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The Effect of Contaminant Drag Reduction on the Onset and Evolution of Langmuir Circulations

机译：减少污染物阻力对Langmuir循环的发生和演变的影响

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摘要

A new mechanism of instability leading to development of Langmuir circulations is proposed and studied based on the hypothesis that the turbulence and, correspondingly, the eddy viscosity are reduced in regions of higher than average contaminant concentration. Here, bubbles are considered as the contaminant, although it is known that surfactants and some particles also are capable of turbulence reduction. The analysis shows that only a very small local decrease in eddy viscosity is needed to initiate the instability. Simplifications to the momentum and bubble turbulence models, as well as neglect of vertical advection, make it possible to analytically solve the perturbation equations and determine the characteristic scale with the maximum growth rate. The scale of the fastest-growing Langmuir circulations is found to be a function of the concentration of bubbles in the near-surface layer, the surface current shear (wind shear), the Stokes drift created by the surface waves, and the eddy viscosity. In contrast to the results of earlier models, the analysis predicts that the maximum change in the current velocity along the direction of the wind (the so-called jets and wakes) is at the surface, not below it. The ratio of perturbation of along-wind surface current and vertical velocity generated by circulations (the pitch) and the aspect ratio of the Langmuir rolls are in reasonable agreement with the experimental data.
机译：提出并研究了一种新的不稳定性机制，从而导致朗缪尔环流的发展，该假设是在高于平均污染物浓度的区域中，湍流和涡流粘度会降低。尽管已知表面活性剂和一些颗粒也能够减少湍流，但是在这里气泡被认为是污染物。分析表明，涡流粘度仅需很小的局部降低即可引发不稳定性。动量和气泡湍流模型的简化，以及对流平流的忽略，使得可以解析地求解扰动方程式并确定具有最大增长率的特征尺度。发现增长最快的朗缪尔环流的规模是近表层气泡浓度，表面电流剪切（风切变），表面波产生的斯托克斯漂移和涡流粘度的函数。与早期模型的结果相反，该分析预测，当前速度沿风向的最大变化（所谓的射流和尾流）位于表面而不是表面之下。环流产生的顺风表面电流和垂直速度的摄动比（螺距）和朗缪尔辊的纵横比与实验数据基本吻合。

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  • 来源
    《Journal of Physical Oceanography》 |2014年第10期|2739-2752|共14页
  • 作者

    Basovich A.;

  • 作者单位

    Cortana Corp, 520 N Washington St,Suite 200, Falls Church, VA 22046 USA;

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