Fluvial Processes

Silva, Ana Maria Ferreira da; Yalin, M. Selim

doi:10.4324/9781315206189

Cited by 24 publications

(21 citation statements)

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“…The value of (τ0)cr was determined from Eq. (1.34) in da Silva and Yalin [27], which for D = 1 mm yields (τ0)cr =0.677 Pa. The resulting values of qsb along the pertinent dune are plotted in Fig.…”

Section: Bed Shear Stress and Bed-load Ratementioning

confidence: 97%

“…Here qsb is specific volumetric bed-load rate, ub is flow velocity at the bed, and β is a coefficient which for the present flow conditions can be identified with 0.5. Following da Silva and Yalin [27], ub was calculated as ub = (uks+uε)/2 where uks and uε are the values of u at z = ks and z = ε, respectively, with ε being the height of the bed-load layer. This was calculated from the relation 0.7 0.5…”

Section: Bed Shear Stress and Bed-load Ratementioning

confidence: 99%

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Quantification of bed-load transport over dunes

2018

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There is disagreement in the literature as to whether a shear stress-based approach can be used to accurately predict sediment transport over dunes. This study aims to address this disagreement. To this end, use is made of an experiment involving the study of naturally formed, fully developed dunes produced in a laboratory flume. The bed shear stress is estimated through a combination of velocity, Reynolds stress measurements, and results of a CFD RANS rough wall model. The validity of using Bagnold’s equation to predict the bed-load rate is subsequently analyzed. In contrast to what has been previously suggested by some authors, it is found from the present experiment that the bed-load rate correlates well with the bed shear stress, and that Bagnold’s equation yields realistic values of the bed-load rate over the stoss side of the dune downstream of the reattachment point. This work also highlights the difficulties in reliably estimating the bed shear stress in complex flows. Such difficulties are overcome in this paper through a combination of flow velocity measurements and modeled results.

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Section: Bed Shear Stress and Bed-load Ratementioning

confidence: 97%

Section: Bed Shear Stress and Bed-load Ratementioning

confidence: 99%

Quantification of bed-load transport over dunes

2018

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“…(where u and w are the temporal velocity fluctuations in the streamwise and vertical directions, respectively, and z c is the maximum gravel crest elevation). Hence, the Reynolds number of the sediments Re * was calculated as u * ε/υ, where ε is the equivalent sand roughness height ≈ 2d 50 [33].…”

Section: Experimental Set-up and Proceduresmentioning

confidence: 99%

Turbulent Flow Field around Horizontal Cylinders with Scour Hole

Penna

Coscarella

Gaudio

2020

Water

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This study presents the results of an experimental investigation on the flow-structure interactions at scoured horizontal cylinders, varying the gap between the cylinder and the bed surface. A 2D Particle Image Velocimetry (PIV) system was used to measure the flow field in a vertical plane at the end of the scouring process. Instantaneous and ensemble-averaged velocity and vorticity fields, viscous and Reynolds stresses, and ensemble-averaged turbulence indicators were calculated. Longitudinal bed profiles were measured at the equilibrium. The results revealed that suspended and laid on cylinders behave differently from half-buried cylinders if subjected to the same hydraulic conditions. In the latter case, vortex shedding downstream of the cylinder is suppressed by the presence of the bed surface that causes an asymmetry in the development of the vortices. This implies that strong turbulent mixing processes occur downstream of the uncovered cylinders, whereas in the case of half-buried cylinders they are confined within the scour hole.

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“…These methods were developed under different conditions and some of them consider more variables than the others. Furthermore, it should be noted that most of the methods do not consider enough geometric variables and even the flow conditions are often neglected as parameters of the equations [6].…”

Section: Introductionmentioning

confidence: 99%

A new method to predict average flow velocity and conveyance capacity of meandering streams

Gamboa-Monge¹,

Ferreira-Da-Silva²,

Segura-Serrano³

et al. 2020

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This paper aims to be a contribution to the evaluation of the resistance factor of the alluvial meandering streams of natural origin. The well-known “divided resistance” approach, commonly adopted nowadays for straight streams with a bed covered by ripples and dunes is extended to include an additional term that considers the resistance due to the meandering of the stream. For the present analysis, 40 laboratory experiments and 285 field observations are evaluated, where it is found that the contribution of the meandering of the stream to its overall resistance may vary from negligible to very substantial, which depends on the stream geometric and flow conditions. In addition, it is determined that the most influential components for the resistance factor in meandering conditions depend on the relation between channel-averaged flow depth (hav) and the average grain size of the bed material (D50), the deflection angle of a meandering flow at the crossover Oi (θ0), and also the relation between flow width (B) and the channel-averaged flow depth (hav); these relations are used to develop a mathematical expression capable to predict the resistance to flow due to the meandering of the stream. It is shown that the equation introduced in this paper leads to considerably improved predictions of average flow velocity and conveyance capacity of meandering streams, which is of significance for an improved management of inland waterways.

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Fluvial Processes

Cited by 24 publications

References 0 publications

Quantification of bed-load transport over dunes

Quantification of bed-load transport over dunes

Turbulent Flow Field around Horizontal Cylinders with Scour Hole

A new method to predict average flow velocity and conveyance capacity of meandering streams

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