<p>Many studies have been performed on ducted wind turbines including our recent study that determined an optimal duct length when optimizing for maximum power per total device cross-sectional area i.e. including the duct area. However, it is not clear whether there is an upper limit to the power that can be obtained per rotor area with increasing duct length.&nbsp;&nbsp;To determine this, analytical modeling was used along with Reynolds-averaged Navier-Stokes CFD simulations with&nbsp;k-ω SST&nbsp;turbulence model to simulate a ducted wind turbine where an actuator disc was used to model the rotor. The simulations were used to optimize the design of the ducted wind turbine. A pattern search method was applied to find the optimal design. The design variables included the chord length of the duct, angle of attack of the cross-section of the duct, the thrust coefficient of the rotor, the normal rotor gap between the tip of the rotor and the duct, and the axial location of the rotor inside the rotor. The Eppler E423 airfoil was used for the cross-section of the duct in the simulations. The objective function for optimization was the power coefficient defined based on the rotor area of the DWT. The results indicate that at least for duct lengths that seem practical (with the duct length smaller than rotor diameter), the optimal power output basically linearly increases with the duct length of the duct. The results also showed that, although the objective function is sensitive to the thrust coefficient of the rotor, the optimal thrust coefficient is close to 0.9 independent of the duct length. The ratio of the optimal normal rotor gap to the boundary layer thickness at the rotor was insensitivte to duct size and remained close to one. The optimal design tends to be close to flow separation with the rotor placed near the duct throat independent of the duct length.&nbsp;</p>

Optimal Aerodynamic Design of Ducted Wind Turbines for Maximum Power Output

Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2021/volume/85284

ASME 2021 Fluids Engineering Division Summer Meeting (FEDSM2021)

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