The dynamics of strong turbulence at free surfaces. Part 2. Free-surface boundary conditions
The dynamics of strong turbulence at free surfaces. Part 2. Free-surface boundary conditions
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DOI：
10.1017/s0022112001006024
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发表时间：
2001-12
影响因子：
3.7
通讯作者：
M. Brocchini;D. Peregrine
中科院分区：
文献类型：
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作者：
M. Brocchini;D. Peregrine
水-空气自由表面上的强烈湍流可能会导致水花飞溅和一个断开的表面，就像在破碎波中一样。求平均以获得此类流动的边界条件首先需要两相区域的运动方程。这些方程是用积分方法导出的，然后得到质量和动量的平均守恒方程，以及出现额外功的湍动能方程。这些附加项既包括平均压力，也包括平均应变率，与可压缩流体有相似之处。适用于水体平均方程的边界条件是通过对两相表面层进行积分得到的。出现了许多“新”术语，必须找到其闭合表达式才能实际使用。我们对自由表面强湍流性质的了解不足以形成这样的闭合。然而，为了促进进一步的实验和理论研究，对两种简化情况进行了初步的讨论。泄漏式断路器中的大部分湍流来自于其脚部，在那里湍急的水与未受干扰的水相遇。关于断路器底部平均的讨论给出了一些参数，可以用来衡量断路器的“强度”。
Strong turbulence at a water–air free surface can lead to splashing and a disconnected surface as in a breaking wave. Averaging to obtain boundary conditions for such flows first requires equations of motion for the two-phase region. These are derived using an integral method, then averaged conservation equations for mass and momentum are obtained along with an equation for the turbulent kinetic energy in which extra work terms appear. These extra terms include both the mean pressure and the mean rate of strain and have similarities to those for a compressible fluid. Boundary conditions appropriate for use with averaged equations in the body of the water are obtained by integrating across the two-phase surface layer. A number of ‘new’ terms arise for which closure expressions must be found for practical use. Our knowledge of the properties of strong turbulence at a free surface is insufficient to make such closures. However, preliminary discussions are given for two simplified cases in order to stimulate further experimental and theoretical studies. Much of the turbulence in a spilling breaker originates from its foot where turbulent water meets undisturbed water. A discussion of averaging at the foot of a breaker gives parameters that may serve to measure the ‘strength’ of a breaker.