题目 Title

Influence of submerged flexible vegetation on turbulence in an open-channel flow.

期刊 Journal

Journal of Fluid Mechanics (IF=4.245)

作者 Author

Wang JY; He GJ; Dey S; Fang HW

摘要 Abstract

In this study, we present a three-dimensional numerical model for the interaction of flow with submerged flexible vegetation, based on a large-eddy simulation and the immersed boundary method. The model innovatively realises the interaction between the flow and highly flexible vegetation with clustered leaves. Besides being a three-dimensional model of motion with full degrees of freedom, this study improves the consideration of the motion of the vegetation in all directions, and in addition the energy and momentum transfer in the spanwise direction. Furthermore, we perform a flume experiment for the flow with submerged flexible vegetation, the results of which are used to validate the simulation effects of the numerical model. It is found that the numerical model can effectively simulate the velocity profiles and the movement of vegetation induced by the flow. Using the model to analyse the flow-vegetation interaction, we find that the movement of vegetation is closely related to the flow velocity. As the flow velocity increases, both the offset angle and the vegetation swaying amplitude increase. Compared to vertical rigid vegetation, the tilting of flexible vegetation does not significantly change the velocity difference and the magnitude of the turbulent kinetic energy between the inside and the outside of the vegetation canopy, but it does weaken the disturbance to flow, thus reducing the resistance to flow. However, the swaying of vegetation dose significantly increase the velocity difference between the inside and the outside of the canopy. It forms Kelvin-Helmholtz hairpin vortices intensifying the turbulence production, and enhancing the disturbance and resistance to flow.

简介 Brief introduction

本研究提出了一个基于大涡模拟（LES）和浸没边界法（LBM）的水流与沉水柔性植被相互作用的三维数值模型，创新性地实现了水流与具有团簇状叶片的高柔性植被间相互作用的模拟。该模型是一个能实现植被全自由度运动的三维模型，能够计算植被在各个方向上的运动以及在展向上的物质、动量输移。研究发现：植被的运动与流速密切相关——随着流速的增加，植被的倾斜角和摆动幅度均有所增加。与垂直的刚性植被相比，柔性植被的倾斜没有显著改变植被冠层内外的流速差和湍动能的大小，但它削弱了对水流的干扰，进而减少了对水流的阻力。然而，植被的摆动显著增加了冠层内外的速度差，形成了Kelvin-Helmholtz-发夹涡结构，加剧了水流的湍动，进而增加了对水流的阻力。

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