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Investigation of the flow characteristics with one-line emergent canopy patches in open channel
Journal of Hydrology ( IF 6.4 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.jhydrol.2020.125248
Dian Li , Wen-xin Huai , Meng-yang Liu

Abstract Experiments are performed on channels with emergent one-line porous canopy patches distributed along the channel sidewalls in which flow dynamics and turbulent structures are analyzed. The evolution of the transverse distribution of the mean streamwise velocity and Reynolds stress profiles in specific transverse sections with downstream distance suggests that a fully equilibrated zone is reached beyond an adjustment distance, and the adjustment distance needed for vegetation with high solid volume fractions is short. The flow field can be divided into three main different regions based on the transverse distribution of the mean streamwise velocity and Reynolds stress in the equilibrium zone: a boundary-affected region, an analog mixing layer, and a uniform region in a non-vegetated area. The analog mixing layer exhibits a two-layer structure governed by local coherent vortices. The dominant frequencies of the vortices at the interface are determined through spectral analysis and proven to correspond to a patch scale. The development of the shear layer, the analysis of the frequencies and scales of the vortices, and the experiment on flow visualization indicate that von-Karman vortices continue to form downstream despite the interference of the sidewall and the special one-line distribution pattern of patches. Quadrant analysis is adopted to illustrate the lateral momentum exchange caused by different motions. Results show that ejections and sweeps are the main contributions to Reynolds stress in the analog mixing layer. Different signs of Reynolds stress in the boundary-affected region and the analog mixing layer can also be explained through quadrant analysis.

中文翻译:

明渠单线突水冠层水流特性研究

摘要 对具有沿通道侧壁分布的单线多孔冠层斑块的通道进行了实验,分析了流动动力学和湍流结构。平均流向速度和雷诺应力分布在特定横断面随下游距离的横向分布的演变表明,在调整距离之外达到完全平衡区,并且具有高固体体积分数的植被所需的调整距离很短。根据平衡区平均流向速度和雷诺应力的横向分布,流场可分为三个主要不同区域:边界影响区、模拟混合层和无植被区的均匀区. 模拟混合层呈现出由局部相干涡流控制的两层结构。界面处涡旋的主要频率是通过光谱分析确定的,并被证明与斑块尺度相对应。剪切层的发展、涡旋频率和尺度的分析以及流动可视化实验表明,尽管受到侧壁的干扰和斑块的特殊单线分布模式,von-Karman涡旋仍在下游继续形成. 采用象限分析来说明不同运动引起的横向动量交换。结果表明,喷射和扫描是模拟混合层中雷诺应力的主要贡献。
更新日期:2020-11-01
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