A numerical investigation into the importance of bed permeability on determining flow structures over river dunes
A numerical investigation into the importance of bed permeability on determining flow structures over river dunes
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DOI：
10.1002/2016wr019662
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发表时间：
2017-04
影响因子：
5.4
通讯作者：
S. Sinha;R. Hardy;G. Blois;J. Best;G. S. Sambrook Smith
中科院分区：
文献类型：
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作者：
S. Sinha;R. Hardy;G. Blois;J. Best;G. S. Sambrook Smith
虽然渗透性沉积物在大多数自然环境中占主导地位，但过去关于床型动力学的工作认为床是不透水的，并且通常忽略了潜流带和边界层之间的流动。在这里，我们提出了详细的数值模拟流动结果，允许评估床层渗透率对床形态动力学的影响。在可渗透的床层上模拟一个孤立的不渗透床层，结果表明水流被迫进入沙丘上游的床层，并以回流射流的形式返回到背风面的边界层，产生马蹄形涡。回流对背风面流动有明显的影响，改变了分离带，抬升了靠近分离带的剪切层远离床层。在可渗透河床上对可渗透沙丘的模拟揭示了更大的变化，因为流过沙丘的水流否定了背风面任何水流分离的形成。当两个沙丘串联在一起时，下游沙丘的流动受到上游沙丘背风面发育边界层的影响。在透水床层情况下，上升流抬升了分离出床层的流动，并通过产生的涡旋合并改变剪切层，使剪切层呈波动状而非平行于床层。这些结果表明，床层渗透性对床层形式的流动有显著影响，这可能是影响水和养分通量的关键因素。
Although permeable sediments dominate the majority of natural environments past work concerning bed form dynamics has considered the bed to be impermeable, and has generally neglected flow between the hyporheic zone and boundary layer. Herein, we present results detailing numerically modeled flow which allow the effects of bed permeability on bed form dynamics to be assessed. Simulation of an isolated impermeable bed form over a permeable bed shows that flow is forced into the bed upstream of the dune and returns to the boundary layer at the leeside, in the form of returning jets that generate horseshoe‐shaped vortices. The returning flow significantly influences the leeside flow, modifying the separation zone, lifting the shear layer adjoining the separation zone away from the bed. Simulation of a permeable dune on a permeable bed reveals even greater modifications as the flow through the dune negates the formation of any flow separation in the leeside. With two dunes placed in series the flow over the downstream dune is influenced by the developing boundary layer on the leeside of the upstream dune. For the permeable bed case, the upwelling flow lifts the separated flow from the bed, modifies the shear layer through the coalescence with vortices generated, and causes the shear layer to undulate rather than be parallel to the bed. These results demonstrate the significant effect that bed permeability has on the flow over bed forms that may be critical in affecting the flux of water and nutrients.