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Instabilité d'un lit granulaire cisaillé par un écoulement fluide

Abstract : This work deals with experimental, theoretical and numerical investigations on
the instability of a granular bed when sheared by a steady fluid flow.

We built an open flume set-up to study the growth and dynamics of
ripples on the surface of a sand bed. We determined the
wavelength at the onset of instability as a function of flowrate and
grain size, and the evolution of the mean amplitude and wavelength
of the ripples (through a coarsening process). We observed a shape
transition from 2D ripples, that are perpendicular to the flow, to more complex
3D patterns.

Besides, we carried out a theoretical stability analysis, in the
case of a laminar fluid flow. This calculation correctly captures the
initial wavelength of the structure if the effect of grain inertia is taken
into account. We also predicted the existence of 3D structures by
performing a nonlinear analysis.

Finally, we studied the nonlinear dynamics of ripples. 2D numerical simulations,
based on the previous theoretical computation, gave a qualitative
long-time evolution similar to our experiments on ripples. We used a
simplified nonlinear model to show that 3D structures may be a necessary
transient state in the coarsening process of ripples.
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Contributor : Vincent Langlois <>
Submitted on : Tuesday, January 24, 2006 - 6:04:10 PM
Last modification on : Tuesday, January 12, 2021 - 4:40:13 PM
Long-term archiving on: : Saturday, April 3, 2010 - 9:43:20 PM


  • HAL Id : tel-00011456, version 1


Vincent Langlois. Instabilité d'un lit granulaire cisaillé par un écoulement fluide. Dynamique des Fluides [physics.flu-dyn]. Université Rennes 1, 2005. Français. ⟨tel-00011456⟩



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