Effect of bed permeability and hyporheic flow on turbulent flow over bed forms
Effect of bed permeability and hyporheic flow on turbulent flow over bed forms
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DOI：
10.1002/2014gl060906
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发表时间：
2014-09-28
影响因子：
5.2
通讯作者：
Hardy, Richard J.
中科院分区：
文献类型：
--
作者：
Blois, Gianluca;Best, James L.;Hardy, Richard J.
本文使用粒子成像测速技术提供了第一次测量详细的流场在多孔床的存在下，床的形式。结果表明，透水床面上粗粒床体下游的流动与不透水床面上粗粒床体下游的流动有着本质的不同。最重要的是，背风流分离单元被从地下出现的流体射流极大地修改，使得分离流的再附着不会发生，并且限制分离区的雷诺应力基本上减小。这些结果揭示了新的光的基本流动物理和推进我们的理解与渗透床的形式相关的生态和地貌过程。水通量在床界面是至关重要的生态地球化学循环在所有的河流，但质量和动量交换床界面并不经常纳入流动模型。我们的观察表明，忽略这种交换过程中粗粒度的河流可能会忽略重要的影响。这些新的研究结果还提供了见解，以解释粗粒床的形式，在砾石中的网眼纹理的生产，并在粗砂波纹的情况下，独特的形态，所有这些都有影响的泥沙夹带和流动阻力的建模和预测。
This paper uses particle imaging velocimetry to provide the first measurements detailing the flow field over a porous bed in the presence of bed forms. The results demonstrate that flow downstream of coarse-grained bed forms on permeable beds is fundamentally different to that over impermeable beds. Most significantly, the leeside flow separation cell is greatly modified by jets of fluid emerging from the subsurface, such that reattachment of the separated flow does not occur and the Reynolds stresses bounding the separation zone are substantially lessened. These results shed new light on the underlying flow physics and advance our understanding of both ecological and geomorphological processes associated with permeable bed forms. Water fluxes at the bed interface are critically important for biogeochemical cycling in all rivers, yet mass and momentum exchanges across the bed interface are not routinely incorporated into flow models. Our observations suggest that ignoring such exchange processes in coarse-grained rivers may overlook important implications. These new results also provide insight to explain the distinctive morphology of coarse-grained bed forms, the production of openwork textures in gravels, and the absence of ripples in coarse sands, all of which have implications for modeling and prediction of sediment entrainment and flow resistance.