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.