CFD Investigation of the Open Center on the Performance of a Tidal Current Turbine

In the present paper, a revision of the layout of an innovative open center self-balancing tidal turbine is presented. Initially, the design was characterized by a central deflector, responsible for the machine equilibrium, hosted in the central part of the machine; the presence of this device, however, affected the size of the opening. Moreover, the turbine was conceived as connected to a steel rope subject to tensile stress. These peculiarities brought some critical issues due to the excessive length of the rope and to the size of the deflector, which constrained the diameters ratio. The new design involves the possibility of reducing the anchoring line length by substituting the rope with a series of tubular elements connected by alternate heavy and light nodes. The heavy nodes can gather the anchoring line when the tides stops acting. Moreover, the light nodes are floating deflectors, which develop the same action of the central deflector, whose size, in this configuration, does not affect the equilibrium. In the new machine configuration, the main deflector is located out of the center so that it can counterbalance the torque exerted by the rotor during its rotation. Finally, by means of CFD simulations, some criteria for assessing the best diameter ratio are defined.