Three-Dimensional Instability of the Head of Gravity Currents
Three-Dimensional Instability of the Head of Gravity Currents
复制标题
重力流头部的三维不稳定性
DOI：
10.2534/jjasnaoe1968.1999.119
复制
发表时间：
1999
期刊：
影响因子：
--
通讯作者：
Satomi Ito
中科院分区：
文献类型：
--
作者：
N. Baba;Y. Sakaguchi;Satomi Ito
在实验和锁交换流计算中研究了重力流头的三维不稳定性。用染料进行可视化实验，观察头部沿矩形截面明渠推进的三维特征。将前人提出的重力流计算方法推广到三维情况，并应用于锁交换流问题。它是基于非均匀流体不可压缩Navier-Stokes方程和溶质输运方程的有限体积解。实验结果与计算结果吻合较好。受三维不稳定性影响的头部形成了一个波浪形的前线，它由大量的重流体组成，像山谷结构一样向前移动。每一个团块都是横向和向前落下的，因此它向各个方向展开，形成一个弧形锋面。它们中的一些通过压过邻近的质量而变大。扩大后的岩体再次发生不稳定，然后在其中出现一些小规模的山体。因此，洋流的前线由这些不同规模的质量的边界组成，这些边界往往相互叠加。这种三维不稳定性即使在自由滑移边界的非耗散情况下也会出现，这表明它与壁面边界层的不稳定性无关。与二维计算的对比表明，三维流动结构可能对头部后和前部密度界面的混合过程有重要贡献，并可能影响头部的速度。
The three-dimensional instability of the head of gravity currents is investigated in the experiment and in the computation of lock-exchange flow. Visualization experiments were made with dye to observe the three-dimensional features of the head advancing along an open channel with rectangular section. The computational method for gravity currents developed in the previous paper was extended to the three-dimensional cases and applied to the lock-exchange flow problem. It is based on the finite volume solution of the incompressible Navier-Stokes equation for an inhomogeneous fluid and the transport equation for solute. Agreement between the experimental and computational results is good. The head subject to the three-dimensional instability forms a wavy frontline which consists of masses of heavy fluid going ahead as a mountain- valley structure. Each of the masses falls down laterally as well as forward, and therefore it spreads out in every direction to form an arc front. Some of them become large by running over adjacent masses. The enlarged masses suffer from the instability again, and then some smaller-scale mountains appear in that. As a result, the frontline of the current consists of boundaries of these masses of different scale, often superimposed on each other. This kind of three-dimensional instability also appears even in a non-dissipative case of free-slip boundary, which indicates that it is independent of the instability of the wall boundary layer. It is shown from the comparison with the two-dimensional computation that the three-dimensional flow structure possibly makes a significant contribution to the mixing process across the density interface behind the head and at the front, which may affect the speed of the head.