Extreme phenomena of turbulence under strongly stable stratification conditions

强稳定分层条件下湍流的极端现象

基本信息

批准号：
09490029
负责人：
UEDA Hiromasa
金额：
$ 6.85万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09490029/
关键词：
Stratified flow Turbulence Stable stratification Internal gravity wave Counter gradient diffusion Turbulent diffusion Turbulence model Linear theory 密度成層乱流構造乱流渦気液界面レーザー蛍光法逆勾配散 PIV

项目摘要

In turbulent flows under extremely strong stably straified conditions flow pattern and diffusion and mixing mechanisms are drastically changed, and transition of turbulent eddy motion into wavy motion plays a substantial role and causes such drastic changes. From this point of view, this research project was aimed to investigate experimentally the characteristics of turbulence and intemal wave and the evolution of internal wavy motion in the stratified turbulent flow and to derive a unified explanation on the extreme phenomena which appear under strong stratification conditions. Extreme phenomena includes counter-gradient diffusion in the vertical direction, and horizontal diffusion and difference between active and passive scalar diffusion mechanisms in the counter-gradient diffusion field.It was found that the counter gradient diffusion and the associated phenomena under strongly stable stratification for zero shear cases was explained quite well by a liner theory. In addition, the theory was extended for the cases when both the shear and stratification exist, and explained such extreme phenomena successfully. It indicates that quite a large part of the extreme phenomena can be considered to be linear processes, although their time evolution is influenced by the initial conditions.Basing upon the new concept mentioned above, a turbulence closure model for the stratified flows was developed in which fluid motion was divided into mean, wave and turbulence components and nonlinear interactions between them were modeled, and the model parameters were determined by the experimental results.

在极强的稳定分层条件下的湍流中，流动模式以及扩散和混合机制发生了巨大的变化，而湍流涡流运动向波状运动的转变起着重要作用并导致了这种剧烈的变化。从这个角度来看，本研究项目旨在通过实验研究分层湍流中湍流和内波的特征以及内波运动的演化，并对强分层条件下出现的极端现象得出统一的解释。极端现象包括垂直方向的反梯度扩散、水平扩散以及反梯度扩散场中主动标量扩散机制与被动标量扩散机制的差异。发现零强稳定分层下的反梯度扩散及其相关现象线性理论很好地解释了剪切情况。此外，该理论还推广到了剪切和分层同时存在的情况，成功地解释了这种极端现象。这表明相当大一部分极端现象可以被认为是线性过程，尽管它们的时间演化受到初始条件的影响。基于上述新概念，建立了分层流的湍流闭合模型，其中将流体运动分为平均分量、波动分量和湍流分量，对它们之间的非线性相互作用进行建模，并根据实验结果确定模型参数。