Parametric Design of a Dual-Component Ducted Turbine

Abstract

Wind is a readily available source of renewable energy, but difficult to use efficiently and economically because of its intermittent nature. While ducted wind turbines yield more power than a turbine in free air, they often experience separation and stalling on the diffuser as wind speed varies, substantially decreasing their effective-ness at speeds that vary significantly from the design point. This thesis explores a dual-component duct design, in which a small secondary ring with an airfoil cross-section is added near the trailing edge of the primary duct in order to create an airflow path that re-energizes the boundary layer on the diffuser and minimizes separation, thereby increasing flow through the duct. The secondary airfoil was intended to be adjustable in order to increase the range of efficient operating conditions relative to traditional single-point designs. The duct was designed by carrying out simulations using ANSYS Fluent while varying placement, rotation, and camber to find the most effective geometry. The added secondary ring yielded 14% higher axial velocity at the duct throat than the single ring alone, 2.4 times higher than the freestream velocity. Upon implementing a simple turbine model, this design also increased power output to an average of 2.4 times more than the maximum power theoretically available from a turbine operating at the Betz limit in free air. This proved to be a robust system, yielding the same proportional power increase for freestream speeds ranging from 6.18 m/s to 16.5 m/s. With or without a turbine, the same location of the secondary component yielded the highest performance regardless of changes in freestream velocity or turbine thrust, indicating that it was not necessary that the system be adjustable. Although this design is more complex and therefore more expensive than conventional ducted wind turbines, the power advantages and wide range of high-efficiency operating conditions are likely to offset the cost, especially after further optimization of the airfoils.