Turbulence in mobile-bed streams

Dey, Subhasish; Das, Ratul; Gaudio, Roberto; Bose, Sujit K.

doi:10.2478/s11600-012-0055-3

Cited by 102 publications

(39 citation statements)

References 52 publications

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“…This is typical of a stochastic process where particle concentration is closely related to that of the turbulence fluctuation arising from large eddies as shown in the work of (Liu et al, 2012). Such episodic events could occur at any location of the bed, with short periods of considerable sediment movement intermingled with long periods of negligible transport (Dey et al, 2012).…”

Section: Spectral Analysis Of Turbulence and Suspensionmentioning

confidence: 83%

“…This is evident in the turbulent "bursting" process (Kline et al, 1967; Kline, 1974, 1975), which is a critical mechanism for production of turbulent kinetic energy (Dey et al, 2012;Schoppa and Hussain, 2002). Turbulent bursting may be explained by the advection of spatially distributed vortices and structural features past a fixed point of measurement (Robinson, 1991), although this may not detect how such vortices evolve in time (Schoppa and Hussain, 2002).…”

Section: Introductionmentioning

confidence: 99%

“…The role played by bed-generated coherent eddy structures in entraining and transporting sediment particles is widely acknowledged, yet the exact mechanism is still unclear (Dey et al, 2012;Ji et al, 2013). Coherent turbulence structures have been defined, albeit reluctantly, as "connected turbulent fluid masses with instantaneously phase-correlated vorticity over their spatial extent " (1986;Hussain, 1983).…”

Section: Introductionmentioning

confidence: 99%

“…This requires prioritising research with reference to coherent flow structures and the intermittent stirring of sediments by breaking and shoaling waves, and the time-history effects of suspended sediments under irregular wave conditions [ibid.]. Understanding the spatial, temporal, and frequency characteristics of sediment suspension events in relation to turbulent fluctuations, both in structural form and in temporal distribution, is an important step towards providing a more satisfactory conceptual model for describing suspended sediment transport.The role played by bed-generated coherent eddy structures in entraining and transporting sediment particles is widely acknowledged, yet the exact mechanism is still unclear (Dey et al, 2012;Ji et al, 2013). Coherent turbulence structures have been defined, albeit reluctantly, as "connected turbulent fluid masses with instantaneously phase-correlated vorticity over their spatial extent " (1986;Hussain, 1983).…”

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confidence: 99%

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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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Section: Spectral Analysis Of Turbulence and Suspensionmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

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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“…In order to check the uncertainty associated with the ADV data, 16 pulses of 30,000 samples for a duration of 5 min each have been collected at a location 3 mm above the bed level (Table 2), where, u, v, and w are the time-averaged velocities in the streamwise, lateral, and vertical directions, respectively; u′, v′, and w′ are the fluctuating components of the instantaneous velocities in the streamwise, transverse, and vertical directions, respectively; and ðu 0 u 0 Þ 0:5 , ðv 0 v 0 Þ 0:5 , and ðw 0 w 0 Þ 0:5 are the root mean square values of u′, v′, and w′, respectively. Spikes in the velocity time series were filtered by using the acceleration threshold method (Goring and Nikora, 2002) with threshold values 1-1.5 based on trial and error (Dey et al, 2012) such that there was a satisfactory fit in the velocity power spectra with Kolmogorov's −5/3 law in the inertial subrange. Velocity power spectra (S uu (f)) for streamwise velocities of no seepage and seepage runs is shown in Fig.…”

Section: Experimental Methodologymentioning

confidence: 99%

Turbulent characteristics and evolution of sheet flow in an alluvial channel with downward seepage

2015

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Turbulent flow structures in alluvial channels with curved cross‐sections under conditions of downward seepage

Deshpande

Kumar

2016

Earth Surf Processes Landf

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Experimental investigations have been done to analyze turbulent structures in curved sand bed channels with and without seepage. Measures of turbulent statistics such as time-averaged near-bed velocities, Reynolds stresses, thickness of roughness sublayer and shear velocities were found to increase with application of downward seepage. Turbulent kinetic energy and Reynolds normal stresses are increased in the streamwise direction under the action of downward seepage, causing bed particles to move rapidly. Analysis of bursting events shows that the relative contributions of all events (ejections, sweeps and interactions) increase throughout the boundary layer, and the thickness of the zone of dominance of sweep events, which are responsible for the bed material movement, increases in the case of downward seepage. The increased sediment transport rate due to downward seepage deforms the cross-sectional geometry of the channel made of erodible boundaries, which is caused by an increase in flow turbulence and an associated decrease in turbulent kinetic energy dissipation and turbulent diffusion.

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Turbulence in mobile-bed streams

Cited by 102 publications

References 52 publications

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

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

Turbulent characteristics and evolution of sheet flow in an alluvial channel with downward seepage

Turbulent flow structures in alluvial channels with curved cross‐sections under conditions of downward seepage

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