Large-scale turbulence under a solitary wave
Large-scale turbulence under a solitary wave
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孤立波下的大规模湍流
DOI：
10.1016/j.coastaleng.2005.11.004
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发表时间：
2006
影响因子：
4.4
通讯作者：
F. Ting
中科院分区：
文献类型：
--
作者：
F. Ting
研究了1：50平面坡面上破碎孤立波作用下的大尺度湍流结构。利用声学多普勒测速仪，在中浪带光滑床上方不同高度进行了三分量流速测量。实测数据表明，在水柱中部，湍流速度分量具有较好的相关性。速度关联可能是由斜涡产生的，类似于以前其他研究人员观察到的倾斜下降的涡旋。雷诺应力张量各分量相对值的垂直分布表明，湍流结构在自由面和底部之间不断演变。这种演变与二维流动结构向三维流动结构的转变以及固体底部对流动结构的影响有关。测量的湍流动能和湍流应力的时间历程显示，自由面附近的湍流事件是间歇性的，而下层的湍流更多是零星的。大型或强烈湍流事件相对于波峰点具有较短的持续时间和时间滞后。这些事件也保持了接近底部的湍流速度分量之间的良好相关性。利用立体粒子图像测速系统测量了同一跨岸位置的近底瞬时湍流速度场。这些测量表明，近床流场具有大尺度的相干流动结构，这些流动结构是大部分湍动能和湍动应力的来源。观察到的有序流动结构类型包括从上方直接下降的涡旋和下击暴流、湍流沿床面的横向扩散以及在流体流间的剪切层中形成漩涡。床层附近有组织的流动结构的一个共同特征是在纵向和横向具有较大的湍流速度，这反映了固体底部对到达床层的破碎波产生的湍流的影响。
The structure of large-scale turbulence under a broken solitary wave on a 1 in 50 plane slope was studied. Three-component velocity measurements were taken at different heights above a smooth bed in the middle surf zone using an acoustic Doppler velocimeter. The measured data showed that turbulent velocity components were well correlated in the middle part of the water column. The velocity correlations could be produced by an oblique vortex similar to the obliquely descending eddy observed previously by other investigators. The vertical distributions of the relative values of the components of the Reynolds stress tensor showed that the structure of turbulence evolved continuously between the free surface and the bottom. The evolution was related to transition from two-dimensional to three-dimensional flow structures and the effect of the solid bottom on flow structures. Time histories of measured turbulent kinetic energy and turbulence stresses showed episodic turbulent events near the free surface but more sporadic turbulence in the lower layer. Large or intense turbulent events were found to have short duration and time lag relative to the wave crest point. These events also maintained good correlations between the turbulence velocity components close to the bottom. Instantaneous turbulent velocity fields were measured near the bottom at the same cross-shore location by using a stereoscopic particle image velocimetry system. These measurements showed that the near-bed flow field was characterized by large-scale, coherent flow structures that were the sources of most of the turbulent kinetic energy and turbulence stresses. The types of organized flow structures observed included vortices and downbursts of turbulence descending directly from above, lateral spreading of turbulent fluid along the bed, and formation of vortices in shear layers between fluid streams. A common feature of the organized flow structures near the bed was the large turbulence velocities in the longitudinal and transverse directions, which reflected the influence of a solid bottom on the breaking-wave-generated turbulence arriving at the bed.