| 摘要: |
| 波浪破碎过程产生的湍流动量和能量垂向输运对于加快海洋上混合层中垂向混合具有显著效果。采用二维实验室水槽中对波浪破碎过程进行模拟。对采集的波浪振幅时间序列采用希尔伯特变换定位破碎波位置，波浪的破碎率随有效波高的增加而增大，波浪谱分析得到的波浪基本周期与有效周期结果相似。实验中采用粒子图像测速技术（particle image velocimetry，PIV）计算波浪破碎过程中湍动能耗散率的空间分布。湍流强度与波浪的相位密切相关，波峰位置处湍流活动最为剧烈，而且波峰位置处湍流混合区内湍动能耗散率量值的垂向分布基本保持不变，即出现“湍流饱和”现象，湍流影响深度可以达到波高的70%—90%。计算湍流扩散系数的垂向分布发现，湍流扩散在混合区上部随深度的增大以指数函数的形式增加，在混合区下部趋于稳定。作为对比，在相同位置处对声学多普勒流速测量仪（acoustic Doppler velocimeter，ADV）测量的单点流速做频谱分析，发现与该位置处PIV湍动能耗散率结果量级处于同一水平，进一步验证了实验结果的准确性。 |
| 关键词: 波浪破碎 湍动能耗散率 湍流扩散系数 |
| DOI：10.11693/hyhz20200600167 |
| 分类号:P731.24 |
| 基金项目:国家重点研发计划，2016YFC1402301号；国家自然科学基金，61871353号；国家海洋局海洋溢油鉴别与损害评估技术重点实验室基金课题，201604号。 |
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| TURBULENT MIXING DURING WAVE BREAKING: AN EXPERIMENTAL STUDY |
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MU Hai-Di1, LIU Yun-Long2, YUAN Yuan2, JU Lian2, LIU Juan3, MENG Jing4, CHEN Xu1
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1.Key Laboratory of Physical Oceanography, Ocean University of China, Qingdao 266003, China;2.North China Sea Environmental Monitoring Center, State Oceanic Administration, Qingdao 266033, China;3.Beijing Institute of Applied Meteorology, Beijing 100029, China;4.College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao 266100, China
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| Abstract: |
| The vertical transport of turbulent momentum and energy generated by wave breaking has a significant effect on accelerating vertical mixing in the mixing layer of the upper ocean. The wave breaking process was simulated in a two-dimensional laboratory flume. Hilbert transform was used to locate the position of breaking wave in the sampled wave amplitude time series. The breaking rate of wave increased with the increase of effective wave height. The wave basic period obtained by wave spectrum analysis was similar to that of effective period. With the increase in significant wave height, the wave breaking rate increased in square form, and the wave spectra show that the wave periods were similar to the significant wave heights. The spatial distribution of the turbulent kinetic dissipation rate was calculated from the data of particle image velocimetry (PIV). The observations showed that the phase of wave had a close relationship with turbulence intensity, reaching maximum at wave crest. The phenomenon that the vertical profile of the turbulent dissipation rate stayed unchanged in the upper crest layer was called "turbulence saturation" and the turbulence by wave breaking reached 70%-90% of the depth of wave height. The calculation of the turbulent diffusivity coefficient increased exponentially with depth in the upper ocean layer and then stabilized. The data collected from the acoustic Doppler velocimeter (ADV) was compared with that of the PIV at the same location, and showed the same magnitude. Therefore, the results of the experiments show high accuracy for turbulence. |
| Key words: wave breaking turbulent kinetic dissipation rate turbulent diffusivity coefficient |
