题目 Title

Swaying motions of submerged flexible vegetation.

期刊 Journal

Journal of Fluid Mechanics (IF=3.7)

作者 Author

Fu JH; He GJ; Huang L; Dey S; Fang HW

摘要 Abstract

Submerged vegetation plays a subtle role in exchanging the fluid mass and energy in the vegetated flow zone, where the swaying motions of flexible plants are the important source of turbulent kinetic energy production. Flume experiments were conducted to study the modes, characteristics and factors of swaying of individual submerged flexible plants. A modified plant model in a new form, representing the highly flexible vegetation with clustered leaves, was employed. A 'rigid-like' synchronous swaying mode and a 'whip-like' asynchronous flapping mode are found to appear alternately for the individual plants. The interaction between these modes depends on the resulting local flow structure affected by the plants. Compared with a plant in isolation with the same flow Reynolds number, the swaying motions of a plant within the vegetation patch are less frequent but more prone to the synchronous mode. The eigen frequency of the motions increases linearly with an increase in flow Reynolds number in the range of 2 x 10(4)-5 x 10(4), but the normalised amplitude reaches a saturation at a high flow Reynolds number. Moreover, the in-line and spanwise motions have a 2 : 1 frequency ratio for an '8' shaped trajectory on the horizontal plane and a 1 : 1 ratio for a '0' shaped circular trajectory, or a combination of both.

简介 Brief introduction

沉水植物在含植被水流的质量与能量交换中发挥着重要作用，其中柔性植物的摆动是湍动能产生的重要来源。为了研究单株沉水柔性植物的摆动模式、特征和影响因素，进行了水槽实验。采用了新型的改良植物模型——“细绳-小球”串联结构，用于概化具有簇状叶片的高度柔性植株。

研究发现，单株植物会交替出现“类刚性”同步摆动模式和“类鞭状”异步摆动模式。这两种模式之间的相互作用取决于植物影响下产生的局部流动结构。与相同流动雷诺数下的孤立植物相比，植物阵列内的植物摇摆运动频率更低，更容易出现同步的模式。在雷诺数从2 x 10(4)到5 x 10(4)的范围内，运动的特征频率随流动雷诺数的增加而线性增加，而归一化振幅在高流动雷诺数时达到饱和。此外，流向运动(x-)和展向(y-)运动的比例，对于水平面的“8”字形轨迹为2:1，而对于“0”字形轨迹为1:1，更常见的是上述两种轨迹的有机组合，形成更复杂的双重模式。

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