Hydrodynamic Interactions Between Three Closely-spaced Vertical Axis Tidal Turbines

A CFD analysis of the hydrodynamic interactions between three vertical axis tidal turbines set in close proximity is performed for two layout: side-by-side and triangular. The following key mechanisms are found to determine a power increasing with respect to isolated turbines: (1) turbine blockage that entails flow acceleration outside of the turbines and inside the aisles between adjacent turbines; (2) more favorable direction of the flow approaching the blade during upwind; (3) wake contraction, that increases torque generation during downwind. Blockage is responsible for a moderate performance increasing exhibited by the triangular layout. Change in the direction of the flow approaching the blades and wake contraction only occur for side-by-side layout, and lead to a significant increasing of efficiency. The side-by-side layout allows a wider range of flow directions that make possible a power gain, and thus it could be adoptable for tidal currents characterized by an incomplete inversion of the current direction. The behaviors of the two arrangements are compared for a real case located in the Strait of Messina.