Statistics of stretching of fluid lines and surfaces, and turbulent mixing

流体线和表面的拉伸以及湍流混合的统计

基本信息

批准号：
14540385
负责人：
KIDA Shigeo
金额：
$ 2.62万
依托单位：
Kyoto University (2003-2004)National Institute for Fusion Science (2002)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14540385/
关键词：
Turbulent mixing Fluid line Fluid surface Stretching rate Tubular vortex Anti-parallel vortices 流対面伸張率

项目摘要

For the purpose of understanding of dynamics and qualitative description of statistics of turbulent mixing the stretching characteristics of fluid lines and surfaces are investigated numerically. The results obtained are summarized as follows. First, we examined, by use of direct numerical simulation and visualization analysis, how they are deformed and at which ratio they are being stretched in homogeneous stationary turbulence. It is shown theoretically that both the length of fluid line and the area of fluid surface increase exponentially in time, and that the accurate values of the stretching rate can never be obtained by the traditional method, i.e. with passive line or surface elements, but only by solving accurately the motion of the fluid lines and surfaces as the present study. Second, it was identified with simultaneous visualization of passive lines and fluid flows the type of fluid motion which causes strong stretching of fluid lines. There exist a number of tubular vortice … More s with concentrated vorticity in turbulence. They have a tendency to approach each other in parallel with opposite direction of vorticity. Fluid lines are stretched strongly around stagnation points of hyperbolic type associated with a pair of anti-parallel vortices. Third, a careful examination of the Reynolds number dependence of stretching rate of fluid line exhibits that it does not obey the Kolmogorov similarity law (as believed before) but increases more rapidly with the Reynolds number. This may be due to the Markovian multiplicative characteristics of the stretching process, i.e. the non-uniformity of the spatial distributions of stretched fluid line, especially the degree of fold, increases with the Reynolds number. The precise value of the exponential stretching rates of passive objects in turbulence and its Reynolds dependence would be useful in determination of parameters in turbulence modeling as well as important in understanding of dynamical characteristics of turbulence itself. Less

为了理解动力学和定性描述湍流混合的统计数据，基本上研究了流体线和表面的拉伸特征。获得的结果总结如下。首先，我们通过使用直接的数值模拟和可视化分析来检查它们的变形以及它们在均质固定湍流中的较高比率。据理论上表明，流体线的长度和流体表面的面积都在指数及时增加，并且无法通过传统方法（即使用被动线或表面元素）获得伸展速率的准确值，而仅通过准确求解流体线和表面的运动作为本研究。其次，通过简单可视化被动线的可视化和流体流动的流体运动类型，从而导致流体线的强烈拉伸。存在许多管状涡流…更多的s含有浓缩的湍流。他们倾向于与涡度相反的方向并行接近。流体线在与一对反行涡流相关的双曲线类型的停滞点上强烈拉伸。第三，仔细检查了流体线拉伸速率的雷诺数依赖性，表明它不遵守Kolmogorov的相似性法（以前认为），但随着雷诺数的数量而增加。这可能是由于拉伸过程的马尔可夫乘法特征，即拉伸流体线的空间分布的不均匀性，尤其是折叠程度，随着雷诺数的增加而增加。被动物体在湍流及其雷诺依赖性中被动物体的指数拉伸速率的精确值将有助于确定湍流建模中的参数，并且对于理解湍流本身的动态特征的重要性。较少的