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Hydraulic parameters in channels with wall vegetation and gravel bed

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International Journal of Sediment Research 2010年第1期25卷 81-90页

作者： hossein afzalimehr Razieh MOGHBEL Department of Water Engineering Isfahan University of Technology

In this experimental study,field observations and laboratory experiments have been carried out to assess the impacts of the vegetated channel walls and aspect ratio on flow velocity profiles,shear stress distribution and roughness coefficient of channel.Results show that the presence of vegetation cover on channel wall causes deviation of the Reynolds stress distribution from the linear one under uniform flow condition.It is also noticed that the Reynolds stress distribution is influenced by the aspect ratio(W/h).The vegetation cover planted on the flume wall considerably influences the location of the umax.With the changes of the position of umax,the zero Reynolds stress position also changes.The Manning coefficient n of channel with gravel bed and vegetated walls have been assessed and calculated by using the boundary layer characteristics method.

关键词： Aspect ratio Experiment Reynolds stress Roughness coefficient Vegetated channel wall Velocity profiles

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

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

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 Iran.Results 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 rivers.This 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 rivers.The 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 investigated.Two different aspect ratios of channel were used.An Acoustic Doppler Velocimetry was used to measure parameters of turbulent flow over submerged sprouts of wheat,such as velocity profiles.The 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 cover.Quadrant 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 event.Results 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 bedforms.Based on field measurements,the impacts of vegetation over bedforms on flow characteristics have been investigated.Flow velocity,Reynolds stress and turbulence intensity distributions over bedforms with vegetation have been compared with those over gravel bedforms without vegetation.By using the quadrant analysis,the dominant events of turbulent flow structures have been assessed for flows over gravel bedforms with vegetation and without vegetation.Results 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 bedforms.The change of bed roughness from gravel bed to vegetated bed causes a development of a new boundary layer.This 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 animals.Reynolds 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 bedforms.It 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 vegetation.Besides,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 cover.These 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 slopes.The distributions of velocity,Reynolds stress and turbulence intensities have been studied in this paper.Results show that as flow continues up the exit slope,the flow velocity increases near the channel bed and decreases near the water surface.The flow separation was not observed by ADV at the crest of the bed-form.In addition,the length of the separation zone increases with the increasing of entrance and exit slopes.The largest slope angle causes the maximum normalized shear stress.Based on the experiments,it is concluded that the shape of Reynolds stress distribution is generally dependent on the entrance and exit slopes of the pool.Also,the shape of Reynolds stress distribution is affected by both decelerating and accelerating flows.Additionally,with the increase in the slope angle,secondary currents are developed and become more stable.Results 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 investigated.The wavy bed was similar to dune in this study.The fixed artificial dunes were constructed over the bed and artificial vegetation put over them in a laboratory flume.An Acoustic Doppler Velocimeter and spatially-averaged method were applied to determine turbulent flow components and shear velocity.Results were compared with a gravel bedform.It was observed that vegetation cover influences considerably the flow structure and displays clearly the flow separation and reattachment point.The 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 layer.For 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,respectively.The results of laboratory study were compared with those of river study.

关键词： Wavy bed Vegetation cover Turbulence Flow separation Gravel

Reduction of local scour around bridge pier groups using collars

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International Journal of Sediment Research 2010年第4期25卷 411-422页

作者： Manouchehr HEIDARPOUR hossein afzalimehr Elham IZADINIA Department of Water Engineering Isfahan University of Technology Isfahan Iran Graduate Student of Water Engineering Isfahan University of Technology Isfahan Iran Department of Water Engineering Isfahan University of Technology Isfahan Iran

In this paper reduction of scour around group of two and three piers using circular collar has been carried out for the case of clear-water flow over uniform sediment. The efficiency of collars, with different sizes and spaces between piers is studied through experiments in group of two and three piers. The result reveals that collar has more influence in reduction of scour depth in rear piers than the first pier. Also, when the spacing between the piers increases the area without protection between the piers is washed away resulting deeper scour holes at the rear piers.

关键词： Scour Bridges Group piers Collar