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flow characteristics of rectangular open channels with compound vegetation roughness

Applied Mathematics and Mechanics(English Edition) 2016年第3期37卷 341-348页

作者： Yuhong ZENG Wenxin HUAI Mingdeng ZHAO State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan University

An idealized parallel flow caused by a lateral bed roughness difference due to the partial vegetation across a channel is investigated. Similar to the flow in a compound channel, there are mixing layers adjacent to the interface between the vegetation and the non-vegetation lanes, and a lateral momentum exchange occurs between the slow- moving water in the former lane and the fast-moving water in the latter lane. Under a uniform flow condition, the three-dimensional with different discharges and water depths are （3D） instantaneous velocities of two cases measured with a 16 MHz acoustic Doppler velocimeter （micro ADV）. The longitudinal variation of the streamwise velocity and the vertical variation of the Reynolds stress are analyzed. A quadrant analysis is carried out to investigate the outward and inward interaction, ejection, and sweep phenomenon caused by the vegetation variation across the channel. The results show that the flow characteristics in the vegetation lane are similar to those in an open channel fully covered with submerged vegetation, and the flow characteristics in the smooth non-vegetation lane are similar to those in a free open channel. For the cases studied here, the width of the mixing region is about 10~ of the channel width, and the mixing region is mainly on the non-vegetation half.

关键词： vegetated flow lateral momentum exchange acoustic Doppler velocimeter(ADV) mixing layer quadrant analysis

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flow turbulence presented by different vegetation spacing sizes within a submerged vegetation patch

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Journal of Hydrodynamics 2023年第6期35卷 1131-1145页

作者： Chukwuemeka Kingsley John Jaan H.Pu Yakun Guo Prashanth R.Hanmaiahgari Manish Pandey Faculty of Engineering and Informatics University of BradfordBradfordUK Department of Civil Engineering Indian Institute of TechnologyKharagpurIndia National Institute of Technology(NIT) WarangalIndia

This study presents results from a vegetation-induced flow experimental study which investigates 3-D turbulence structure profiles,including Reynolds stress,turbulence intensity and bursting analysis of open channel *** vegetation densities have been built between the adjacent vegetations,and the flow measurements are taken using acoustic Doppler velocimeter(ADV)at the locations within and downstream of the vegetation *** different tests are conducted,where the first test has compact vegetations,while the second and the third tests have open spaces created by one and two empty vegetation slots within the vegetated *** reveals that over 10%of eddies size is generated within the vegetated zone of compact vegetations as compared with the fewer *** turbulence structures variation is also observed at the points in the non-vegetated *** findings from burst-cycle analysis show that the sweep and outward interaction events are dominant,where they further increase away from the *** effect of vegetation on the turbulent burst cycle is mostly obvious up to approximately two-third of vegetation height where this phenomenon is also observed for most other turbulent structure.

关键词： Velocity profiles acoustic Doppler velocimeter(ADV) turbulent intensities Reynolds stress turbulent bursting vegetated flow vegetation spacing sizes

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Numerical investigation of shallow wake behind a patch of rigid emergent vegetation

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Journal of Hydrodynamics 2021年第4期33卷 673-687页

作者： Jian Wang Jing-xin Zhang Dongfang Liang Lian Gan School of Naval Architecture Ocean and Civil EngineeringShanghai Jiao Tong UniversityShanghai200240China Key Laboratory of Hydrodynamics(Ministry of Education) Shanghai Jiao Tong UniversityShanghai200240China Department of Engineering University of CambridgeCambridgeUK Department of Engineering Durham UniversityDurhamUK

The shallow water flow through and around a patch of rigid emergent vegetation was investigated numerically. The mean flow field and turbulent structures were studied, especially their dependence on the solid volume fraction (SVF) of the patch and the bed friction. Two streamwise velocity scales, U1s at the starting point of the steady wake and U1e at the downstream end of the steady wake, and the length of the steady wake L1 were used to describe the steady wake behind the patch. U1s was found to be related to SVF only. However, U1e and L1 were influenced by both the SVF and the wake stability parameter S. For a sparse patch, U1e was equal to U1s, and L1 decreased with the increase of S. For a mid-dense patch, U1e was always smaller than U1s, and it increased with S and gradually approached U1s. The increase of U1e reduced the lateral velocity difference between the flows inside and outside the wake, which resulted in the increase of L1. For a highly dense patch, U1e and L1 did not increase unless S was larger than a critical value. A new parameter, r, was proposed to represent the development rate of the steady wake. The numerical results showed that r increased monotonously with S for mid-dense patches.

关键词： Shallow water vegetated flow wake bed friction

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Impact of Partially Covered Vegetation on the Lateral Velocity Distribution of Open Channel flow

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Journal of Geoscience and Environment Protection 2021年第4期9卷 1-10页

作者： Xiaonan Tang Yuxiang Hu Department of Civil Engineering Xi’an Jiaotong-Liverpool University Suzhou China

The vegetation affects the flow process and water environment, thus drawing increasing attention to river environment management. Previous research is mainly focused on flow through vegetation in a channel with fully covered single-layer vegetation. However, in natural rivers, different heights’ vegetation often co-exists along one or two sides of a river. This paper experimentally studies how the flow velocity distribution is affected by the two different-layered vegetation allocated along two sides of an open-channel. The vegetation was simulated by dowels of two heights, 10 cm and 20 cm, and arranged in a parallel pattern along two sides of a flume under partially submerged conditions. The velocities along a cross-section were measured by Acoustic Doppler Velocimetry (ADV). The results of lateral velocity distribution show that a strong shear layer exists between vegetation and non-vegetation zones, indicating the retarding effect of vegetation. Meanwhile, as the flow depth increases, the relative velocity in the free flow zone decreases compared with that in the vegetated region, indicating that vegetation resistance to the flow decreases as increasing depth under the same vegetation configuration. These ?ndings would help understand the role of multi-layered vegetation in riparian management.

关键词： vegetated flow Double-Layer Vegetation Velocity Profile Riparian Environment

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Impact of Partially Covered Vegetation on the Lateral Velocity Distribution of Open Channel flow

Impact of Partially Covered Vegetation on the Lateral Veloci...

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作者： Xiaonan Tang Yuxiang Hu Department of Civil Engineering Xi’an Jiaotong-Liverpool University

The vegetation affects the flow process and water environment, thus drawing increasing attention to river environment management. Previous research is mainly focused on flow through vegetation in a channel with fully covered single-layer vegetation. However, in natural rivers, different heights’ vegetation often co-exists along one or two sides of a river. This paper experimentally studies how the flow velocity distribution is affected by the two different-layered vegetation allocated along two sides of an open-channel. The vegetation was simulated by dowels of two heights, 10 cm and 20 cm, and arranged in a parallel pattern along two sides of a flume under partially submerged conditions. The velocities along a cross-section were measured by Acoustic Doppler Velocimetry（ADV）. The results of lateral velocity distribution show that a strong shear layer exists between vegetation and non-vegetation zones, indicating the retarding effect of vegetation. Meanwhile, as the flow depth increases, the relative velocity in the free flow zone decreases compared with that in the vegetated region, indicating that vegetation resistance to the flow decreases as increasing depth under the same vegetation *** findings would help understand the role of multi-layered vegetation in riparian management.

关键词： vegetated flow Double-Layer Vegetation Velocity Profile Riparian Environment

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