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Wind and Current Effects on Extreme Wave Formation and Breaking

机译：风和电流对极端波形成和破裂的影响

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摘要

Wind and current effects on the evolution of a two-dimensional dispersive focusing wave group are investigated using a two-phase flow model. A Navier-Stokes solver is combined with the Smagorinsky subgrid-scale stress model and volume of fluid (VOF) air-water interface capturing scheme. Model predictions compare well with the experimental data with and without wind. It was found that the following and opposing winds shift the focus point downstream and upstream, respectively. The shift of focus point is mainly due to the action of wind-driven current instead of direct wind forcing. Under strong following/opposing wind forcing, there appears a slight increase/decrease of the extreme wave height at the focus point and an asymmetric/symmetric behavior in the wave focusing and defocusing processes. Under a weak following wind, however, the extreme wave height decreases with increasing wind speed because of the dominant effect of the wind-driven current over direct wind forcing. The vertical shear of the wind-driven current plays an important role in determining the location of and the extreme wave height at the focus point under wind actions. Furthermore, it was found that the thin surface layer current is a better representation of the wind-driven current for its role in wind influences on waves than the depth-uniform current used by previous studies. Airflow structure above a breaking wave group and its link to the energy flux from wind to wave as well as wind influence on breaking are also examined. The flow structure in the presence of a following wind is similar to that over a backward-facing step, while that in the presence of an opposing wind is similar to that over an airfoil at high angles of attack. Both primary and secondary vortices are observed over the breaking wave with and without wind of either direction. Airflow separates over the steep crest and causes a pressure drop in the lee of the crest. The resulting form drag may directly affect the extreme wave height. The wave breaking location and intensity are modified by the following and opposing wind in a different fashion.
机译：利用两相流模型研究了风和电流对二维色散聚焦波群演化的影响。 Navier-Stokes解算器与Smagorinsky子网格规模应力模型和流体体积（VOF）气-水界面捕获方案结合在一起。模型预测与有风和无风的实验数据都可以很好地比较。发现跟随风和相反风分别使焦点向下游和上游移动。焦点的移动主要是由于风力驱动的作用而不是直接的强迫作用。在强力追随/对立的强风作用下，焦点处的极端波高会略有增加/减少，并且在波聚焦和散焦过程中会出现不对称/对称行为。然而，在弱跟随风的作用下，由于风驱动电流对直接风力的主导作用，极端波高随着风速的增加而减小。在确定风作用下焦点处的位置和极端波高时，风力驱动电流的垂直切变起着重要作用。此外，已经发现，与先前研究使用的深度均匀电流相比，表层薄层电流由于其在风对波浪的影响中可以更好地表示风驱动电流。还研究了破碎波群上方的气流结构及其与风向波能通量的联系以及风力对破碎的影响。在跟随风的存在下的流动结构类似于在向后的台阶上的流动结构，而在相反风的存在下的流动结构与在高迎角下在翼型上的流动结构相似。在有和没有方向风的情况下，在破裂波上都可以观察到初级和次级涡旋。气流在陡峭的波峰上方分离，并在波峰的背风处引起压力下降。产生的形式阻力可能会直接影响极端的波浪高度。破浪的位置和强度会随着跟随和逆风的变化而改变。

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  • 来源
    《Journal of Physical Oceanography》 |2017年第7期|1817-1841|共25页
  • 作者

    Zou Qingping; Chen Haifei;

  • 作者单位

    Univ Maine, Dept Civil & Environm Engn, Orono, ME 04469 USA;

    Univ Maine, Dept Civil & Environm Engn, Orono, ME 04469 USA;

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