Periodic saltation under extreme tidal currents: an experimental study
Résumé
In extreme tidal environment and specifically in the Alderney race (English Channel, France), the ambition to install hydrokinetic turbines requires knowledge on the pebbles concentration in the water column. Some evidences of the
presence of such coarse sediments at one meter above the bed have been found. An experimental study is realized
in a free surface flume for high Stokes number. With fast camera the trajectories of hundreds of spherical particles are
analyzed. This study focuses on the characterization of the critical Shields number to intermittent and saltation regime
and on the coefficient of restitution between the impact and the rebound velocity . The critical Shields number
is identified experimentally at 0.2. The restitution coefficient shows little dependence on the impact angle. Finally, the
experimental maximum height reached by the spherical particles proves that lift and inertia forces are not negligible.