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Revisiting slope influence in turbulent bedload transport: consequences for vertical flow structure and transport rate scaling

Maurin, Raphaël and Chauchat, Julien and Frey, Philippe Revisiting slope influence in turbulent bedload transport: consequences for vertical flow structure and transport rate scaling. (2018) Journal of Fluid Mechanics, 839. 135-156. ISSN 0022-1120

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Official URL: https://doi.org/10.1017/jfm.2017.903

Abstract

Gravity-driven turbulent bedload transport has been extensively studied over the past century in regard to its importance for Earth surface processes such as natural riverbed morphological evolution. In the present contribution, the influence of the longitudinal channel inclination angle on gravity-driven turbulent bedload transport is studied in an idealised framework considering steady and uniform flow conditions. From an analytical analysis based on the two-phase continuous equations, it is shown that : (i) the classical slope correction of the critical Shields number is based on an erroneous formulation of the buoyancy force, (ii) the influence of the slope is not restricted to the critical Shields number but affects the whole transport formula and (iii) pressure-driven and gravity-driven turbulent bedload transport are not equivalent from the slope influence standpoint. Analysing further the granular flow driving mechanisms, the longitudinal slope is shown to not only influence the fluid bed shear stress and the resistance of the granular bed, but also to affect the fluid flow inside the granular bed - responsible for the transition from bedload transport to debris flow. The relative influence of these coupled mechanisms allows us to understand the evolution of the vertical structure of the granular flow and to predict the transport rate scaling law as a function of a rescaled Shields number. The theoretical analysis is validated with coupled fluid-discrete element simulations of idealised gravity-driven turbulent bedload transport, performed over a wide range of Shields number values, density ratios and channel inclination angles. In particular, all the data are shown to collapse onto a master curve when considering the sediment transport rate as a function of the proposed rescaled Shields number.

Item Type:Article
HAL Id:hal-01937895
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Other partners > Université Grenoble Alpes - UGA (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UT3 (FRANCE)
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Funders:
Agence Nationale de la Recherche - ANR (FRANCE) - Université Grenoble Alpes - UGA (FRANCE) - Institut national des sciences de l'Univers - INSU (FRANCE) - Institut national des sciences de l'Univers - INSU (FRANCE)
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Deposited On:15 Mar 2019 09:14

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