【作者】 赵芳；

【导师】 槐文信；

【作者基本信息】 武汉大学 ， 水力学及河流动力学， 2017， 博士

【摘要】 本文通过水槽实验和数值模拟研究了四种刚性植被形式作用下明渠的水动力特性,四种植被形式为双层植被、不连续植被斑、漂浮植被和树冠状植被。基于PIV进行了双层植被水流试验,考虑不同流量、水深及植被排列方式,得到了纵向流速垂向分布概化图,流速在低植被层和高植被层内流速基本均匀分布,在渠底有突增现象,在高植被层和低植被层顶部存在拐点,自由水层符合对数律分布,高层植被非淹没情况下涡量最大值出现在低植被层顶部偏下位置且交错布置工况的涡量最大值为线性布置工况的5-6倍,交错排布植被更有利于固定河滩;高层植被淹没时,排布方式对流速、涡量和雷诺应力的影响不大,涡量和雷诺应力在高、低植被层顶部较大,高层植被顶部处的涡量和雷诺应力明显大于低植被层顶部,通过流速判断线性排布植被更有利于防洪固滩。通过水槽实验和大涡模拟研究不连续植被斑水流,考虑不同的植被密度、雷诺数和植被斑之间间隙区长度,不连续植被斑水流纵向流速与雷诺应力分布变化受植被密度和雷诺数的影响较大,改变植被斑和间隙区的长度对纵向流速与雷诺应力的影响不大,但是较长的植被斑与间隙区长度更有利于水流的沿程调整;间隙区的纵向流速小于植被斑区域的流速,更有利于来流中悬浮物的沉积;通过象限和频谱分析,下扫主要在植被层垂向交换区占主导,喷射主要在自由水层占主导,主要有两种尺度的涡旋作用于植被斑区域,茎干尺度涡和剪切尺度涡。基于Delft3D中三维刚性植被模型模拟了漂浮植被水流,用两组试验数据进行验证吻合较好;根据水流在漂浮植被和渠底阻力影响下的调整过程,将水流沿程分为扩散流动区、发展进行区和充分发展区;在发展进行区起始位置植被层下方间隙区出现纵向流速局部突增区,分析了局部突增区长度尺度和植被前缘到水流充分发展所需的长度尺度随植被密度和间隙区高度的变化;并初步给出了渠底边界层厚度与间隙区高度(hg)及无量纲植被阻力参数(Caahc)的关系式。针对树冠状植被水流,采用ADV测量了不同流量和水深工况下的三维流速,将树冠状植被水流沿垂向分为树干层、树冠层和无植被层;纵向流速在树干层近似均匀分布,在树冠层先减小后增大,在无植被层符合对数分布;紊动强度和雷诺应力在树冠层较大,在树干层和无植被层较小;通过象限分析,发现下扫作用主要在植被层占主导,喷射作用主要在自由水层占主导。更多还原

【Abstract】 In this dissertation,the hydrodynamics in open channel with four forms of rigid vegetation patches are discussed in detail with flume experiments and numerical simulation.Four vegetation forms are double-layer vegetation,discontinuous vegetation patches,suspended canopy and tree-like canopy.The flume experiments of double-layer vegetation flow were based on the Particle Image Velocimetry(PIV)system.Different flow rate,water depth and dowel arrangement are considered.A schematic profile of longitudinal velocity for double-layer vegetation flow is presented.The longitudinal velocity profile is nearly constant in the lower zone of each vegetation layer and increases in the upper zone with inflection points at the top of short vegetation layer and tall vegetation layer.The individual measuring points near the bed form the velocity spike.In the layer without vegetation,the longitudinal velocity follows the log-law.For the submerged single layer cases,the maximum of vorticity occurs at the top of short vegetation layer.The vorticity peak of staggered configuration is 5 to 6 times bigger than that of linear configuration.The staggered configuration is conducive to reducing bank erosion.For the submerged double layer cases,the vorticity and Reynolds stress,not influenced by dowel arrangement,at the top of tall vegetation layer are bigger than that at the top of short vegetation layer.The linear configuration is helpful for flood control and river bed protection.For discontinuous vegetation patches flow,different patch density,Reynolds number and gap length cases are conducted in the experiments and Large Eddy Simulation method.The evolutions of longitudinal velocity and Reynolds stress are related to patch density are Reynolds number.The hydrodynamics in open channel are more stable for long gap length case,which is also benefit to the flow adjustment.The longitudinal velocity in gap zone is much smaller than that in patches zone and backflow occurs in gap zone.According to the quadrant and spectrum analysis,the sweep is dominated in vertical exchange zone at the upper part of patches and ejection is dominated in free water layer.Two vortex scales,stem-scale and shear-scale,play a key role in the patches zone.The suspended canopy flow is simulated by the Rigid 3D Vegetation model based on Delft3D software.Two experimental data sets are used to verify the numerical model.And the results of numerical model are in good agreement with the data sets.The flow adjustment is divided into three zones(diverging flow zone,developing zone and fully developed zone)in the streamwise direction.The velocity local extreme zone in the gap beneath the canopy is found around the leading edge of the developing zone.The length scale of velocity local extreme zone and fully developed zone is significantly influenced by canopy density and gap thickness.The bed boundary layer thickness is linked to gap thickness(hg)and non-dimensional flow blockage parameter(Cdahc).The experiments of tree-like canopy,based on ADV,are conducted in the Laboratory of Applied Hydraulics,NTUA.The submerged tree-like canopy flow in the vertical direction consists of stem layer,tree layer and no-canopy layer.The longitudinal velocity is almost constant in the stem layer.Then it decreases firstly then increases with increment of depth in the tree layer.Strong fluctuation of turbulence intensity and Reynolds stress is found in the tree layer.The longitudinal velocity in no-canopy layer follows logarithmic law.The quadrant analysis recovers the tree layer is the sweep-dominated area and no-canopy layer is the ejection-dominated area.更多还原