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Subaqueous barchan dunes in turbulent shear flow. Part 1. Dune motion

Published online by Cambridge University Press:  30 March 2011

E. M. FRANKLIN  and
F. CHARRU
E. M. FRANKLIN
Affiliation:
Institut de Mécanique des Fluides de Toulouse – CNRS – Université de Toulouse – Allée C. Soula, 31400 Toulouse, France
F. CHARRU*
Affiliation:
Institut de Mécanique des Fluides de Toulouse – CNRS – Université de Toulouse – Allée C. Soula, 31400 Toulouse, France
*
†Email address for correspondence: Francois.Charru@imft.fr
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Abstract

Experiments are reported on the formation and migration of isolated dunes in a turbulent channel flow. These dunes have a very robust crescentic shape with horns pointing downstream, very similar to that of the barchan dunes observed in deserts at a much larger scale. Their main geometrical and dynamical properties are studied in detail, for four types of grains: the conditions for their formation, their morphology, the threshold shear stress for their motion, their velocity, erosion rate, minimum size and the longitudinal stripes of grains hollowed by fluid streaks in the boundary layer. In particular, the law for the dune velocity is found to involve two dimensionless parameters, the Shields number and the sedimentation Reynolds number, in contrast with predictions based on classical laws for particle transport. As the dune migrates, its size slowly decreases because of a small leakage of particles at the horn tips, and the erosion law is given. A minimum size is evidenced, which is shown to increase with the friction velocity and scale with a settling length.

JFM classification

Granular media: Granular media Multiphase and Particle-laden Flows: Particle/fluid flow Geophysical and Geological Flows: Sediment transport
Type
Papers
Information
Journal of Fluid Mechanics , Volume 675 , 25 May 2011 , pp. 199 - 222
Copyright
Copyright © Cambridge University Press 2011

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