Influence of duct geometry on Achard turbine efficiency

In order to increase the efficiency of the Achard turbine, we propose a new duct geometry yielding to a shrouded Achard turbine: a turbine running within a channeling device with S-shaped vertical walls, in a free flow domain. Several Achard turbines, superposed, form towers. For such towers, the flow is almost unchanged in horizontal planes along the vertical axis, allowing thus 2D numerical modeling in a cross-section of the tower. The 2D modeling of the transient flow inside the shrouded Achard turbine with straight blades was performed with COMSOL Multiphysics. The studied case focuses on a row of two towers, placed across the water flow direction. In order to depict the influence of the duct geometry on turbine's efficiency (power coefficient), our results were compared with other results obtained for shrouded Achard turbines running within a different type of duct: a symmetric two-foiled channeling device. Both duct geometries proved to increase the turbine efficiency with respect to the case of an isolated Achard turbine.