Influence of Turbulence on Bed Load Sediment Transport

Sumer, B. Mutlu; Chua, Leok Poh; Cheng, Nian‐Sheng; Fredsøe, Jørgen

doi:10.1061/(asce)0733-9429(2003)129:8(585)

Cited by 214 publications

(171 citation statements)

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“…Typical factors causing this non-uniformity and/or intermittency can include local variations in bed slope or bed geometry, 6,7 obstacles within the flow, 8 and the presence or development of intermittent coherent vortex structures in the near-bed region. [9][10][11][12] Under these conditions, the near-bed turbulence is no longer necessarily correlated with the mean flow characteristics, and so the parametric relations for sediment transport quantities, based on steady uniform flows, can often provide poor comparisons with experiment data.…”

Section: Introductionmentioning

confidence: 99%

“…[9][10][11][12] Under these conditions, the near-bed turbulence is no longer necessarily correlated with the mean flow characteristics, and so the parametric relations for sediment transport quantities, based on steady uniform flows, can often provide poor comparisons with experiment data. 8 As noted by Schmeeckle et al, 13 improvements in our understanding of the sediment transport process, in general, requires a detailed knowledge of how turbulent fluctuations in the near-bed region interact with and displace sediment grains. Attempts have been made to address this issue using novel experiments performed in steady channel flows: See, for example, the channel-flow experiments reported by Sumer et al 8 who used an array of grids placed at different heights along the channel to vary the near-bed turbulence intensity.…”

Section: Introductionmentioning

confidence: 99%

“…8 As noted by Schmeeckle et al, 13 improvements in our understanding of the sediment transport process, in general, requires a detailed knowledge of how turbulent fluctuations in the near-bed region interact with and displace sediment grains. Attempts have been made to address this issue using novel experiments performed in steady channel flows: See, for example, the channel-flow experiments reported by Sumer et al 8 who used an array of grids placed at different heights along the channel to vary the near-bed turbulence intensity. However, it is also necessary for researchers to consider different types of turbulent flow, with attention focussed on the role played by turbulent fluctuations.…”

Section: Introductionmentioning

confidence: 99%

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Threshold criteria for incipient sediment motion on an inclined bedform in the presence of oscillating-grid turbulence

Mohtar

Munro

2013

Physics of Fluids

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A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. Here, we report laboratory experiments to investigate the threshold criteria for incipient sediment motion in the presence of oscillating-grid turbulence, with the bed slope inclined at angles between the horizontal and the repose limit for the sediment. A set of nine mono-disperse sediment types was used with size ranges normally associated with either the hydraulically-smooth or transitional regimes. Measurements of the (turbulent) fluid velocity field, in the region between the grid and bedform's surface, were obtained using two-dimensional particle imaging velocimetry. Statistical analysis of the velocity data showed that the turbulence had a anisotropic structure, due to the net transfer of energy from the normal to the tangential velocity components in the near-bed region, and that the fluctuations were dominant compared to the secondary mean flow. The sediment threshold criteria for horizontal bedforms were compared with, and found to be in good qualitative agreement with the standard Shields curve. For non-horizontal bedforms, the bed mobility was found to increase with increasing bed slope, and the threshold criteria were compared with previously-reported theoretical models, based on simple force-balance arguments. C 2013 American Institute of Physics. [http://dx

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Threshold criteria for incipient sediment motion on an inclined bedform in the presence of oscillating-grid turbulence

Mohtar

Munro

2013

Physics of Fluids

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“…Hence, the integral parameter used in standard models is the time-averaged mean bed shear stress, [1][2][3][4] with the effects due to turbulent fluctuations considered implicitly. However, in many naturally occurring flows, for which the simplifications of uniformity and stationarity no longer hold, the intensity of turbulent fluctuations in the near-bed region can vary significantly with bed position and time due to factors such as external turbulence generated by flow obstacles, 5 local bed geometry, 6,7 or intermittent bursting and ejection events associated with the development of coherent vortex structures within the near bed region. 8 In such flows, the near-bed turbulence no longer scales with the mean flow characteristics.…”

Section: Introductionmentioning

confidence: 99%

“…8 In such flows, the near-bed turbulence no longer scales with the mean flow characteristics. Indeed, laboratory experiments 5 have reported up to a factor of six increase in the sediment transport rate for a class of steady open channel flow in which the mean bed shear stress was kept fixed, but with the near-bed turbulence intensity increased by 20% (using an array of grids placed at different heights within the flow). Clearly, clarification of the complex and intermittent turbulence-sediment interaction in the near-bed region is required.…”

Section: Introductionmentioning

confidence: 99%

The interaction of a vortex ring with a sloped sediment layer: Critical criteria for incipient grain motion

Munro

2012

Physics of Fluids

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Experiments were performed to analyse the interaction between a vortex ring and a sloped sediment layer. Attention focussed on interactions under “critical” conditions, in which sediment motion was only just induced by the ring's flow field. Both hydraulically smooth and hydraulically rough bedforms were analysed, using near-spherical monodisperse sediments with relative densities of 1.2 and 2.5 and mean diameters (dp) ranging between 80 and 1087 μm. Measurements of the vortex-ring flow field were obtained, during the interaction, using two-dimensional particle imaging velocimetry. The threshold conditions for incipient sediment motion were analysed in terms of the critical Shields parameter (Nc), defined in terms of the peak tangential velocity measured adjacent to the bed surface. Bed-slope effects were investigated by tilting the sediment layer at various angles between the horizontal and the repose limit for the sediment. In all cases, the propagation axis of the vortex ring was aligned normal to the bed surface. The measured values of Nc were compared with a force-balance model based on the conditions for incipient grain motion on a sloping bed. For hydraulically smooth bedforms, where the bed roughness is small compared to the boundary-layer depth, the model was derived to account for how viscous stresses affect the drag and lift forces acting on the near surface sediment. For hydraulically rough bedforms, where this viscous-damping effect is not present, the model assumes the drag and lift forces scale with the square of the near-bed (inviscid) velocity scale. In both cases, the model predicts that bedforms become more mobile as the bed slope is increased. However, the damping effect of the viscous sublayer acts as a stabilizing influence for hydraulically smooth bedforms, to reduce the rate at which the bed mobility increases with bed slope. The measured values of Nc were in agreement with the trends predicted by this model, and exhibit a transition in behaviour between the smooth-bed and rough-bed cases when dp/δs ≈ 20 (where δs is the viscous-sublayer length scale).

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Laboratory observations of flow and sediment transport induced by plunging regular waves

Sumer

Güner

Hansen

et al. 2013

J. Geophys. Res. Oceans

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[1] Two parallel experiments involving the evolution and runup induced by plunging regular waves near the shoreline of a sloping bed are considered: (1) a rigid-bed experiment, allowing direct (hot film) measurements of bed shear stresses and (2) a sediment-bed experiment, allowing for the measurement of pore-water pressures as well as observation of sediment suspension and bed morphological changes. Both experiments utilize the same initial bed profile and wave forcing. The experiments show that the mean bed shear stresses experienced onshore of incipient breaking are amplified by nearly a factor of 2 relative to prebreaking conditions, whereas their corresponding turbulent fluctuations are amplified even more strongly, by a factor of 5-6. The plunging processes lead to a series of vortices, whose formation may be explained as the result of shear layer instability. Measurements show that these vortices can significantly enhance peaks in the offshoredirected bed shear stresses. Moreover, near-bed pore pressure measurements indicate that these vortices cause large upward-directed pressure gradients, which in turn produce a corresponding series of suspended sediment plumes shoreward of the initial breaking event. These findings are related to the induced morphological changes over both short and long time scales. The present results are also compared and contrasted with previous experiments utilizing a similar methodology, but involving plunging solitary waves.

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Influence of Turbulence on Bed Load Sediment Transport

Cited by 214 publications

References 19 publications

Threshold criteria for incipient sediment motion on an inclined bedform in the presence of oscillating-grid turbulence

Threshold criteria for incipient sediment motion on an inclined bedform in the presence of oscillating-grid turbulence

The interaction of a vortex ring with a sloped sediment layer: Critical criteria for incipient grain motion

Laboratory observations of flow and sediment transport induced by plunging regular waves

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