Dissipation regimes for short wind waves
Dissipation regimes for short wind waves
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短风波的耗散机制
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
G. Caulliez
中科院分区：
文献类型：
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作者：
G. Caulliez
[1]实验研究了厘米级和分米级短风浪的耗散过程。这些过程包括由于分子粘度引起的阻尼、毛细波的产生、微破碎和破碎。这些观测是在一个大型的风浪箱中进行的，使用激光片和高分辨率摄像机对各种各样的风和风进行观测。这项工作的目的是构建一个全面的图片耗散过程中的短风浪场，找到特定的耗散机制可能变得重要的尺度。已确定了四种不同的制度。对于毛细重力波场，即，对于尺度小于4cm的主导波，粘性阻尼是主要的耗散机制。主波长小于10 cm的重力-毛细波场在波峰波前处通常会出现一系列毛细波纹，但不会出现波破碎现象。对于这样的波，主要的耗散过程是通过非线性能量级联向高频运动发生的分子粘性。微尺度破碎发生在长度超过10厘米的波浪上，表现为波峰前面的非常局部的表面破裂。这些事件在水中产生湍流运动，从而增强波浪消散。当波长超过20 cm的短重力波出现时，会发生以波峰凸起、微射流撞击水面和飞溅为特征的倾入破碎。宏观溢出破碎也观察到较长的波浪在大风。在这两种情况下，从破碎波到水流的直接动量传递对波浪阻尼有显著贡献。
[1] The dissipation processes affecting short wind waves of centimeter and decimeter scales are investigated experimentally in laboratory. The processes include damping due to molecular viscosity, generation of capillary waves, microbreaking, and breaking. The observations were made in a large wind wave tank for a wide range of fetches and winds, using a laser sheet and a high-resolution video camera. The work aims at constructing a comprehensive picture of dissipative processes in the short wind wave field, to find for which scales particular dissipative mechanism may become important. Four distinct regimes have been identified. For capillary-gravity wave fields, i.e., for dominant waves with scales below 4 cm, viscous damping is found to be the main dissipation mechanism. The gravity-capillary wave fields with dominant wavelength less than 10 cm usually exhibit a train of capillary ripples at the crest wavefront, but no wave breaking. For such waves, the main dissipation process is molecular viscosity occurring through nonlinear energy cascade toward high-frequency motions. Microscale breaking takes place for waves longer than 10 cm and manifests itself in a very localized surface disruption on the forward face of the crest. Such events generate turbulent motions in water and thus enhance wave dissipation. Plunging breaking, characterized by formation of a crest bulge, a microjet hitting the water surface and a splash-up, occurs for short gravity waves of wavelength exceeding 20 cm. Macroscale spilling breaking is also observed for longer waves at high winds. In both cases, the direct momentum transfer from breaking waves to the water flow contributes significantly to wave damping.