Granular-bed ripples and waves under an oscillating swirl flow: 

results from laboratory experiments

We perform laboratory experiments in a cylindrical tank mounted on top of an oscillating table. The axis of the table and the cylindrical tank are aligned with gravity. A granular bed is placed at the bottom of the tank, which is then filled with water. We are interested in the evolution of the patterns that form at the bed as a function of the frequency and the amplitude of a sinusoidal oscillation of the table. The bed forms are measured using a light attenuation technique. We observe the formation of radial ripples where the wavenumber and their radial extent depend on both the frequency and the amplitude of the oscillation. Furthermore, we study the displacement of the ripples when an additional sinusoidal oscillation with twice the original frequency is added. This is reminiscent of the movement of sand waves/ripples due to tidal asymmetries.