Turbulent Structure of Canopy Flows using Large-Eddy Simulation: Homogeneous and Inhomogeneous Surfaces

湍流是地球表面和低层大气之间的热量、水蒸气、二氧化碳和其他量的传输。植物和森林冠层对流经它们的风有很强的影响，因此改变了交换过程。该项目是对独特流动模式（连贯结构）工作的延续，这种流动模式对发生在树冠和表层之间的交换做出了重大贡献。冠层与上覆层空气界面处的强速度梯度导致湍流的组织程度相对较高，表现为强速度相关性、高速度偏度、间歇性以及一致和重复的流型。使用大涡模拟（LES）的计算方法，工作的主要目标是：-开发可视化和检查在计算冠层流场中发现的相干模式的方法。-通过构建组成结构的各种元素的框架来创建连贯结构的描述。-检查流动结构的涡状性质。-进行模拟，以检查非均匀条件的影响，例如在森林边缘。-检查这些过渡区的流场的统计特性，以及施加在个别树木上的力，以评估风损害的可能性。通过分析植物冠层元素（叶、枝、干）与风相互作用的物理特性，为解释冠层内的运输过程提供了基础。

Turbulence accounts for the transport of heat, water vapor, CO2 and other quantities between the surface of the earth and the lower atmosphere. Plant and forest canopies have a strong effect on the wind flowing through them and hence modify the exchange processes. This project is a continuation of work on the distinctive flow patterns (coherent structures) that make a substantial contribution to the exchanges that take place between canopies and the surface layer. The strong velocity gradient at the interface between the canopy and the overlying layer of air induces a relatively high degree of organization to the turbulence, evidenced by strong velocity correlations, high velocity skewness, intermittency, and consistent and repeated flow patterns. Using the computational method of large-eddy simulation (LES), the main objectives of the work are:- Develop methods to visualize and examine the coherent patterns found in computed canopy flow fields.- Create descriptions of coherent structures by constructing a framework of the various elements of which the structures are composed.-Examine the vortex-like nature of the flow structures.- Perform simulations to examine the effects of inhomogeneous conditions, for example at forest edges.- Examine the statistical properties of the flow fields in such transition zones, and also the forces exerted on individual trees, to asses the potential for wind damage.By analyzing the physics of interactions between elements of the plant canopy (foliage, branches, and tree trunks) with the wind, the work provides a basis for explaining transport processes in the canopy.