The coherent structures induced by a solitary wave on a smooth bed were studied in a wave flume. The solitary wave was near the point of incipient breaking and the wave Reynolds number was in the intermittent turbulent regime. The velocity field inside the bottom boundary layer was measured using a Particle Image Velocimetry (PIV) system. The bed shear stress was obtained from the measured velocities in the viscous sublayer by employing the Newton's law of viscosity. It was found that the generation and maintenance of turbulent coherent structures in a solitary wave boundary layer was like that observed in oscillatory flow boundary layers at similar wave Reynolds numbers, a process that was first described as the bursting phenomenon in the wall boundary layer of steady flows. The effect of coherent structures on the instantaneous velocity profile and bed shear stress was examined. Ejections and sweeps were found to play a crucial role in producing large bed shear stress fluctuations. Quadrant analysis and probability distribution plots of the bed shear stress showed that sweep events were responsible for producing instantaneous bed shear stress values as high as four to five times the standard deviation above the mean, while ejection events produced bed shear stress values mostly below the mean. Both types of events were more numerous than outward interaction and inward interaction . It was also found that a high proportion of the measured velocity profiles that did not follow the law of the wall were associated with large vortices in the boundary layer. It was shown that the instantaneous velocities did not conform to a law-of-the-wall velocity profile unless the measured velocity field was averaged over an area large compared to the vortices.

中文翻译：

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孤立波作用下光滑河床相干结构​​和河床剪应力的实验研究

在波槽中研究了光滑床上孤立波引起的相干结构。孤立波接近初始破裂点，波雷诺数处于间歇性湍流状态。使用粒子图像测速（PIV）系统测量底部边界层内的速度场。床剪切应力是利用牛顿粘度定律从粘性底层中测量的速度获得的。研究发现，孤立波边界层中湍流相干结构的产生和维持与在相似的波雷诺数下振荡流边界层中观察到的相似，这一过程首先被描述为稳定波边界层中的爆裂现象。流动。研究了相干结构对瞬时速度剖面和床剪切应力的影响。研究发现，喷射和扫掠在产生大床剪应力波动方面发挥着至关重要的作用。床切应力的象限分析和概率分布图表明，扫掠事件产生的瞬时床切应力值高达平均值的四到五倍标准差，而喷射事件产生的床切应力值大多低于平均值。这两类事件的数量都比外向互动和内向互动要多。研究还发现，所测量的速度分布中有很大一部分不遵循壁面定律，与边界层中的大涡有关。结果表明，除非测量的速度场在比涡流大的区域上进行平均，否则瞬时速度不符合壁面定律速度分布。