On the transport modes of fine sediment in the wave boundary layer due to resuspension/deposition: A turbulence‐resolving numerical investigation
On the transport modes of fine sediment in the wave boundary layer due to resuspension/deposition: A turbulence‐resolving numerical investigation
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DOI：
10.1002/2014jc010623
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发表时间：
2015-03
影响因子：
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通讯作者：
Zhen Cheng;Xiao Yu;T. Hsu;C. Ozdemir;S. Balachandar
中科院分区：
文献类型：
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作者：
Zhen Cheng;Xiao Yu;T. Hsu;C. Ozdemir;S. Balachandar
以前的野外观测表明，波浪边界层是将细颗粒沉积物从近岸输送到大陆架的主要管道之一。最近，一系列湍流解析模拟进一步证明，由于泥沙可利用性所控制的不同程度的泥沙引起的密度分层，存在着一系列的流型。在这项研究中，我们研究了泥沙有效性受来自/向床面的再悬浮/沉积的影响。具体地说，我们重点讨论了侵蚀的临界剪应力和沉降速度如何决定输运方式。模拟结果表明，在一定的波强下，泥质陆架能量较大，沉积速度约为0.5 mm/S，随着冲刷临界剪应力的降低，泥质陆架的输送方式有三种，即均匀混合输送(模式I)、类双层输送并形成黄跃层(模式II)和层状输送(模式III)。此外，沉降速度的降低也会导致运输方式的类似转变。我们还证明，分层的开始可以很好地解释，由于沉积物的减弱湍流，波平均底部应力降低到约0.39Pa.提出了一种二维参数映射来描述从一种输运模式到另一种输运模式的转变，它是在固定波强下临界剪应力和沉降速度的函数。
Previous field observations revealed that the wave boundary layer is one of the main conduits delivering fine sediments from the nearshore to continental shelves. Recently, a series of turbulence-resolving simulations further demonstrated the existence of a range of flow regimes due to different degrees of sediment-induced density stratification controlled by the sediment availability. In this study, we investigate the scenario in which sediment availability is governed by the resuspension/deposition from/to the bed. Specifically, we focus on how the critical shear stress of erosion and the settling velocity can determine the modes of transport. Simulations reveal that at a given wave intensity, which is associated with more energetic muddy shelves and a settling velocity of about 0.5 mm/s, three transport modes, ranging from the well-mixed transport (mode I), two-layer like transport with the formation of lutocline (mode II), and laminarized transport (mode III) are obtained as the critical shear stress of erosion reduces. Moreover, reductions in the settling velocity also yield similar transitions of transport modes. We also demonstrate that the onset of laminarization can be well explained by the reduction of wave-averaged bottom stress to about 0.39 Pa due to attenuated turbulence by sediments. A 2-D parametric map is proposed to characterize the transition from one transport mode to another as a function of the critical shear stress and the settling velocity at a fixed wave intensity.