A numerical investigation of lutocline dynamics and saturation of fine sediment in the oscillatory boundary layer
A numerical investigation of lutocline dynamics and saturation of fine sediment in the oscillatory boundary layer
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DOI：
10.1029/2011jc007185
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发表时间：
2011-09
影响因子：
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通讯作者：
C. Ozdemir;T. Hsu;S. Balachandar
中科院分区：
文献类型：
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作者：
C. Ozdemir;T. Hsu;S. Balachandar
[1] 了解泥质海底的状态对于沉积物输送、水动力耗散和海底特性至关重要。然而，这一努力具有挑战性，因为泥泞环境中沉积物的可用性和沉降速度变化很大。对于给定的雷诺数（中等能量泥质陆架中细粒沉积物沉降的典型特征），最近的 3D 数值模拟揭示了波浪引起的细粒沉积物迁移的四种不同模式。这些状态取决于沉积物的可用性（或浓度），范围从充分混合条件到叶绿素的形成，并最终形成完全的流动层流。通过保持沉积物可用性不变，这项研究进一步证明了在一定范围的沉积物沉降速度下这些流态的存在。模拟结果表明，当沉降速度较大时，卢斜线的位置变低（更靠近床层），并且当沉降速度进一步增加时，流动最终层流化。因此，卢托克林的动力学显然与这些流动状态之间的转变有关。通过沉积物通量和湍流动能的预算揭示了叶绿素存在下的垂直流动结构。从一个新的角度，即湍流悬浮和浓度波动方差的预算，进一步说明了卢斜层中的抑制混合。饱和度的概念通常用于潮汐边界层，在这里扩展到波浪边界层。
[1] Understanding the state of the muddy seabed is critical to sediment transport, hydrodynamic dissipation and seabed properties. However, this endeavor is challenging because the availability and settling velocity of sediment in muddy environments are highly variable. For a given Reynolds number, typical of fine sediment settling in a moderately energetic muddy shelf, recent 3D numerical simulations have revealed four distinct regimes of wave-induced fine sediment transport. These regimes depend on the availability (or concentration) of sediment and range from well-mixed condition to the formation of lutocline, and eventually a complete flow laminarization. By keeping the sediment availability unchanged, this study further demonstrates the existence of these flow regimes for a range of sediment settling velocities. Simulation results suggest that when settling velocity is larger, the location of the lutocline becomes lower (closer to the bed) and the flow eventually laminarizes when there is further increase in the settling velocity. Hence, the dynamics of lutocline is clearly related to the transition between these flow regimes. The vertical flow structure in the presence of lutocline is revealed through the budgets of sediment flux and turbulent kinetic energy. The suppressed mixing in the lutocline layer is further illustrated from a new perspective, i.e., the budgets of turbulent suspension and concentration fluctuation variance. The concept of saturation, commonly used for tidal boundary layer, is extended here for wave boundary layer.