Accepted Manuscripts

Ravon Venters, Brian Helenbrook and Kenneth D. Visser
J. Sol. Energy Eng   doi: 10.1115/1.4037741
Ducted wind turbines (DWT) present a viable alternative to open-rotor wind turbines, by increasing the momentum through the turbine, thereby improving the power output. This study presents a numerical optimization of the duct configuration to maximize power output. The cross-section of the duct is an Eppler 423 airfoil, which is a cambered airfoil with a high lift coefficient (C_L). The rotor was modeled as an actuator disc and the Reynolds-averaged-Navier-Stokes (RANS) k-epsilon model was used to simulate the flow. To verify the accuracy of this formulation, 2D numerical simulations of the airfoil were compared to experimental data. The 2D airfoil results followed the same trend as experimental data predicting the angle of attack of maximum lift to within a few degrees, but over predicted the coefficient of lift by 15%. Using the k-epsilon model, an axisymmetric DWT geometry was optimized. It was determined that that the optimal coefficient of thrust is similar to an open rotor. The optimal angle of attack of the duct was much larger than the separation angle of attack of the airfoil in a freestream. For the same rotor area, the power output of the largest DWT was 66% greater than an open rotor because of the flow induced by the duct. For the same total cross sectional area of the entire device, the DWT also outperformed an open rotor, exceeding Betz's limit by a small margin.
TOPICS: Optimization, Wind turbines, Rotors, Airfoils, Discrete wavelet transforms, Ducts, Flow (Dynamics), Separation (Technology), Computer simulation, Thrust, Actuators, Turbines, Disks, Geometry, Reynolds-averaged Navier–Stokes equations, Momentum

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