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Influence of bank vegetation and gravel bed on velocity and Reynolds stress distributions

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International Journal of Sediment Research 2009年第2期24卷 236-246页

作者： hossein afzalimehr Subhasish DEY Department of Water Engineering Isfahan University of Technology Department of Civil Engineering Indian Institute of Technology

This paper presents the results of a laboratory flume experimental study on the interaction of bank vegetation and gravel bed on the flow velocity(primarily on the location of the maximum velocity,Umax) and the Reynolds stress distributions. The results reveal that the dip of the maximum velocity below the water surface is up to 35% of flow depth and the difference between Umax and the velocity at the water surface is considerable in the presence of vegetation on the walls. The zone of the log-law varies from y/h=2 up to 15 percent of flow depth and it does not depend on distance from the wall. Deviation of the velocity profile in the outer layer over a gravel bed with vegetation cover on the walls is much larger than the case of flow over a gravel bed without vegetation cover on the walls. The presence of vegetation on the walls changes uniform flow to non-uniform flow. This fact can be explained by considering the nonlinear Reynolds stress distribution and location of maximum velocity in each profile at different distances across the flume. The Reynolds stress distributions at the distance 0.02 m from the wall have negative values and away from the wall,they change the sign taking positive values with specific convex form with apex in higher location. Average of von Karman constant κ for this study is equal to 0.16. Based on κ=0.16,the methods of Clauser and the Reynolds stress are compatible for determination of shear velocity.

关键词： Bank vegetation Uniform flow Reynolds stress Gravel bed Von Karman constant

Effect of vegetated-banks on local scour around a wing-wall abutment with circular edges

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Journal of Hydrodynamics 2014年第3期26卷 447-457页

作者： afzalimehr hossein BAKHSHI Somayeh GALLICHAND Jacques SUI Jueyi Department of Water Engineering Isfahan University of Technology Isfahan Iran Department Des Sols Et De Génie Agroalimentaire Pavillon Paul-Comtois Université Laval St-Foy QC Canada Environmental Engineering program University of Northern British Colombia Prince George BC Canada

Failure of bridges due to local scour in the vicinity of bridge abutments is a common occurrence. In this study, experiments under two different channel conditions were conducted to assess the impacts of vegetation on channel banks on local scour around a wing-wall abutment with circular edges. Some experiments were conducted in channel with vegetation on channel banks, and other experiments in channel without vegetation on channel bank. The flow velocity and Reynolds stress distributions in scour holes around a wing-wall abutment with circular edges were compared under these 2 different channel conditions. Results reveal that the vegetated-banks can reduce the time for achieving the equilibrium condition from 17 h to 9 h. Also, vegetated-bank channels can result in a significant decrease in the maximum scour depth from 0.084 m（for bare channel bank） to 0.00032 m. Additionally, around the abutment, vegetated-banks play a significant role in diminishing the Reynolds stress（RS） near the bed and removing negative values in RS distribution by weakening unfavorable pressure gradient and down-flow in the upstream of abutment.

关键词： local scour vegetated-banks wing-wall abutment circular edges Reynolds stress(RS)

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Effects of vegetation channel banks and gravel size on flow structure

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International Journal of Sediment Research 2010年第2期25卷 110-118页

作者： Elham NASIRI DEHSORKHI hossein afzalimehr Department of Water Engineering Isfahan University of Technology

Vegetation on river banks and bed roughness are important factors affecting flow structure, sediment transport, erosion and geomorphology in rivers. In this experimental study, the impacts of vegetation on flume walls, grain size of bed gravels and aspect ratio on characteristics of shear stress distribution, Coles' wake parameter, the kinematic energy correction factor (α) and the momentum correction factor (β) have been assessed. Reynolds stress distribution illustrates a three-layer pattern when the aspect ratio is smaller than 2. In addition, the aspect ratio and changes of vegetation affect α, β as well as the Coles' wake parameter Π.

关键词： Coles’ wake parameter Gravel Kinematic energy correction factor Vegetation

Characteristics of turbulent flow in 3-D pools in the presence of submerged rigid vegetation in channel bed

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Journal of Hydrodynamics 2024年第1期36卷 158-169页

作者： Kourosh Nosrati hossein afzalimehr Jueyi Sui Hamid Reza Reisifar Natural Disasters Prevention Research Center Faculty of Civil EngineeringIran University of Science and TechnologyTehranIran School of Engineering University of Northern British ColumbiaPrince GeorgeCanada

In this study,the interaction between 3-D bedforms and submerged rigid vegetation has been *** laboratory experiments were conducted to study the distribution of flow velocity,Reynolds shear stress,turbulent kinetic energy,and skewness coefficients for a constant density of *** showed that the velocity profile in the pool section deviates from those in the upstream section of the *** has been found that the dip parameter varied between 0.6H and 0.9H depending on various factors including bed roughness,vegetation distribution,and pool entrance/exit ***,scattered vegetation in the pool and differences in slopes created non-uniform flow ***,in the wake region behind each vegetated element,flow velocity reduced significantly,and small-scale eddies are formed,causing increased *** decreasing the entrance slope and bed roughness,relatively uniform flow and weaker turbulence was resulted,but the random distribution of vegetated elements counteracted this balance and intensified *** the decrease in the pool entrance slope,the contribution of sweep event decreased and the contribution of ejection event increased.

关键词： Submerged rigid vegetation 3-D pool Reynolds shear stress skewness coefficients

Field investigation on friction factor in mountainous cobble-bed and boulder-bed rivers

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International Journal of Sediment Research 2011年第2期26卷 210-221页

作者： hossein afzalimehr Jacques GALLICHAND Ehsan BAGHERI Department of Water Engineering Isfahan University of Technology Departement des sols et de genie agroalimentaire Universite Laval Water Engineering Department Isfahan University of Technology

This paper presents results of the friction factor of cobble-bed and boulder-bed rivers based on 23 field measurements in three mountainous rivers in *** reveal that features of our measured velocity profiles in boulder-bed rivers in mountainous region do not present a specific shape but illustrate specific pattern in cobble-bed *** difference is attributed to scale effect of relative submergence. It is found that the relative submergence in cobble and boulders-bed rivers is the only key parameter that influences friction factor estimation and other parameters such as particle Froude number and Froude number have few impacts on flow resistance of cobble-bed and boulder-bed *** proposed relationship for estimation for the friction factor should be useful for large coarse-bed rivers.

关键词： Boulder-bed Cobble-bed Friction factor Mountainous river Relative submergence

Investigation of turbulence characteristics in channel with dense vegetation

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International Journal of Sediment Research 2011年第3期26卷 269-280+282+281页

作者： hossein afzalimehr Razieh MOGHBEL Jacques GALLICHAND Water Engineering Department Isfahan University of TechnologyIran 84156 Departement des sols et de genie agroalimentaire Universite LavalSt-FoyQcCanada

In this experimental study,the turbulent flow in a channel with vegetation by using sprouts of wheat on channel bed was *** different aspect ratios of channel were *** Acoustic Doppler Velocimetry was used to measure parameters of turbulent flow over submerged sprouts of wheat,such as velocity *** log law and the Reynolds shear stress distribution were applied. Results indicate that the position of the maximum turbulence intensity superposes on the inflection point situated over the top of submerged vegetation *** analysis shows that near the vegetation bed,the sweeps and ejections appear to be the most dominant phenomenon,while far from the vegetated bed,the outward is dominant *** also show that the aspect ratio plays an important role on the contribution of the different bursting events for Reynolds stress determination.

关键词： Bed vegetation Aspect ratio Reynolds stress Quadrant analysis

Impacts of vegetation over bedforms on flow characteristics in gravel-bed rivers

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Journal of Hydrodynamics 2019年第5期31卷 986-998页

作者： hossein afzalimehr Mohammad Reza Maddahi Jueyi Sui Majid Rahimpour Department of Civil Engineering Iran University of Science and TechnologyTehranIran Department of Water Engineering Shahid Bahonar University of KermanKermanIran Environmental Engineering Program University of Northern British ColumbiaCanada

In the present study,among six gravel-bed river reaches,two natural gravel-bed river reaches with approximately similar bedforms and flow conditions have been found,one river reach with vegetation on bedforms and the other without vegetation on *** on field measurements,the impacts of vegetation over bedforms on flow characteristics have been *** velocity,Reynolds stress and turbulence intensity distributions over bedforms with vegetation have been compared with those over gravel bedforms without *** using the quadrant analysis,the dominant events of turbulent flow structures have been assessed for flows over gravel bedforms with vegetation and without *** show that the effect of vegetation enhances the anisotropy in turbulence and generates strong secondary currents,which lead to the occurrence of dip phenomenon at the stoss section and the crest of vegetated *** change of bed roughness from gravel bed to vegetated bed causes a development of a new boundary *** resulted in the different shape of velocity distributions over bedforms with vegetation from those over bedforms without vegetation,which can affect the lives of aquatic *** shear stress at downstream section of gravel bedform without vegetation is much higher than that of vegetated bedform,which shows that the erosion takes place from downstream of vegetated bedforms,while in the bare beds;the deposition is at downstream of *** is found that the presence of vegetation causes a chaotic distribution pattern of Reynolds shear stress,while it has more orderly pattern at the downstream section of gravel bedform without ***,the distribution of turbulence intensity in the lee side of vegetated bedform has a concave shape and in the stoss section,turbulence is generated in ejections and sweeps near the vegetation *** findings are significant to the practice of river ecological restoration.

关键词： Bedform Reynolds shear stress distribution turbulence intensity vegetation velocity profiles

Effect of slope angle of an artificial pool on distributions of turbulence

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International Journal of Sediment Research 2015年第2期30卷 93-99页

作者： Atefeh Fazlollahi hossein afzalimehr Jueyi Sui Department of Water Engineering Isfahan University of Technology Environmental Engineering Program University of Northern BritishColumbia

Experiments were carried out over a 2-dimentional pool with a constant length of 1.5 m and four different *** distributions of velocity,Reynolds stress and turbulence intensities have been studied in this *** show that as flow continues up the exit slope,the flow velocity increases near the channel bed and decreases near the water *** flow separation was not observed by ADV at the crest of the *** addition,the length of the separation zone increases with the increasing of entrance and exit *** largest slope angle causes the maximum normalized shear *** on the experiments,it is concluded that the shape of Reynolds stress distribution is generally dependent on the entrance and exit slopes of the ***,the shape of Reynolds stress distribution is affected by both decelerating and accelerating ***,with the increase in the slope angle,secondary currents are developed and become more *** of the quadrant analysis show that the momentum between flow and bed-form is mostly transferred by sweep and ejection events.

关键词： Slope angle of pool Velocity distribution Reynolds stress Quadrant analysis Secondary currents

Flow structure over a wavy bed with vegetation cover

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International Journal of Sediment Research 2017年第2期32卷 186-194页

作者： Fazeleh Kabiri hossein afzalimehr Jueyi Sui Department of Water Engineering Isfahan University of Technology Environmental Engineering Program University of Northern British Columbia 3333 University Way

On the basis of experiments carried out in flume with a wavy bed with vegetation cover,flow velocity,turbulence intensities and Reynolds stress distributions are *** wavy bed was similar to dune in this *** fixed artificial dunes were constructed over the bed and artificial vegetation put over them in a laboratory *** Acoustic Doppler Velocimeter and spatially-averaged method were applied to determine turbulent flow components and shear *** were compared with a gravel *** was observed that vegetation cover influences considerably the flow structure and displays clearly the flow separation and reattachment *** law of the wall was not valid within the vegetation cover,but it was fitted well to the zone above the vegetation cover within the inner *** a wavy bed having the same dimensions,shear velocity and friction factor over vegetation cover are 1.7 and 2.6 times of those for the gravel bedform,*** results of laboratory study were compared with those of river study.

关键词： Wavy bed Vegetation cover Turbulence Flow separation Gravel