume density of the branches decrease with the height first. The peak of the surface area and volume density of the Metasequoia branches appears in the middle of the canopy, and the poplar tree appears in the upper part of the canopy. The distribution of slices and branches is the same. The position of the peak value of the surface area and volume density is roughly the same. The poplar leaves are mainly concentrated in the upper part of the canopy. The total proportion of each sub surface area and volume in the forest belt is larger: the total proportion of the Metasequoia Metasequoia is 78.39% branches (16.04%) tree trunk (5.). 57%) poplar trees (84.76%) branches (12.13%) tree trunk (3.11%); the total proportion of each component of the Metasequoia (75.28%) branches (20.85%) leaves (3.87%), poplar tree trunk (67.81%) branches (26.34%) leaves (5.85%). The surface area volume ratio of the Metasequoia (20.23) branches (0.77) tree trunk (0.07), poplar tree area volume ratio: leaf (14.49) branches) 6) tree trunk (0.05). (2) by comparing the numerical simulation results of the wind flow field in the metasequoia and poplar belt, it was found that the trend of the air flow in the front of the metasequoia and poplar forest was basically the same: the air flow was affected by the forest belt around 4H-6H before the forest belt, the velocity began to decrease slightly, the movement to the front of the Darin belt was 2H, and the flow velocity dropped sharply. In the near ground area, the flow velocity attenuation amplitude is less than that of the canopy area. At the same time, the flow velocity attenuation amplitude is less than that of the canopy area. At the same time, due to the large density of the canopy and leaf, the flow of the canopy in the forest belt is separated, sinking, the near ground air flow is squeezed, and the flow in the small range has a certain recovery after the forest belt, and then the compressed air produces diffusion and airflow. The velocity decreases again and then slowly recovers. The attenuation of the canopy flow is relatively large, but due to the diffusion of the near ground air flow, the air flow has a momentum exchange with the diffused airflow, and the velocity of the air flow rises sharply in the small range after the forest, and then slowly recovers. The overall density of the poplar belt is higher than the water. The attenuation of wind speed and the speed of air flow recovery at the height of the poplar belt are basically lower than that of the Metasequoia, and the effective protection distance is more than 12H of the metasequoia. Therefore, the protective effect of the poplar forest belt in this study is stronger than that of the Metasequoia forest zone. (3) the numerical simulation results of the metasequoia and poplar belt with different row spacing show that the flow velocity before the forest belt The influence of the line spacing was small. After the forest belt, the trend of the air flow was basically the same: the attenuation of air flow increased with the decrease of line spacing. At each height, the effective protection distance of 3M * 2M and 2m x 2m in each height was 2H-4H compared to the 3M * 3M forest belt, while the poplar belt raised the 4H-7H. but the forest belt line. When the distance of plant line is 2m x 2m, the near ground speed is close to 0, and the line distance of the plant line is more than that of 2m x 2m. Compared with 3M * 2m, the flow range of the air flow is enlarged and the reflux position is little moved down. To sum up, when the line distance of the Metasequoia forest is 2m x 2m The protective effect of the forest belt is better. But for the poplar belt, when the height of the protective target is low, the line spacing of 2m x 2m is better. When the height of the protective target is high, the line spacing of the forest belt is best set for the 3m x 2M. (4) study, and the construction of the complex structure forest belt is simulated by setting the shrubs with no number of peers under the forest belt. The simulated results show that the gap in the canopy below the canopy of the forest is reduced because of the existence of shrubs, the attenuation amplitude of the air flow near the ground is obviously increased, and the acceleration effect of the air flow is obviously reduced after the forest belt. The airflow recovery speed of 0-5H after forest was obviously slowed down. In the far position of the forest belt, the difference of air velocity in each height was gradually smaller and the difference of effective protection distance was not significant. In the middle and upper part of the canopy, the effective protection distance of planting two rows of shrubs was decreased. In conclusion, the planting shrubs under forest could effectively improve the protective effect of the forest belt near the ground. But there is no obvious or even negative effect on the airflow in the upper and middle parts of the canopy.
【学位授予单位】：中国林业科学研究院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S718.5

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