Initial instabilities of a granular bed sheared by a turbulent liquid flow: length-scale determination

Franklin, Erick de Moraes

doi:10.1590/s1678-58782010000400008

Cited by 12 publications

(93 citation statements)

References 25 publications

(35 reference statements)

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“…The tests nominal flow rates were of 5, 5.5, 6, 6.5 and 7m 3 /h, corresponding to cross-section mean velocities in the range 0.19m/s ≤ U ≤ 0.29m/s and to Reynolds number Re = U 2H gap /ν in the range 16000 < Re < 27000, where H gap is the distance from the granular bed to the top wall. The flow rates' lower and upper bounds were fixed to, respectively, correspond to the bed-load threshold [1,3,18] and to avoid the formation of ripples on the granular bed within the time scale of the tests [19,20,21,22].…”

Section: Experimental Devicementioning

confidence: 99%

The feedback effect caused by bed load on a turbulent liquid flow

Franklin

Figueiredo

Rosa

2014

J Braz. Soc. Mech. Sci. Eng.

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Experiments on the effects due solely to a mobile granular layer on a liquid flow are presented (feedback effect). Nonintrusive measurements were performed in a closed conduit channel of rectangular cross section where grains were transported as bed load by a turbulent water flow. The water velocity profiles were measured over fixed and mobile granular beds of same granulometry by Particle Image Velocimetry. The spatial resolution of the measurements allowed the experimental quantification of the feedback effect. The present findings are of importance for predicting the bed-load transport rate and the pressure drop in activities related to the conveyance of grains.Comment: Accepted Manuscript for the Journal of the Brazilian Society of Mechanical Sciences and Engineering, v. 36, p. 725-736, 2014. The final publication is available at Springer via http://dx.doi.org/10.1007/s40430-013-0122-

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Section: Experimental Devicementioning

confidence: 99%

The feedback effect caused by bed load on a turbulent liquid flow

Franklin

Figueiredo

Rosa

2014

J Braz. Soc. Mech. Sci. Eng.

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“…The longitudinal evolution of the perturbed flow is of importance to understand the formation of sand ripples. For the growth of ripples, the fluid flow must be an unstable mechanism, which means that the surface shear stress caused by the fluid must reach its maximum upstream of the bedform crests [1,2,3,11]. Therefore, in the following we focus our attention on the region upstream of the ripple crest.…”

Section: Perturbed Flowmentioning

confidence: 99%

“…The new velocity and stress distributions are of importance for many engineering applications. For instance, when in the presence of sediment transport the stress distribution along the hill is an essential parameter to understand the bed instabilities [1,2,3].…”

Section: Introductionmentioning

confidence: 99%

“…In the case of loose granular beds, the longitudinal evolution of the shear stress determines if the fluid flow is an unstable mechanism, so that Eqs. 2 to 4 are of importance for stability analyses of sand ripples and dunes [1,2,3,11]. Formally, asymptotic methods are applied to hills with aspect ratios of h max (4L) −1 < 0.05 [5,6,12], where the total length of the bedform is approximately 4L and h max corresponds to its maximum height.…”

Section: Introductionmentioning

confidence: 99%

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The perturbation of a turbulent boundary layer by a two-dimensional hill

Franklin¹,

Ayek²

2013

J Braz. Soc. Mech. Sci. Eng.

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Turbulent boundary layers over flat walls in the presence of a hill are frequently found in nature and industry. Some examples are the air flows over hills and desert dunes, but also water flows over aquatic dunes inside closed conduits. The perturbation of a two-dimensional boundary layer by a hill introduces new scales in the problem, changing the way in which velocities and stresses are distributed along the flow. When in the presence of sediment transport, the stress distribution along the hill is strongly related to bed instabilities. This paper presents an experimental study on the perturbation of a fully-developed turbulent boundary layer by a two-dimensional hill. Water flows were imposed over a hill fixed on the bottom wall of a closed conduit and the flow field was measured by Particle Image Velocimetry. From the flow measurements, mean and fluctuation fields were computed. The general behaviors of velocities and stresses are compared to published asymptotic analyses and the surface shear stress is analyzed in terms of instabilities of a granular bed.Comment: This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/. Accepted Manuscript for the Journal of the Brazilian Society of Mechanical Sciences and Engineering, v. 35, p. 337-346, 201

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“…Franklin [5] presented a nonlinear stability analysis within the same scope as one of his previous papers [4]. This nonlinear analysis, based on the weakly nonlinear approach [18], showed that the initial bed instabilities saturate, because of which the wavelengths of ripples can be predicted by linear analyses even if ripples observed in nature are in a nonlinear regime.…”

Section: Introductionmentioning

confidence: 99%

Formation of sand ripples under a turbulent liquid flow

Franklin

2015

Applied Mathematical Modelling

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Sand ripples are commonly observed in both nature and industry. For example, they are found on riverbeds and in oil pipelines that transport sand. In both natural and industrial cases, ripples increase friction between the bed and fluid and are related to flooding, high pressure drops, and transients. Ripples appear when sediments are entrained as bed load (a mobile granular layer) and are usually considered to be the result of initial bedforms that eventually saturate. Given the small aspect ratio of the initial bedforms, linear analyses can be used to understand the formation of ripples. This paper presents a linear stability analysis of a granular bed under a turbulent flow of a liquid. This analysis takes into consideration all the main mechanisms and parameters involved in the turbulent liquid case, including some important parameters that have not yet been considered together such as the bed compactness and the bed-load threshold shear stress. The results of this analysis are compared with published experimental results and they show good agreement.Comment: This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0

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Initial instabilities of a granular bed sheared by a turbulent liquid flow: length-scale determination

Cited by 12 publications

References 25 publications

The feedback effect caused by bed load on a turbulent liquid flow

The feedback effect caused by bed load on a turbulent liquid flow

The perturbation of a turbulent boundary layer by a two-dimensional hill

Formation of sand ripples under a turbulent liquid flow

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