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.

本报告描述了河口高度分层流中的不稳定混合机制。这里考虑的因素有风、潮汐、流量和外部引起的湍流（来自波浪）。以下数据是在 1997 年和 1998 年对石狩河下游 45 公里处的研究中获取的，该河段的水位受潮汐影响：1 ) 在六个地点自动记录两个月的表面盐度； 2) 两个地点的两周内垂直线上六个深度的盐度； 3) 使用声波测深仪在三个地点进行两个月的界面深度研究。研究结果总结如下： 1) 在半日潮期间，盐楔界面位置变化的幅度为 n倍潮差； n从河口到上游约7公里处逐渐增加，然后反转增加趋势，在上游26公里处减小至约0。最初认为由于河流拓扑的原因，界面波动在上游7公里处达到最大，但原因尚不清楚。 2)通过盐度垂直分布的观测解释了地表盐度与风的关系。风的增加增强了盐在界面上的扩散，而上层的盐浓度梯度仍然很低。这意味着由于风引起的过程夹带到上层的盐立即分布在整个层中；普通的扩散过程不能对此负责。 3)在0~4 m深度之间观察到河流流速的波动周期为2.5 s和10~20 s。这两种涨落都是由波作用引起的，但在观察到这些涨落的任何时候都不存在界面，因此它们不可能是由界面波引起的。