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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.

本文描述河口高度分层流的非定常混合机制。风、潮汐、流量和外部诱导湍流在1997年和1998年对受潮汐影响的石狩川下游45公里进行的研究中，收集了以下数据：1）在6个地点连续两个月自动记录表层盐度; 2）在2个地点连续两周垂直记录6个深度的盐度;（3）用声波测深仪在三个地点进行了两个月的界面深度测量，结果表明：（1）在半日潮期间，盐楔界面位置的变化幅度是潮差的n倍;从河口到上游约7 km处，N逐渐增加，然后逆转增加的趋势，在上游26 km处减小到约为零。最初认为，由于河流拓扑结构，界面波动在上游7 km处达到最大值，但原因尚不清楚。2)通过垂直盐度分布的观测，解释了表面盐度与风的关系。盐在界面上的扩散增加了风，而上层的盐浓度梯度仍然很低。这意味着，由于风引起的过程而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和4 m深度之间观察到2.5 s和10 - 20 s周期的河流流速波动。这两种波动都是由波的作用引起的，但是在观测到这些波动的任何时候都没有界面，所以它们不可能是由界面波引起的。