Flow and Entrainment Mechanisms Around a Freshwater Mussel Aligned With the Incoming Flow
Flow and Entrainment Mechanisms Around a Freshwater Mussel Aligned With the Incoming Flow
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DOI：
10.1029/2020wr027983
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发表时间：
2020-09
影响因子：
5.4
通讯作者：
Hao Wu;G. Constantinescu;Jie Zeng
中科院分区：
文献类型：
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作者：
Hao Wu;G. Constantinescu;Jie Zeng
本文使用来自涡解模拟的信息来表征生物体尺度上淡水贻贝周围的流动和湍流。重点是在最简单的情况下，一个部分挖洞，孤立的贻贝对齐的传入流在一个开放的渠道。研究了尾流结构和水流将贻贝从河床底质中移走并在贻贝周围引起局部冲刷的能力，它们是贻贝暴露部分高度h与贻贝总高度d之比的函数，也是来流流速U 0与来流流速之间的过滤速度比（VR）的函数，和出流虹吸管内的平均流速Ue。与流经大多数表面安装障碍物的情况相反，在这些障碍物中，床面剪切应力在物体的尾流中减小，由于水平分离剪切层内的强烈下涌运动，流在与流对齐的孤立贻贝后面引起床面侵蚀的能力相对较大。这些流动特征与不等相干性的反向旋转基涡的形成有关，这些基涡在贻贝后面引起上洗。底涡的总环量随h/d和VR的增大而增大。虽然在尾流中观察到对称和反对称脱落，但反对称模式占主导地位，并且其强度随着VR的增加而增加。作用在贝壳露出部分的无量纲流向力随h/d和VR的增大而增大。最后，本文讨论了不同h/d和VR对源自流出虹吸管的过滤水射流的动力学和稀释的影响，这对于理解贻贝如何影响混合和水质（例如，营养物的可用性和浮游植物浓度）。
The paper uses information from eddy‐resolving simulations to characterize flow and turbulence around freshwater mussels at the organism scale. The focus is on the simplest case of a partially burrowed, isolated mussel aligned with the incoming flow in an open channel. The wake structure and the capacity of the flow to displace the mussel from the bed substrate and to induce local scour around the mussel are investigated as a function of the ratio between the height of the exposed part of the mussel, h, and the total mussel height, d, and as a function of the filtration velocity ratio (VR) between the incoming channel flow velocity, U0, and the mean velocity inside the excurrent siphon, Ue. As opposed to the flow past most surface‐mounted obstacles where the bed shear stresses are reduced in the wake of the body, the capacity of the flow to induce bed erosion behind isolated mussels aligned with the flow is relatively large because of strong downwelling motions inside the horizontal separated shear layers. These flow features are associated with the formation of counterrotating base vortices of unequal coherence that induce upwash behind the mussel. The total circulation of the base vortices increases with increasing h/d and VR. Though both symmetrical and antisymmetrical shedding are observed in the wake, the antisymmetrical mode dominates, and its strength increases with increasing VR. The nondimensional streamwise force acting on the emerged part of the mussel's shell increases with increasing h/d and VR. Finally, the paper discusses the effects of varying h/d and VR on the dynamics and dilution of the jet of filtered water originating in the excurrent siphon, which is important to understand how mussels affect mixing and water quality (e.g., nutrient availability and phytoplankton concentration) in natural streams.