Experiments

Our experimental set-up in Rennes is a 3 meter long rectangular flume, in which a bed of glass beads is eroded by a water flow coming from a heightened water tank. The flume is covered by a lid so that the flow does not present any free surface. Starting from a plane sand surface, we obtain 3D ripples after a few minutes. The elevation profile of the bed is measured by a laser telemeter mounted on a motorized rail. The evolution of localized structures can also be characterized by the deformation of a laser sheet.

We perform P.I.V. (Particle Imaging Velocimetry) measurements to characterize the water flow properties and to relate them to the bedforms. This method consists in seeding the flow with 10 µm shiny particles, and lightening them with a powerful laser sheet. The velocity field is then calculated from the correlation of two successive images taken by a fast camera.