Double-Averaging Concept for Rough-Bed Open-Channel and Overland Flows: Applications

Nikora, Vladimir; McLean, S. R.; Coleman, Stephen E.; Pokrajac, Dubravka; McEwan, Ian; Campbell, Lorna Jane; Aberle, Jochen; Clunie, Dougal; Koll, Katinka

doi:10.1061/(asce)0733-9429(2007)133:8(884)

Cited by 165 publications

(120 citation statements)

References 29 publications

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“…However, according to the framework of the DA analysis for the shear stresses [Nikora et al, 2007b;Manes et al, 2007], this study indicates that the effect of seepage on the form-induced stresses is coherent with that on Reynolds stresses, that they are increased by suction and decreased by injection. The influence of latter can be so effective that the form-induced stress changes the sign within the interfacial sublayer.…”

Section: Discussionmentioning

confidence: 63%

“…Based on the intrinsic spatial averaging, the decomposition of the local time-averaged flow quantity is given by = hi +, where is the deviation of the local time-averaged flow quantity from the DA flow quantity hi. Here, the intrinsic spatial averaging, that is noted by using angle brackets h·i, is intended as an area integration over a surface parallel to the bed at variable elevation [Nikora et al, 2007a[Nikora et al, , 2007b. The is a quantity defined only over the fluid phase.…”

Section: Double-averaged Flow Fieldmentioning

confidence: 99%

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Double-averaging turbulence characteristics in seeping rough-bed streams

Dey¹,

Sarkar²,

Ballio³

2011

J. Geophys. Res.

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[1] Results of an experimental study on the effects of bed injection (upward seepage from the permeable bed) and suction (downward seepage) on the double-averaged (DA) turbulent flow characteristics over and within the interface of flow gravel beds are presented. The DA Reynolds shear stress within the interfacial sublayer undergoes a higher damping with suction and a lesser damping with injection, as compared to that with no seepage. The form-induced stress within the interfacial sublayer has a decelerating effect with no seepage and suction and an accelerating effect with injection. The quadrant analysis suggests that within the interfacial sublayer the sweep events in flows with injection and the ejection events with suction are the primary contributors toward the Reynolds shear stress production, while both the events in flows with no seepage are equally prevalent. In the roughness sublayer (form-induced and interfacial sublayers together), the mean duration of bursting increases with suction and decreases with injection, but the bursting events become less frequent with suction and more frequent with injection. The analysis of DA higher-order moments confirms that the seepage affects the Reynolds normal stress flux, the turbulent kinetic energy (TKE) flux, and the TKE budget. A downward-upstream flux of TKE is developed within the roughness sublayer with injection; while an upward-downstream flux of TKE is prevalent over the entire flow depth with suction. The significance of this study lies on the hydrodynamic process in such a physical system that may result in modifying the flow resistance, sediment entrainment, and morphological characteristics of a streambed.

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Section: Discussionmentioning

confidence: 63%

Section: Double-averaged Flow Fieldmentioning

confidence: 99%

Double-averaging turbulence characteristics in seeping rough-bed streams

Dey¹,

Sarkar²,

Ballio³

2011

J. Geophys. Res.

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“…In this paper we restrict our attention to canopies of high porosity, so we may assume n ≈ 1. For a homogeneous canopy, the resulting momentum balance is then (e.g., [48])…”

Section: Aquatic Vegetation Canopies and Momentum Balancementioning

confidence: 99%

Interaction between flow, transport and vegetation spatial structure

2008

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This paper summarizes recent advances in vegetation hydrodynamics and uses the new concepts to explore not only how vegetation impacts flow and transport, but also how flow feedbacks can influence vegetation spatial structure. Sparse and dense submerged canopies are defined based on the relative contribution of turbulent stress and canopy drag to the momentum balance. In sparse canopies turbulent stress remains elevated within the canopy and suspended sediment concentration is comparable to that in unvegetated regions. In dense canopies turbulent stress is reduced by canopy drag and suspended sediment concentration is also reduced. Further, for dense canopies, the length-scale of turbulence penetration into the canopy, δ e , is shown to predict both the roughness height and the displacement height of the overflow profile. In a second case study, the relation between flow speed and spatial structure of a seagrass meadow gives insight into the stability of different spatial structures, defined by the area fraction covered by vegetation. In the last case study, a momentum balance suggests that in natural channels the total resistance is set predominantly by the area fraction occupied by vegetation, called the blockage factor, with little direct dependence on the specific canopy morphology.

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“…However, RANS equations are not practical near hydraulically rough beds since the time averaged flow is spatially heterogeneous. To overcome the above limitation, Nikora et al (2007aNikora et al ( , 2007b proposed a double averaging methodology in which time averaged hydrodynamic equations are spatially averaged along a volume or area lying in the plane parallel to the mean bed surface. This leads to a new set of hydrodynamic equations that contain additional terms such as form-induced stresses.…”

Section: Introductionmentioning

confidence: 99%

Turbulence characteristics of flow in an open channel with temporally varying mobile bedforms

Hanmaiahgari

Roussinova

Balachandar

2016

Journal of Hydrology and Hydromechanics

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Turbulence of flow over mobile bedforms in natural open channels is not yet clearly understood. An attempt is made in this paper to determine the effect of naturally formed mobile bedforms on velocities, turbulent intensities and turbulent stresses. Instantaneous velocities are measured using a two-dimensional particle image velocimetry (PIV) to evaluate the turbulence structure of free surface flow over a fixed (immobile) bed, a weakly mobile bed and a temporally varying mobile bed with different stages of bedform development. This paper documents the vertical distribution of velocity, turbulence intensities, Reynolds shear stress and higher-order moments including skewness and turbulent diffusion factors. Analysis of the velocity distributions shows a substantial decrease of velocity near the bed with increasing bedform mobility due to increased friction. A modified logarithmic law with a reduced von Kármán constant and increased velocity shift is proposed for the case of the mobile bedforms. A significant increase in the Reynolds shear stress is observed in the mobile bedforms experiments accompanied by changes over the entire flow depth compared to an immobile bed. The skewness factor distribution was found to be different in the case of the flow over the mobile bedforms. All higher-order turbulence descriptors are found to be significantly affected by the formation of temporally varying and non-equilibrium mobile bedforms. Quadrant analysis indicates that sweep and outward events are found to be dominant in strongly mobile bedforms and govern the bedform mobility.

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Double-Averaging Concept for Rough-Bed Open-Channel and Overland Flows: Applications

Cited by 165 publications

References 29 publications

Double-averaging turbulence characteristics in seeping rough-bed streams

Double-averaging turbulence characteristics in seeping rough-bed streams

Interaction between flow, transport and vegetation spatial structure

Turbulence characteristics of flow in an open channel with temporally varying mobile bedforms

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