Fluid and sediment dynamics of upper stage plane beds

Bennett, Sean J.; Bridge, J.; Best, James L.

doi:10.1029/97jc02764

Cited by 117 publications

(108 citation statements)

References 97 publications

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“…It is also noted that the data used in the present analysis all show turbulence attenuation. Further work is obviously needed, which with higher sediment concentrations show turbulence enhancement to a greater extent than Best et al [1997] and Bennett et al [1998] for sediment effects to be accurately modeled.…”

Section: Mean Velocity Profilesmentioning

confidence: 99%

“…These are not considered here because of the likely uncertainty due to particle-particle interactions in high concentrations or to the estimations of turbulence scales over dune-covered beds. Likewise, the data of Muste and Patel [1997], Best et al [1997], and Bennett et al [1998] is neither included because of the evident fact that sediment effects in very dilute suspensions flows are too marginal to be accurately quantified.…”

Section: Laboratory Datamentioning

confidence: 99%

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Role of suspended‐sediment particle size in modifying velocity profiles in open channel flows

Cao

Egashira

Carling

2003

Water Resources Research

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.[1] Previous experimental and analytical studies have revealed that suspended particles can attenuate or enhance turbulence, depending on the particle size in relation to turbulence scales. Incorporating this mechanism, an empirical turbulent eddy viscositybased closure model is proposed for the mean velocity structure of suspended sedimentladen flow in open channels. The model integrates the sediment particle Stokes number, the ratio of particle-size-to-turbulence microscale, the ratio of particle settling velocity to bed shear velocity, and local sediment concentration. Its good performance is demonstrated in comparison with available laboratory observations. It is characterized that single-phase turbulence closure models can be adapted for sediment-laden flows by implementing sediment particle size effects.

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Section: Mean Velocity Profilesmentioning

confidence: 99%

Section: Laboratory Datamentioning

confidence: 99%

Role of suspended‐sediment particle size in modifying velocity profiles in open channel flows

Cao

Egashira

Carling

2003

Water Resources Research

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Section: Introductionmentioning

confidence: 99%

“…While ejections and sweeps reportedly occur in relatively equal proportions near the bed, the former type dominates higher in the water column (Cellino and Lemmin, 2004). Suspension of sediments is often related to large scale turbulence structures associated with clusters of ejections (Bennett et al, 1998;Kawanisi and Yokosi, 1993). Blackwelder and Kaplan, 1976;Bogard and Tiederman, 1986;Keylock, 2007;Wu and Yang, 2004), and its value is chosen arbitrarily (Keylock, 2008) or ignored altogether (Keylock et al, 2014).…”

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confidence: 99%

Wave-induced coherent turbulence structures and sediment resuspension in the nearshore of a prototype-scale sandy barrier beach

Kassem

Thompson

Amos

et al. 2015

Continental Shelf Research

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Abstract:The suspension of sediments by oscillatory flows is a complex case of fluid-particle interaction. The aim of this study is to provide insight into the spatial (time) and scale (frequency) relationships between wave-generated boundary layer turbulence and eventdriven sediment transport beneath irregular shoaling and breaking waves in the nearshore of a prototype sandy barrier beach, using data collected through the Barrier Dynamics Experiment II (BARDEX II). Statistical, quadrant and spectral analyses reveal the anisotropic and intermittent nature of Reynolds' stresses (momentum exchange) in the wave boundary layer, in all three orthogonal planes of motion. The fractional contribution of coherent turbulence structures appears to be dictated by the structural form of eddies beneath plunging and spilling breakers, which in turn define the net sediment mobilisation towards or away from the barrier, and hence ensuing erosion and accretion trends. A standing transverse wave is also observed in the flume, contributing to the substantial skewness of spanwise turbulence. Observed low frequency suspensions are closely linked to the mean flow (wave) properties. Wavelet analysis reveals that the entrainment and maintenance of sediment in suspension through a cluster of bursting sequence is associated with the passage of intermittent slowly-evolving large structures, which can modulate the frequency of smaller motions. Outside the boundary layer, small scale, higher frequency turbulence drives the suspension. The extent to which these spatially varied perturbation clusters persist is associated with suspension events in the high frequency scales, decaying as the turbulent motion ceases to supply momentum, with an observed hysteresis effect. The suspension of sediment in turbulent flows is a complex case of fluid-particle interaction, governed by shear stresses (momentum exchanges) at the bed and within the benthic boundary layer (BBL). Defining the physical processes which dictate the resuspension of sediments in coastal and estuarine settings is fundamental for accurate predictions of bed morphology evolution (Van Rijn et al., 2007), and has profound implications for the biogeochemical processes that shape their local ecology (Thompson et al., 2011). It is also a prerequisite to quantifying erosion and deposition trends, and hence guiding engineering applications such as beach nourishment, defence schemes against erosion and flooding, maintenance of marine infrastructure and waterways, and aggregate dredging. There is a genuine need for better, robust models of suspended sediment transport in the coastal zone (Aagaard and Jensen, 2013). In a vision paper on future research needs in coastal dynamics, Van Rijn et al. (2013) highlighted the pressing need for research to support such models, focusing in particular on sand transport in the shoreface (non-breaking waves), surf and swash zones; employing field and controlled laboratory experiments.The mobilisation of sediments in the nearshore and shoreface is dominated b...

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“…Van Rijn (1984) put forward the idea that the ratio of sediment diffusivity and kinematic eddy diffusivity is always greater than 1 and suggested the use of an empirical coefficient to adjust kinematic eddy diffusivity to match the vertical sediment diffusivity. However, Bennett et al (1998) attributed the disparity to the use of suspended sediment concentration profiles to calculate sediment diffusivity, and instead recommended the use of direct turbulence measurements. In general, the common consensus has been that the Rousian profile is not an appropriate surrogate for vertical sediment diffusivity.…”

Section: Introductionmentioning

confidence: 99%

Effect of self-stratification on sediment diffusivity in channel flows and boundary layers: a study using direct numerical simulations

2014

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Abstract. Sediment transport in nature comprises of bedload and suspended load, and precise modelling of these processes is essential for accurate sediment flux estimation. Traditionally, non-cohesive suspended sediment has been modelled using the advection-diffusion equation (Garcia, 2008), where the success of the model is largely dependent on accurate approximation of the sediment diffusion coefficients. The current study explores the effect of self-stratification on sediment diffusivity using suspended sediment concentration data from direct numerical simulations (DNS) of flows subjected to different levels of stratification, where the level of stratification is dependent on the particle size (parameterized using particle fall velocityṼ ) and volume-averaged sediment concentration (parameterized using shear Richardson number Ri τ ). Two distinct configurations were explored, first the channel flow configuration (similar to flow in a pipe or a duct) and second, a boundary-layer configuration (similar to open-channel flow). Self-stratification was found to modulate the turbulence intensity (Cantero et al., 2009b), which in turn was found to reduce vertical sediment diffusivity in portions of the domain exposed to turbulence damping. The effect of particle size on vertical sediment diffusivity has been studied in the past by several authors (Rouse, 1937;Coleman, 1970;Nielsen and Teakle, 2004); so in addition to the effect of particle size, the current study also explores the effect of sediment concentration on vertical sediment diffusivity. The results from the DNS simulations were compared with experiments (Ismail, 1952;Coleman, 1986) and field measurements (Coleman, 1970), and were found to agree qualitatively, especially for the case of channel flows. The aim of the study is to understand the effect of stratification due to suspended sediment on vertical sediment diffusivity for different flow configurations, in order to gain insight of the underlying physics, which will eventually help us to improve the existing models for sediment diffusivity.

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Fluid and sediment dynamics of upper stage plane beds

Cited by 117 publications

References 97 publications

Role of suspended‐sediment particle size in modifying velocity profiles in open channel flows

Role of suspended‐sediment particle size in modifying velocity profiles in open channel flows

Wave-induced coherent turbulence structures and sediment resuspension in the nearshore of a prototype-scale sandy barrier beach

Effect of self-stratification on sediment diffusivity in channel flows and boundary layers: a study using direct numerical simulations

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