Gravel-Bed Hydrodynamics: Double-Averaging Approach

Dey, Subhasish; Das, Ratul

doi:10.1061/(asce)hy.1943-7900.0000554

Cited by 90 publications

(88 citation statements)

References 28 publications

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“…Thus, differences in velocity sampling as well as relative submergence could contribute to the variation in values between all the studies in Table . However it is unclear how differences in bed topography influence the variation for three reasons: (i) in the present study, when differences in spatial flow variance and form‐induced stress were analyzed against different roughness properties (e.g., standard deviation in bed elevation, geometric roughness height, and grain‐size percentiles) no systematic change was found; (ii) Dey and Das [], in comparing their form‐induced stress values to those measured by Mignot et al . [] and Sarkar and Dey [], showed that form‐induced stress increases with roughness size.…”

Section: Discussionmentioning

confidence: 99%

Influence of relative submergence on spatial variance and form-induced stress of gravel-bed flows

et al. 2013

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[1] Spatial flow variance has a strong control on sediment transport, sediment-water interface exchange mechanisms, and the distribution and behavior of aquatic organisms in rivers. Thus, being able to quantify spatial flow variance, and how it varies with different water levels, is important for understanding how fluvial processes change during periods of time varying flow. In this paper, laboratory flume measurements of near-bed flow velocity were used to quantify spatial flow variance and form-induced stress, and their variation with flow submergence, within and above the surface of porous, gravel beds with differing grain roughness. The analysis revealed spatial flow variance was usually four or five times higher within the roughness layer than above. A rise in relative submergence resulted typically in a decrease in spatial variance-relative to bed shear velocity-in streamwise form-induced intensity, streamwise turbulence intensity, and form-induced momentum flux, both within and above the roughness layer. Flow submergence had no consistent influence on spatial variance in the vertical flow direction and in Reynolds stress. Form-induced stress was significant within the roughness layer, more so at shallow depths. The greater significance was driven primarily by higher spatial flow variance in time-averaged streamwise velocity at these depths. The implication is the relative role of momentum transfer mechanisms within the roughness layer, and thus, sediment-water interface exchange processes in rivers will change during periods of time varying flows.

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Section: Discussionmentioning

confidence: 99%

Influence of relative submergence on spatial variance and form-induced stress of gravel-bed flows

et al. 2013

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“…[], they somewhat differ from findings of Manes et al . [] and Dey and Das [] who revealed fairly sharp peaks of

{true〈 {\overset{u}{true}}_{i}^{2} true〉}^{1 / 2} / u_{*}

at the roughness crests. The form‐induced intensity

{true〈 {\overset{u}{true}}_{w}^{2} true〉}^{1 / 2} / u_{*}

assumes values at the gravel crests ranging between 0.2 and 0.3, similar to those obtained by Manes et al .…”

Section: Flow Structurementioning

confidence: 91%

The structure of gravel‐bed flow with intermediate submergence: A laboratory study

Mohajeri

Grizzi

Righetti

et al. 2015

Water Resources Research

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The paper reports an experimental study of the flow structure over an immobile gravel bed in open channel at intermediate submergence, with particular focus on the near‐bed region. The experiments consisted of velocity measurements using three‐component (stereoscopic) Particle Image Velocimetry (PIV) in near‐bed horizontal plane and two‐component PIV in three vertical planes that covered three distinctly different hydraulic scenarios where the ratio of flow depth to roughness height (i.e., relative submergence) changes from 7.5 to 10.8. Detailed velocity measurements were supplemented with fine‐scale bed elevation data obtained with a laser scanner. The data revealed longitudinal low‐momentum and high‐momentum “strips” in the time‐averaged velocity field, likely induced by secondary currents. This depth‐scale pattern was superimposed with particle‐scale patches of flow heterogeneity induced by gravel particle protrusions. A similar picture emerged when considering second‐order velocity moments. The interaction between the flow field and gravel‐bed protrusions is assessed using cross correlations of velocity components and bed elevations in a horizontal plane just above gravel particle crests. The cross correlations suggest that upward and downward fluid motions are mainly associated with upstream‐facing and lee sides of particles, respectively. Results also show that the relative submergence affects the turbulence intensity profiles for vertical velocity over the whole flow depth, while only a weak effect, limited to the near‐bed region, is noticed for streamwise velocity component. The approximation of mean velocity profiles with a logarithmic formula reveals that log‐profile parameters depend on relative submergence, highlighting inapplicability of a conventional “universal” logarithmic law for gravel‐bed flows with intermediate submergence.

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“…The raw Vectrino data were despiked by the acceleration threshold method (Goring and Nikora, 2002), which was capable in identifying and substituting spikes. The threshold values were chosen in the ranges between 1-1.5 by trial and error (Dey and Das, 2012).…”

Section: Experimental Facilitymentioning

confidence: 99%

Measurement of turbulent flow in a narrow open channel

Sarkar

2016

Journal of Hydrology and Hydromechanics

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Abstract:The paper presents the experimental results of turbulent flow over hydraulically smooth and rough beds. Experiments were conducted in a rectangular flume under the aspect ratio b/h = 2 (b = width of the channel 0.5 m, and h = flow depth 0.25 m) for both the bed conditions. For the hydraulically rough bed, the roughness was created by using 3/8″ commercially available angular crushed stone chips; whereas sand of a median diameter d 50 = 1.9 mm was used as the bed material for hydraulically smooth bed. The three-dimensional velocity components were captured by using a Vectrino (an acoustic Doppler velocimeter). The study focuses mainly on the turbulent characteristics within the dip that were observed towards the sidewall (corner) of the channel where the maximum velocity occurs below the free-surface. It was also observed that the nondimensional Reynolds shear stress changes its sign from positive to negative within the dip. The quadrant plots for the turbulent bursting shows that the signs of all the bursting events change within the dip. Below the dip, the probability of the occurrence of sweeps and ejections are more than that of inward and outward interactions. On the other hand, within the dip, the probability of the occurrence of the outward and inward interactions is more than that of sweeps and ejections.

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Gravel-Bed Hydrodynamics: Double-Averaging Approach

Cited by 90 publications

References 28 publications

Influence of relative submergence on spatial variance and form-induced stress of gravel-bed flows

Influence of relative submergence on spatial variance and form-induced stress of gravel-bed flows

The structure of gravel‐bed flow with intermediate submergence: A laboratory study

Measurement of turbulent flow in a narrow open channel

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