Transport and deposition of fine sediment in open channels with different aspect ratios

Bai, Jing; Fang, Hongwei; Stoesser, Thorsten

doi:10.1002/esp.3304

Cited by 24 publications

(13 citation statements)

References 39 publications

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“…In this study, the in‐house code Hydro3D is employed for the large‐eddy simulation (LES). Hydro3D has been validated for and applied to several flows of similar complexity to those reported here (Bomminayuni & Stoesser, ; Bai et al, ; Fraga Bugallo & Stoesser, ; Fraga Bugallo et al, ; Kara et al, ; Kim et al, ; Kara, Stoesser, & McSherry, ; Kara, Stoesser, & Sturm, ; Kim & Stoesser, ). The code is based on a finite difference method on a staggered Cartesian grid.…”

Section: Methodsmentioning

confidence: 86%

“…The streamwise turbulence intensities of profiles 0 D x to 4 D x attain their local maximum around the elevation of the boulder crest due to the shear‐layer and flow separation from the boulder and the turbulence structures evolving as a result of these. From 5 D x to 9 D x , the maximum streamwise turbulence intensity is found near the rough bed, a result of boundary layer recovery, and hence, the flow behaves more like the flow over a rough bed (Bai et al, ; Stoesser, ). The predicted profiles are generally in reasonably good agreement with the measured data.…”

Section: Resultsmentioning

confidence: 99%

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Influence of Boulder Concentration on Turbulence and Sediment Transport in Open‐Channel Flow Over Submerged Boulders

2017

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In this paper the effects of boulder concentration on hydrodynamics and local and reach‐averaged sediment transport properties with a flow over submerged boulder arrays are investigated. Four numerical simulations are performed in which the boulders' streamwise spacings are varied. Statistics of near‐bed velocity, Reynolds shear stresses, and turbulent events are collected and used to predict bed load transport rates. The results demonstrate that the presence of boulders at various interboulder spacings altered the flow field in their vicinity causing (1) flow deceleration, wake formation, and vortex shedding; (2) enhanced outward and inward interaction turbulence events downstream of the boulders; and (3) a redistribution of the local bed shear stress around the boulder consisting of pockets of high and low bed shear stresses. The spatial variety of the predicted bed load transport rate qs based on local bed shear stress is visualized and is shown to depend greatly on the boulder concentration. Quantitative bed load transport calculations demonstrate that the reach‐averaged bed load transport rate may be overestimated by up to 25 times when including the form‐drag‐generated shear stress of the immobile boulders in the chosen bed load formula. Further, the reach‐averaged bed load transport rate may be underestimated by 11% if the local variability of the bed shear stress is not accounted for. Finally, it is shown that for the small‐spaced boulder array, the bed load transport rates should no longer be predicted using a normal distribution with standard deviation of the shear stress distribution σ.

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Section: Methodsmentioning

confidence: 86%

Section: Resultsmentioning

confidence: 99%

Influence of Boulder Concentration on Turbulence and Sediment Transport in Open‐Channel Flow Over Submerged Boulders

2017

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“…The large-eddy simulation code (Hydro3D) used in this study is based on a finite volume discretization on a Cartesian grid with collocated variable arrangement [33] and has been validated thoroughly for many different flows [34][35][36][37][38][39][40][41]. The Hydro3D code solves the filtered Navier-Stokes equations for incompressible fluid flow (e.g., [42]): of the flow information available from the smallest resolved scales.…”

Section: Numerical Frameworkmentioning

confidence: 99%

Secondary Currents and Turbulence over a Non-Uniformly Roughened Open-Channel Bed

Stoesser

McSherry

Fraga

2015

Water

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Large-eddy simulations (LES) of the flow over a non-uniformly roughened channel bed are carried out to study the effect of non-uniform bed roughness on turbulence driven secondary currents and turbulence statistics. The channel bed is comprised of alternating rough and smooth strips, the width of which corresponds to the water depth. The Reynolds number based on hydraulic radius and bulk velocity is 34,000. The LES are successfully validated using experimental data. The secondary flow and bed roughness have a significant effect on the streamwise velocity and second order turbulence statistics. Turbulence is enhanced over rough strips and suppressed over smooth strips. Significant lateral momentum transfer takes place due to both advection and turbulence. The bed shear stresses over the smooth strips are approximately four times less than over the rough strips a result of near bed low momentum fluid being transported from the rough strips to the smooth strips and high momentum fluid being convected from the surface towards the bed. The most significant terms in the streamwise momentum equation are quantified and discussed with regard to momentum transfer.

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“…Although CFS have frequently been observed, a complete understanding of both their generation and evolution is limited, even though they ultimately form the nature of turbulent river flows. Furthermore, these structures contribute to both the Reynolds stresses and turbulence intensity [ Venditti et al ., ], which implies that the initiation of movement and transport of sediment will be linked to such structures [ Drake et al ., ; Hardy , ; Garcia et al ., ; Diplas and Dancy , ; Singh and Foufoula‐Georgiou , ] and they will also influence both suspended sediment [ Heathershaw , ; Bai et al ., ] and bed load [ Jackson , ; Schmeeckle et al ., ] transport. This incomplete understanding thus impedes our ability to predict the boundary layer dynamics at the microscale.…”

Section: Introductionmentioning

confidence: 99%

On the evolution and form of coherent flow structures over a gravel bed: Insights from whole flow field visualization and measurement

et al. 2016

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The microtopography of a gravel bed river has been shown to generate turbulent flow structures that originate from shear flow generated in the near-bed region. Although field and laboratory measurements have shown that such flows contain a range of coherent flow structures (CFS), the origin, evolution, and characteristics of the turbulent structures are poorly understood. Here we apply a combined experimental methodology using planar laser-induced fluorescence and particle imaging velocimetry (LIF-PIV) to measure simultaneously the geometric, kinematic, and dynamic characteristics of these CFS. The flow structures were analyzed by applying standard Reynolds decomposition and Lagrangian vortex detection methods to understand their evolution, propagation, and growth in the boundary layer and characterize their internal dynamical complexity. The LIF results identify large, individual, fluid packets that are initiated at the bed through shear that generate a bursting mechanism. When these large individual fluid packets are analyzed through direct flow measurement, they are found to contain several smaller scales of fluid motion within the one larger individual fluid parcel. Flow measurements demonstrate that near-bed shear controls the initiation and evolution of these CFS through merging with vortex chains that originate at the bed. The vortex chains show both the coalescence in the formation of the larger structures and also the shedding of vortices from the edges of these packets, which may influence the life span and mixing of CFS in open channels. The life span and geometric characteristics of such CFS are critical in influencing the duration and intensity of near-bed stresses that are responsible for the entrainment of sediment.

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Transport and deposition of fine sediment in open channels with different aspect ratios

Cited by 24 publications

References 39 publications

Influence of Boulder Concentration on Turbulence and Sediment Transport in Open‐Channel Flow Over Submerged Boulders

Influence of Boulder Concentration on Turbulence and Sediment Transport in Open‐Channel Flow Over Submerged Boulders

Secondary Currents and Turbulence over a Non-Uniformly Roughened Open-Channel Bed

On the evolution and form of coherent flow structures over a gravel bed: Insights from whole flow field visualization and measurement

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