Experimental determination of wrinkles formation on a granular bed

Abstract

The transport of granular matter by a fluid flow is frequently found in nature and in industry. It is present, for example, in the erosion of river banks, in the displacement of desert dunes and in hydrocarbon pipelines conveying sand. When the shear stresses exerted by the fluid flow on a granular bed are bounded to some limits, some grains are entrained, but without fluidizing the bed: 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, an initially flat granular bed may be unstable, generating ripples and dunes. In the case of rivers, these forms create a supplementary friction between the bed and the water, affecting the water depth and being related to flood and navigation problems. In industry, examples are mostly related to closed-conduit flows conveying grains, such as hydrocarbon pipelines conveying sand. In such cases, bedforms generate supplementary pressure loss, but also pressure and flow rate transients. Although of importance for many scientific domains, the bed load and the instabilities of a granular bed are not well understood. This IC (undergraduate project) proposes an experimental study concerning the formation of ripples and dunes, contributing to a better knowledge of the subject. The experiments will be performed in transparent ducts, where bed load will occur. The bed-load flow rate and the formation and the migration of ripples and dunes will be measured by optical techniques.