  The transport of solid particles by a fluid flow is frequently found in
nature and industry. Some examples are the transport of sand in rivers and
hydrocarbon pipelines. When the shear stresses exerted by a fluid flow on a
granular bed remain moderate, some grains are set in motion without fluidizing
the bed; the moving grains form a layer, known as bed load, that moves while
maintaining contact with the fixed part of the bed. Under bed load conditions,
the granular bed may become unstable, generating ripples and dunes. Sand
ripples are commonly observed in closed conduits and pipes such as in petroleum
pipelines, sewer systems, and dredging lines. Although of importance for many
scientific domains and industrial applications, the formation of ripples in
closed conduits is not well understood, and the problem is still open. This
paper presents an experimental study on the formation and migration of sand
ripples under a turbulent closed-conduit flow and bed-load conditions. In our
experiments, fully-developed turbulent water flows were imposed over a granular
bed of known granulometry in a transparent channel, and bed load took place.
For different water flow rates and grain diameters, the growth and migration of
bedforms were filmed by a high-definition camera, and a numerical code was
developed to determine the wavelength and celerity of the bedforms from the
acquired images. The obtained results are compared with published stability
analyses.
