A recently patented novel idea of an adjustable dual-rotor horizontal-axis wind turbine is investigated [1]. The idea behind this proposed design is to continue to extract more mechanical energy from the wind stream which has already passed through the front rotor by having a second identical rotor on the other side of the main shaft of the wind turbine. The complex flow in the dual-rotor is studied using computational fluid dynamics. The optimum performance of this unit is when the wake from each blade in the first rotor passes through the spacing between each two rear rotor blades while the undisturbed part of the wind stream is intercepted by the rear rotor blades. The strength and pattern of the wakes are determined for low and high wind speeds. The numerical study verified the feasibility of the proposed idea. The optimum orientation angle at which no interception of the front rotor wake by any of the rear rotor blades is found to be 60°.

The axial spacing between the front and rear rotors is also investigated. A small scale model was built and tested in a subsonic wind tunnel. The comparison showed that the dual-rotor wind turbine produced nearly 100% more power than the single-rotor wind turbine.

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