Non-universality of von Kármán's κ in fluvial streams

Gaudio, Roberto; Miglio, Antonio; Dey, Subhasish

doi:10.1080/00221686.2010.507338

Cited by 73 publications

(33 citation statements)

References 19 publications

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“…They reported a reduction of j that could be expressed by a non-linear function of the bedload volume concentration. [13] performed a review of previous work on the characterisation of the vertical profile of the mean longitudinal velocity to highlight the fact that there is no necessary argument for the universality of the van Kármán constant and that there exists a substantial number of databases whose interpretation favours the hypothesis of a reduction of the value of j with sediment transport.…”

Section: Introductionmentioning

confidence: 99%

The von Kármán constant for flows over rough mobile beds. Lessons learned from dimensional analysis and similarity

Ferreira

2015

Advances in Water Resources

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Section: Introductionmentioning

confidence: 99%

The von Kármán constant for flows over rough mobile beds. Lessons learned from dimensional analysis and similarity

Ferreira

2015

Advances in Water Resources

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“…Dey and Raikar (2007) studied the turbulence characteristics in flows over gravel beds near the threshold. They obtained the von Kármán constant as 0.35, which was different from its traditional value of 0.41 (also see Gaudio et al 2010). Despite a number of serious efforts, there remain a lot of unanswered questions in quantifying the bursting events related to sediment entrainment and the role of near-bed turbulence on sediment threshold.…”

Section: Introductionmentioning

confidence: 99%

Near-Bed Turbulence Characteristics at the Entrainment Threshold of Sediment Beds

2011

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This experimental study is devoted to quantification of the near-bed turbulence characteristics at an entrainment threshold of noncohesive sediments. Near the bed, the departure in the distributions of the observed time-averaged streamwise velocity from the logarithmic law is more for immobile beds than for entrainment-threshold beds. In the Reynolds shear stress distributions, a damping that occurs near the bed for sediment entrainment is higher than that for immobile beds. Quadrant analysis reveals that in the near-bed flow zone, ejections and sweeps on immobile beds cancel each other, giving rise to the outward interactions, whereas sweeps are the dominant mechanism toward sediment entrainment. The bursting duration for entrainment-threshold beds is smaller than that for immobile beds. On the other hand, the bursting frequency for entrainment-threshold beds is larger than that for immobile beds. The third-order correlations indicate that during sediment entrainment, a streamwise acceleration associated with a downward flux and advection of streamwise Reynolds normal stress is prevalent. The streamwise and the downward vertical fluxes of turbulent kinetic energy (TKE) increase with sediment entrainment. The TKE budget proves that for sediment entrainment, the pressure energy diffusion changes drastically to a negative magnitude, indicating a gain in turbulence production.

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“…In hydraulically rough flow, which is universal in bedrock rapids, the parameter z o is a bed roughness length scale and k, the von Kármán constant, can reasonably be set to equal 0.4 in deep rivers where the suspended sediment load is small (Smart, 1999;Gaudio et al, 2010). Only profile fits with r 2 values greater than 0.60 were considered to be acceptable within the Results section.…”

Section: Theoretical Velocity Profile Functionsmentioning

confidence: 99%

Flow structure in large bedrock‐channels: The example of macroturbulent rapids, lower Mekong River, Southeast Asia

Carling

Huang

et al. 2018

Earth Surf Processes Landf

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The rate of bedrock channel incision is key to the understanding of landscape evolution. Theoretical models relate channel incision to sediment transport; the latter conditioned by the bed shear stress. However, theory is deficient in an appreciation of the transverse and vertical flow structure that mediates shear stress for deep, narrow inner‐channels, which often characterize large bedrock rivers. Here we present the detail of the structure of high Reynolds number flows for bedrock‐controlled rapids of the Mekong River, SE Asia. Distinct filaments of high‐velocity flow, separated by regions of slower flow, occur across channels; the numbers of filaments scale linearly with channel width to maximum‐depth (B/hmax) ratios. Inner‐channels with low ratios (B/hmax < 20) exhibit wall‐effected flow structure. Effects include suppressed maximum velocity filaments due to: (i) significant channel‐transverse flow; (ii) strongly‐sheared vertical flow structure; and (iii) significant underflows. Such complex water column flow patterns largely defy theoretical description. Nonetheless near the bed, the vertical velocity distributions often conform to: (i) ‘law‐of‐the‐wall’ logarithmic theory; or (ii) profiles in the near‐bed region and within the transition to outer flow can be described using a log‐wake function. Consequently, for selected velocity profiles it is possible to derive hydraulic parameters suitable for input to incision models. Chezy‐C values are high, indicating low flow resistance, while bed shear stresses remain competent, even during low‐discharges, to transport cobble bedload across low roughness bedrock surfaces. Thus, as competence is high, no blanketing sediment deposits can develop within inner channels to prevent bedrock erosion. Consequently, within similar high competence systems, incision is probably progressive as long as sediment supply is sustained to abrade the bedrock. The landscape modelling implication is that abrasion in this system is supply‐limited and not limited by flow competence. In contrast, a transport‐limited system is likely to evolve to exhibit an alluvial bed. © 2018 John Wiley & Sons, Ltd.

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Non-universality of von Kármán's κ in fluvial streams

Cited by 73 publications

References 19 publications

The von Kármán constant for flows over rough mobile beds. Lessons learned from dimensional analysis and similarity

The von Kármán constant for flows over rough mobile beds. Lessons learned from dimensional analysis and similarity

Near-Bed Turbulence Characteristics at the Entrainment Threshold of Sediment Beds

Flow structure in large bedrock‐channels: The example of macroturbulent rapids, lower Mekong River, Southeast Asia

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