Experimental and Analytical Study on Water Quality Transfer Induced by Wind Shear Stress in Stratified Water Areas

实验和分析工作进行检查流和水质传输引起的风切应力作用在分层水域的表面。这种情况在许多封闭水域如湖泊、水库、内陆海湾等都存在，在这些水域中，密度分层对流体运动起着重要作用，风切应力是水体输运的主要驱动力。从水圈环境的角度来看，迫切需要建立一个基于水动力学理论背景的环境评价工具。为满足工程需要，本研究项目围绕以下三个方面展开：（1）风场特性及风驱动环流形成机理的野外和数值研究;（2）风应力作用下剪切层湍流结构的试验和大涡模拟;（3）海湾流场的三维数值模拟。主要结果如下。(1)A文件M 关于我们 在一座四面环山的大坝顶部进行了风速和风向的测量，以研究其作为水库流体运动驱动力的特性。结果表明，风向受库区地形影响较大，与库区附近平坦地区气象站观测的风向基本无关，而风速与该地区气象站观测的风速有较好的相关性。因此，建议在利用风场数据理论再现水域中的风驱动流体运动之前，需要仔细检查风场。一个k-ε湍流模型进行检查的垂直环流和混合驱动的风切变。通过分析，得到了底层水上升流量、跃层卷吸率和边界混合强度与密度结构和表面切应力的关系，为建立水质预测工具奠定了基础。(2)温跃层界面上的风切变层是分层水体中垂直水质交换的主要机制。为了建立一个能够描述剪切主导流（如风驱动流）中湍流的理论模型，需要找到其动力学。利用超声摄像技术和PIV图像处理方法对剪切层速度进行了测量。在那里发现了一些有组织的湍流结构的层次，这是非常相似的壁湍流中观察到的。大涡模拟对流动结构的再现效果较好，模拟结果与实验结果基本一致。研究了风场中剪切层湍流对水质迁移的促进作用。(3)对大坂湾和东京湾的水动力进行了实验和数值研究。特别是在东京湾，由于缺氧底层水的涌升而引起许多水质问题，这给沿着的渔场带来了严重的损害。通过室内实验研究了底层水涌升的机理。上升流速率与风速和密度结构的函数关系。一个三维模型也参数化，以重现在两个海湾的风驱动电流。模型性能相当令人满意，模拟的流场与现场数据吻合良好。预计该模型可实际用于评估海湾和沿海地区一些建设工程后的环境变化，最后报告已于1996年5月出版并送交日本水利工程研究所。少

Experimental and analytical works are carried out to examine flow and water quality transport induced by wind shear stress acting on the surface of stratified water areas. Such a situation is found in many enclosed water areas such as lakes, reservoirs, land-locked bays, where density stratification plays an important roles in fluid motions and the wind shear stress is a major driving force of water mass transport. From a view point of hydrosphere environment it is urged to construct an environmental assessment tool based on a theoretical background of hydrodynamics. In order to meet engineering demands, this research project is organized so as to cover the following three themes ; (1) field and numerical works on wind field properties and formation mechanism of wind-driven circulation, (2) experimental and LES simulation on turbulent structure of shear layr generated by wind stress, (3) three dimensional modeling of flow field in bay areas. The major results are followed.(1) A filed m … More easurement on wind velocity and direction is carried out at the top of a dam surrounded by mountains to investigate its properties as a driving force of reservoir fluid motions. It is found the wind direction is profoundly affected by the local terrain around the reservoir and is almost independent on the wind direction observed at a meteorological station located in a nearby flat area, while the wind speed there has a good correlation with data from the station. From this, it is suggested one need to carefully examine wind fields before theoretically reproducing wind-driven fluid motions in water areas by using wind data. A k-epsilon turbulence modeling is performed to examine the vertical circulation and mixing driven by the wind shear. Through the analysis, it is found how amount of bottom water upwelling, entrainment rate across the thermocline and the boundary mixing intensity depend on the density structure as well on the surface shear stress, which would be a first step of construction of water quality prediction tools.(2) It is known that the wind-driven shear layr developing at the thermocline interface is a major mechanism being responsible for vertical water quality exchange in a stratified water body. For formulating a theoretical model being able to describe turbulence in a shear-dominant flow like wind-driven flows, it is required to find its dynamics. A velocity measurement of shear layr is carried out by using a ultrasonic video camera and PIV image processing method. Some hierarchy of organized turbulent structures are found there, which are quite similar to those observed in wall turbulence. LES performance in reproducing flow structure is quite well ; the result are in almost complete agreement with the experiment. It is investigated how the shear-layr turbulence promotes water quality transfer in wind-driven flow fields.(3) Experimental and numerical investigation are carried out to get hydrodynamics in Osaka and Tokyo Bays. Especially in Tokyo Bay, many water quality troubles arise due to upwelling of anoxic bottom water, which brings serious damages to fishery farms along the coast. A laboratory experiment is carried out to examine mechanism of bottom water upwelling. A functional relationship of the upwelling rate on wind velocity and density structure. A three dimensional model is also parameterized in order to reproduce wind-driven currents in the two bays. Model performance is quite satisfactory ; the simulated flow fields are in good agreement with the field data. It is expected that the model could be of practical use in assessing environmental changes after some construction works in bays and coastal areas.The final report is published and delivered to Japanese institutions of hydraulic engineering in May 1996. Less