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Large eddy simulation study of a wave-induced shallow-water monopolar vortex
Ocean Modelling ( IF 3.2 ) Pub Date : 2021-03-26 , DOI: 10.1016/j.ocemod.2021.101796
Yeulwoo Kim , Nikos Kalligeris , Tian-Jian Hsu , Patrick J. Lynett

Detailed flow and turbulence characteristics of a long-wave-induced shallow-water monopolar vortex are investigated using a 3D large eddy simulation. The numerical model is validated with measured data where nearly 2D shallow turbulent coherent structures were generated by sending a single asymmetric wave through a harbour channel in a large 3D wave basin. Model results demonstrate that the vortex centre trajectory is sensitive to small perturbations applied via a surface tension coefficient. Instantaneous model results are averaged over three numerical runs with slightly different surface tension coefficients so that a sufficient number of realisations are obtained for ensemble-averaging. Because of shallow water depth, flow fields are dominated by a horizontally rotating current and vertically suppressed velocities resembling quasi-2D flow conditions. Bed shear stress calculated using the decay of peak azimuthal velocity is qualitatively similar to that obtained using a near-wall modelling method. Although 2D turbulent coherent structures evolve into monopolar vortices at later stages, flow is not completely axisymmetric due to secondary turbulent coherent sub-structures located in the middle of the water column and away from the core. Turbulence production and turbulence dissipation rate demonstrate a local imbalance where turbulence is mainly produced by flow shear correlated with recirculation patterns, while turbulent kinetic energy is predominantly dissipated near the no-slip bottom boundary. While the free surface elevation at the vortex core indicates an upwelling pattern consistent with laboratory experiments, model results show evidence that the recirculation pattern is influenced by a low frequency resonant mode of the wave basin.



中文翻译:

波浪引起的浅水单极涡旋的大涡模拟研究

使用3D大涡模拟研究了长波诱发的浅水单极涡旋的详细流动和湍流特性。该数值模型通过实测数据进行了验证,其中通过在大型3D波浪盆地中通过港口通道发送单个不对称波,生成了近2D浅湍流相干结构。模型结果表明,涡旋中心轨迹对通过表面张力系数施加的微小扰动敏感。瞬时模型结果在表面张力系数略有不同的三个数值运行中进行平均,以便获得足够数量的实现以进行集合平均。由于水深浅,流场由水平旋转的电流和垂直抑制的速度(近似于二维流条件)主导。使用峰值方位角速度的衰减计算得出的床层剪应力在质量上与使用近壁建模方法获得的相类似。尽管二维湍流相干结构在后期阶段演变成单极涡流,但由于次级湍流相干子结构位于水柱中部且远离岩心,因此流动不是完全轴对称的。湍流产生和湍流耗散率显示出局部失衡,其中湍流主要是由与再循环模式相关的流动剪切产生的,而湍流动能则主要消散在防滑底部边界附近。

更新日期:2021-04-15
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