Mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition
Mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition
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DOI：
10.1002/2013jf002858
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发表时间：
2013-12
期刊：
影响因子：
--
通讯作者：
A. Ortiz;A. Ashton;H. Nepf
中科院分区：
文献类型：
--
作者：
A. Ortiz;A. Ashton;H. Nepf
细颗粒沉积物和有机物的输运在浅水系统的营养动力学中起着重要作用，这些颗粒的命运与植被密切相关。我们描述了平均和湍流附近的圆形补丁的合成植被和研究如何连接到空间分布的悬浮泥沙沉积的流量的空间分布。刚性，紧急，灵活，沉水植被被认为是补丁，有两个不同的干密度。对于刚性挺水植被，水流调整主要是二维的，水流在水平面上偏转。水平剪切层产生了冯卡门涡列。通过补片的流动使涡街向下游移动，导致补片下游直接出现一个区域，在该区域中，平均速度和湍流速度均减小。该区域内的净沉积量增加。相比之下，对于灵活的沉水植被，流量调整是三维的，在垂直和水平面上形成剪切层。由于强烈的垂直环流，湍流动能直接在斑块下游升高。与此相一致的是，在尾流的任何一点上沉积都没有增强。这种比较表明，形态反馈不同的沉水和挺水植被。此外，增强沉积只发生在湍流和平均速度都降低的区域，相对于明渠。减少沉积（表示增强再悬浮）发生在高湍流动能的区域，无论当地的平均速度。这些观测结果突出了湍流在控制沉积方面的重要性。
The transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems, and the fate of these particles is closely linked to vegetation. We describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition. Patches of rigid, emergent, and flexible, submerged vegetation were considered, with two different stem densities. For the rigid emergent vegetation, flow adjustment was primarily two‐dimensional, with flow deflected in the horizontal plane. Horizontal shear layers produced a von Kármán vortex street. Flow through the patch shifted the vortex street downstream, resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished. Net deposition was enhanced within this region. In contrast, for the flexible, submerged vegetation, flow adjustment was three‐dimensional, with shear layers formed in the vertical and horizontal planes. Because of strong vertical circulation, turbulent kinetic energy was elevated directly downstream of the patch. Consistent with this, deposition was not enhanced at any point in the wake. This comparison suggests that morphological feedbacks differ between submerged and emergent vegetation. Further, enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced, relative to the open channel. Reduced deposition (indicating enhanced resuspension) occurred in regions of high turbulence kinetic energy, regardless of local mean velocity. These observations highlight the importance of turbulence in controlling deposition.