Interaction between open-channel flow and the wind over the surface

为了研究二次流及其对一次流的影响，系统地测量了两个纵横比为一阶的风浪池垂直横截面上平均流的垂直和水平剖面。众所周知，在风浪池中，逆压梯度由表面上的风应力平衡。然而，在本研究中，我们发现，逆压梯度也产生了二次流，其中包括一对朗缪尔涡。此外，我们还发现，在展向方向上形成了二维Poiffille流，即中心处的迎风流最小，沿沿着的迎风流最大。而不是水的粘度，这个二维Poiffille流是从动量方程通过引入与朗缪尔涡相关的涡动粘度导出的，其中涡动粘度由水在表面处的摩擦速度和罐的跨度长度的乘积给出。因此，我们建议在风浪水槽中的动量平衡方程以这样一种方式进行扩展，即压力梯度由风应力项和与朗缪尔涡相关的涡动粘性项之和来平衡。另一个有趣的发现在两个水槽中，由长宽比为1.25的大水槽和长宽比为0.75的小水槽组成，是横向平均垂直电流剖面系统地不同，他们彼此之间。我们占的原因，为什么显着不同的垂直配置文件是可能在两个风浪罐，从实验的事实，即与朗缪尔涡的垂直尺度和电流强度强烈依赖于两个纵横比和跨度长度的坦克。

Vertical and horizontal profiles of mean currents were measured systematically in vertical cross-sections of two wind-wave tanks with aspect ratio of order one to study the secondary flow and its effect on the primary flow. As is well known, in a wind-wave tank the adverse pressure gradient is balanced by the wind stress on the surface. In the present study, however, we found that the adverse pressure gradient also generated the secondary flow which consisted of a pair of Langmuir vortices. Furthermore, we found that a two-dimensional Poiseuille flow formed in the spanwise direction, that is, the minimum windward current at the center and the maximum current along the side-walls. Instead of the viscosity of water, this two-dimensional Poiseuille flow is derived from the momentum equation by introducing the eddy viscosity associated with the Langmuir vortices, where the eddy viscosity is given by the product of the friction velocity of water at the surface and the span length of the tank. Thus, we propose that the momentum balance equation in a wind-wave tank is extended in such a way that the pressure gradient is balanced by the sum of the wind stress term and the eddy viscosity term associated with the Langmuir vortices.Another interesting finding in the two tanks, which consist of a large tank with an aspect ratio of 1.25 and a small tank with 0.75, is that the lateral mean vertical current profiles were systematically different between them each other. We account for the reason why markedly different vertical profiles are possible in two wind-wave tanks, from the experimental fact that the vertical scale and current strength associated with the Langmuir vortices depend strongly on both the aspect ratio and span length of the tanks.