Aerodynamic interaction of diffuser augmented wind turbines in multi-rotor systems

The most common wind turbine is the single-rotor, horizontal axis wind turbine. In order to reduce the cost of energy, upscaling of single-rotor wind turbines has been a major trend. Recent studies however show that for a given technology, the cost usually rises when upscaling, notably due to increased masses. To reach capacities beyond 10 MW, multi-rotor systems (MRS) have promising advantages over single-rotor systems (SRS). On the other hand, diffuser augmented wind turbines (DAWTs) can significantly increase the performance of the turbine. In this research, brimmed DAWTs are introduced in a MRS. In wind tunnel experiments, the aerodynamics of two and three DAWTs, spaced in close vicinity in the same plane normal to a uniform flow, have been analyzed. Power increases of up to 5% and 9% for the two and three rotor configurations are respectively achieved in comparison to a single-rotor turbine. Hot-wire techniques used to measure the flow speed near the gap between the DAWTs in a MRS have shown an acceleration of the flow. Phenomena of bluff body flows are reviewed to analyze the physical dynamics of the flows in the MRS on the basis of the flow dynamics observed in a SRS.