Nonlinear instabilities on a granular bed sheared by a turbulent liquid flow

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FONTE

Journal of the Brazilian Society of Mechanical Sciences and Engineering

DATA DE PUBLICAÇÃO

2011-09

RESUMO

The granular media is of great importance in our quotidian, and their transport by a fluid flow is frequently found in nature and in industry. When the shear stresses exerted by the fluid flow on a granular bed are bounded to some limits, a mobile granular layer known as bed-load takes place in which the grains stay in contact with the fixed part of the granular bed. Under these conditions, a flat granular bed may be unstable, generating ripples and dunes. In a recent article (Franklin, 2010), the mechanisms of this instability were explained and a linear stability analysis was presented, in which a scaling between the fluid flow conditions and the typical length of the initial bed-forms was proposed. The present paper proposes a nonlinear stability analysis (weakly nonlinear approach) applicable to sheared granular beds, shedding light on the evolution of the bed-forms after their initial phase. The scope of the nonlinear analysis is the same as that of Franklin (2010): granular beds under turbulent liquid flows and in the presence of bed-load. It is shown here that, in this case, the initial instabilities saturate (supercritical bifurcation). Also, a discussion is made on some published experimental data.

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