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

为了研究这一课题，我们组织了以下三个小组：1.相干结构，2.二次流，3.在本项目的保护伞下，复杂河道中的纵向涡流。许多对该项目感兴趣的合作研究人员除了该项目的研究人员外，还加入了这三个小组。每年举行三到四次论坛，以相互了解结果，并通过论坛参与者的热烈讨论，集中讨论这一项目的目的研究中出现的问题。本课题的研究成果如下：1.相干结构：相干结构受初始条件和边界条件的影响，与减阻和过渡延迟直接相关。研究了不同类型流动中条纹状结构与纵向涡的关系。二次流：向跨度方向的动量传输在稳定二次流的产生中起着重要作用。这是由附加的纵向涡、不均匀的雷诺应力、离心力不稳定性和逆压梯度分离剪切层的不稳定性引起的。复杂流道中的纵向涡流：研究了波状流道中纵向涡流的贡献和控制、河流中的局部冲刷、湍流管流中稠密聚合物溶液的不均匀注入所引起的减阻以及床层中颗粒团的产生。该项目的研究成果在本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，并在许多会议或会议上以91篇演讲的形式发表了这一研究成果。

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.