Entrainment Phenomena in a Stratified Flow with Average Velocities and Turbulent Surface Layers

具有平均速度和湍流表面层的分层流中的夹带现象

基本信息

批准号：
09450186
负责人：
YOSHIDA Shizuo
金额：
$ 2.62万
依托单位：
Hokkaido 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-09450186/
关键词：
River mouth flow Two layer flow Salt wedge Entrainment coefficient Interfacial instability Richardson number Tide Wind wave

项目摘要

This report describes unsteady mixing mechanisms in highly stratified flow at river mouths. Wind, tide, flowrate and externally induced turbulence (from waves) are the factors considered here.The following data were taken in studies of the lower 45 km of the Ishikari River, whose level is affected by the tide, in 1997 and 1998: 1) Automatic recordings of surface salinity for two months at six locations; 2) salinity at six depths in a vertical line for two weeks at two locations; 3) depth of the interface, using a sonic depth finder, at three locations for two months.The results of the studies are summarized as follows: 1) During semidiurnal tides, the amplitude of the variation in position of the salt wedge interface is n times the tidal difference; n increases gradually from the mouth to about 7 km upstream, then reverses the increasing trend, diminishing to about zero at 26 km upstream. It was originally thought that the interface fluctuation reaches a maximum at 7 km upstream due to river topology, but the reason remains unknown. 2) The relation of surface salinity with wind has been explained by the observations of vertical salinity distribution. Diffusion of salt across the interface is augmented by increased wind, while the salt concentration gradient in the upper layer remains very low. This means that the salt entrained into the upper layer due to wind-induced processes is immediately distributed through the layer; ordinary diffusion processes can not be responsible for this. 3) Fluctuations in river flow speed with periods of 2.5 s and 10 - 20 s were observed between 0 and 4 m depth. Both fluctuations arise from wave action, but there was no interface at any of the times these fluctuations were observed, so they can not be caused by interface waves.

该报告描述了河口高度分层流的不稳定混合机制。风，潮汐，流量和外部诱导的湍流（来自波浪）是此处考虑的因素。 2）在两个位置在垂直线的六个深度处的盐度； 3）界面的深度，使用声音深度查找器在三个位置进行了两个月。研究结果总结如下：1）在半潮汐潮汐期间，盐楔界面位置变化的幅度是潮汐差的N倍； n逐渐从嘴巴上游逐渐增加，然后逆转趋势的增加，在上游26 km时减少到零。最初认为，由于河流拓扑而导致的界面波动在上游7公里处达到最大值，但原因仍然未知。 2）表面盐度与风的关系已经通过垂直盐度分布的观察结果来解释。盐在界面中的扩散会因风增加而增加，而上层的盐浓度梯度保持非常低。这意味着由于风引起的过程而导致上层夹带的盐立即通过层分布。普通的扩散过程不可能为此负责。 3）在0到4 m的深度之间观察到河流流速为2.5 s和10-20 s的波动。两种波动都是由波动作用引起的，但是在任何时候都没有界面观察到这些波动，因此不能由界面波引起。