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Development of computational method for gravity currents in the ocean

海洋重力流计算方法的发展

基本信息

批准号：
10555347
负责人：
BABA Nobuhiro
金额：
$ 2.43万
依托单位：
Osaka Prefecture University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10555347/
关键词：
Gravity Current Head Mixing Lock-Exchange Flow Flow Visualization Navier-Stokes Equation 画像解析可視化実験

项目摘要

The structure of the head of gravity currents is investigated in the experiment and the computation of lock-exchange flow. A finite volume of fluid was released instantaneously in another fluid of slightly different density in an open rectangular channel when a lock gate was opened. A box model was introduced to describe different regimes of a developing gravity current on the basis of energy argument.Visualization experiments were made by the shadowgraph method and with dye to trace the head of gravity currents, the results of which validate the box model. The initial depth and volume of the released fluid affect the front speed. At the first stage the released fluid spreads at a constant speed, and then it slows down so that the front speed decreases with time to the power of -1/3 in self-similar regime. The current that has begun to be dominated by viscosity slows down further in the final stage during which the front speed decreases with time to the power of -4/5.The computation wa … More s also made in the same condition as the experiments to study the structure of the head of currents in different regimes. The incompressible Navier-Stokes equation for an inhomogeneous fluid together with the transport equation for solute was solved by the finite volume method developed in the previous paper. The computation produces the transition between the development regimes so that the front speed obtained from the computed density field is in good agreement with the experimental result. The computational results indicate that the transition to the next regime is accompanied by remarkable change in the geometry and the inner structure of the head. The head has maintained a sharp density interface even at low Reynolds number and the relatively large-scale entrainment of ambient fluid across the upper interface causes strong mixing behind the head. The models with the inviscid boundaries failed to catch the transition to the second stage, which suggests that the transition may require some stimulus associated with viscous motions. The result for the case of short lock-length shows the sudden decrease in the volume and in the density of the head brought about by the vortex shedding along the upper interface, which may be one of the mechanism to account for the strong mixing in the first and the second regimes. Less

实验研究了重力流头的结构，并对锁交换流量进行了计算。当闸门打开时，在一个开放的矩形通道中，有限体积的流体瞬间被释放到另一种密度略有不同的流体中。在能量论证的基础上，引入了一个箱形模型来描述发展中的重力流的不同状态。采用阴影法和染色法对重力流头部进行了可视化实验，验证了箱形模型的正确性。释放流体的初始深度和体积影响前转速。在第一阶段，释放的流体以恒定速度扩散，然后减速，使前速度随时间减小至自相似状态的-1/3次方。在最后阶段，已经开始以粘度为主导的电流进一步减慢，在此期间，前速度随时间降低至-4/5的幂。并在与实验相同的条件下进行了计算，研究了不同工况下的流头结构。用有限体积法求解了非均匀流体的不可压缩Navier-Stokes方程和溶质的输运方程。计算产生了发展状态之间的过渡，使密度场计算得到的前速度与实验结果吻合较好。计算结果表明，在过渡到下一个状态时，头部的几何形状和内部结构都发生了显著的变化。即使在低雷诺数下，头部也保持了一个尖锐的密度界面，并且相对大规模的环境流体穿过上部界面导致头部后的强烈混合。无粘边界模型未能捕捉到过渡到第二阶段，这表明过渡可能需要一些与粘性运动相关的刺激。在短锁长的情况下，沿上部界面的涡脱落导致了封头体积和密度的突然减小，这可能是导致第一和第二流强混合的机制之一。少