An experimental study on CL2 mechanism of Langmuir circulation

为了解风浪作用下的波流相互作用，已进行了室内试验。主要目的是回答以下问题。在风箱中，巨浪如何与风驱动的水流相互作用？为了验证Craik(1977)和Leibovich(1977)提出的CL2机制的有效性，研究了涌浪(单色机械波)对地下流动的影响。为了探讨风生水流对机械波的响应，我们使用了两组机械波：一组称为顺风涌浪(情形FS)，另一组称为逆风涌浪(情形OS)。为此，在7-8m/s的恒定风速作用下，利用双分量激光测速仪对FS和OS两组涌浪的垂直和横向截面进行了系统和详细的测量。当传播直接…时，在池流中发现了强烈的波流相互作用更多的机械波离子(波频=1赫兹，起始波幅度H0=2.5 cm)被逆转。首先，对于情况OS，机械波加速了储罐内的初级环流，但对一对二维(垂直)朗缪尔环流(2D-LC)略有衰减。第一，垂直环流对单色涌浪的响应符合CL2机制，即2D-LC受到顺风涌浪的增强，而受到逆风涌浪的减弱。特别指出，尾随风涌引起了整个流动的剧烈湍流混合，导致一次环流减速，这似乎是CL2机制的特征；其次，在FS情形下，涌浪引起的雷诺切应力为负值，而在OS情形下则为正应力。这一事实似乎与情况FS的减速和情况OS的初级环流的加速密切相关。也就是说，当膨胀诱导的雷诺切应力分别为正和负时，我们可以得出结论，它在初级环流的加速和减速中起着重要的作用。较少

Laboratory experiments have been undertaken to understand the wave-current interaction under the wind waves. The primary purpose is to answer the following question. How do swell waves interact with the wind-driven current in a wind tank? The effects of swell (monochromatic mechanical waves) on the subsurface flow were examined to test the validity of the CL2 mechanism proposed by Craik (1977) and Leibovich (1977). In order to explore the response of the wind-driven flow to mechanical-waves, we used two sets of mechanical waves : One is referred to as the wind-following swell (case FS), and the other the wind-opposing swell (case OS). For this purpose, a vertical cross-sectional plane normal to the wind was systematically and in detail measured both vertically and laterally using a two-component LDV in each of the 2 sets of swell cases of FS and OS under the action of a constant wind speed of 7-8 m/s.A strong wave-current interaction was found in a tank flow when the propagation direct … More ion of mechanical-waves (wave frequency = 1Hz, initial wave amplitude H_0 = 2.5 cm) was reversed. First, for case OS the mechanical-waves highly speeded up the primary circulation in the tank but slightly decayed a pair of 2-dimensional (vertical) Langmuir circulation (2D-LC). Second, for case AS they dramatically slowed down the primary circulation, but enhanced the 2D-LC, leading to the generation of vigorous vertical mixing.First, it is found that the response of the vertical circulation to the monochromatic swell wave is consistent with the CL2 mechanism ; that is, the 2D-LC is enhanced by the wind-following swell but attenuated by the wind-opposing swell. In particular, it tamed out that the wind-following swell caused vigorous turbulent mixing in the whole flow, leading to the slowdown of the primary circulation, which appears to be characteristic of the CL2 mechanism.Second, the swell-induced Reynolds shear stress was negative in case FS but became positive in case OS. This fact appears to be closely related to the slowdown in case FS and the speedup in case OS of the primary circulation. That is, we may conclude that the swell-induced Reynolds shear stress plays an important role in the acceleration and deceleration of the primary circulation, when it is positive and negative, respectively. Less