RESEARCH ON THE GENERATION OF LONGITUDINAL VORTICES AND ITS CONTROL IN TURBULENT SHEAR FLOWS

为了研究这个项目，我们组织了以下三个小组，即：2.连贯结构；3.二次流；在这个项目的保护伞下的复杂通道纵向涡。除了该项目的研究人员外，许多对该项目感兴趣的合作研究人员也加入了这三个小组。论坛每年举行三到四次，通过论坛参与者的热烈讨论，相互了解结果，并将研究中出现的问题集中在这个项目的目标上。本课题的研究成果如下：相干结构：相干结构受初始条件和边界条件的影响，直接关系到减阻和过渡延迟。研究了不同类型流动中条纹结构与纵向涡的关系。二次流：动量向展向输运在稳定二次流的产生中起重要作用。它是由额外的纵向涡、不均匀的雷诺应力、离心不稳定和逆压梯度中分离剪切层的不稳定引起的。复杂通道中的纵向涡旋：研究了纵向涡旋对波浪通道中质量输运、河流局部侵蚀、湍流管道中密集聚合物溶液不均匀注入引起的减阻以及流化床中颗粒团簇的产生等方面的贡献和控制。同时研究了船体尾迹和落水时纵向涡的结构。该项目的研究成果在该项目的报告中发表了25篇论文，在各种期刊上发表了66篇论文，在许多会议或会议上发表了91次演讲。

To research this project, the next three groups were organized,i.e.1.Coherent structure, 2.Secondary flows and 3.Longitudinal vortices in complicated channels under the umbrella of this project. Many co-operative researchers who were intersted in this project joined the three groups besides the investigators of this project. Forums were held three or four times every year to get mutual understanding of the results and to focus problems occurring in the research on the aim of this project through lively discussions by the participants of the forum. The following are the research results of this project:1. Coherent structure: Coherent structure is affected by initial and boundary conditions and is related directly to the drag reduction and the delay of transition. The relation between streaky structure and longitudinal vortices was researched in various types of flow.2. Secondary flows: Momentum transport to the spanwise direction plays an important role in the generation of steady secondary flow. It is caused by additional longitudinal vortices, uneven Reynolds stress, centrifugal instability and instability of separation shear layer in adverse pressure gradient.3. Longitudinal vortices in complicated channels: Contribution and control of longitudinal vortices was researched on mass transport in a wavy channel, local erosion in a river, drag reduction caused by uneven injection of dense polymer solution in a turbulent pipe flow and generation of particle clusters in a fluidized bed. Structure of longitudinal vortices was also researched in the wake of a body and falling water.The research results of this project were published in 25 papers in the report of this project and in 66 papers in various journals and were presented in 91 presentations at many meetings or conferences.