Modeling complex flow structures and drag around a submerged plant of varied posture
Modeling complex flow structures and drag around a submerged plant of varied posture
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DOI：
10.1002/2016wr020186
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发表时间：
2017-04-01
影响因子：
5.4
通讯作者：
Marjoribanks, Timothy I.
中科院分区：
文献类型：
--
作者：
Boothroyd, Richard J.;Hardy, Richard J.;Marjoribanks, Timothy I.
虽然植被是目前在许多河流中，过去的大部分工作与植被对流量的影响建模有关，认为植被在形态上是简单的，一般忽略了自然植物的复杂性。在这里，我们报告相结合的水槽和数值模型实验，将时间平均的植物姿态，通过地面激光扫描收集，到一个计算流体动力学模型来预测周围的淹没河岸植物流。对于三个深度限制的流动条件（雷诺数= 65，000 - 110，000），植物动力学记录通过高清晰度视频图像，和数值模型进行了验证，对流速收集的声学多普勒测速仪。植物形态显示出18%的植物高度减少和14%的植物长度增加，压缩和减少体积冠层形态的雷诺数增加。植物剪切层湍流主要由剪切不稳定性产生的Kelvin-Helmholtz型涡主导，其频率估计在0.20和0.30 Hz之间，随雷诺数增加。这些结果表明，自然植物的复杂形态对流中阻力的显着影响，并允许物理确定的，物种相关的阻力系数进行计算。考虑到植被在河流廊道管理中的重要性，这里开发的方法证明了在计算植被阻力时考虑植物运动的必要性。
Although vegetation is present in many rivers, the bulk of past work concerned with modeling the influence of vegetation on flow has considered vegetation to be morphologically simple and has generally neglected the complexity of natural plants. Here we report on a combined flume and numerical model experiment which incorporates time-averaged plant posture, collected through terrestrial laser scanning, into a computational fluid dynamics model to predict flow around a submerged riparian plant. For three depth-limited flow conditions (Reynolds number = 65,000-110,000), plant dynamics were recorded through high-definition video imagery, and the numerical model was validated against flow velocities collected with an acoustic Doppler velocimeter. The plant morphology shows an 18% reduction in plant height and a 14% increase in plant length, compressing and reducing the volumetric canopy morphology as the Reynolds number increases. Plant shear layer turbulence is dominated by Kelvin-Helmholtz type vortices generated through shear instability, the frequency of which is estimated to be between 0.20 and 0.30 Hz, increasing with Reynolds number. These results demonstrate the significant effect that the complex morphology of natural plants has on in-stream drag, and allow a physically determined, species-dependent drag coefficient to be calculated. Given the importance of vegetation in river corridor management, the approach developed here demonstrates the necessity to account for plant motion when calculating vegetative resistance.