An experimental study of bathymetry influence on turbulence at a tidal stream site

International audienceThis study aims at completing the lack of knowledge on turbulence characteristics in high flow velocity areas like those suitable for marine energy application. We present in this paper the methodology used to recreate the turbulent phenomenon existing in the Raz Blanchard by representing significant sea-bed elements in a circulating tank. The first set of experiment was achieved for the flow measurement results obtained around a wall-mounted cube at Re = 2.5 × 10 5 and F r = 0.23, in representative in-situ conditions. These measurements have been done for different kinds of flow from laminar to highly turbulent (turbulence intensity rate from 3 to 15%) in both horizontal and vertical planes, using LDV and PIV measurements. The study shows similar results for the low turbulence intensity cases in terms of flow topology (stagnation point, recirculation length and energetic considerations). It is also shown that the wall-mounted cube does not create the structures observed in-situ. Indeed, the structures of interest here are very persistent macroturbulences that may be generated at the sea floor and erupt at the free surface. The possibility that these structures could be Kolk vortices is considered. In order to recreate such phenomena, the idea of placing an inclined floor downstream of the cube is investigated. The results show that turbulent structures are significantly impulsed by a 6.5 • inclined floor and rise up to 13% higher in the water column. The question of the aspect ratio of the obstacle is also investigated. Furthermore, numerical simulations on dune with similar incoming flow conditions show encouraging results and indicate the path for further experimental testing