Wind energy has demonstrated its potential as a renewable energy source. Much research has been devoted to technologies that improve wind turbine efficiency, winglets being among them. Blade tip vortices increase induced drag and affect wind turbine lift generated. This affects power generated and efficiency of turbines. In aircraft, winglets have proven to reduce induced drag. However, winglets tend to increase wing bending moments, requiring structural reinforcement which could make winglets an expensive proposition. The primary objective of this study is to design a retrofit winglet for a baseline wind turbine, and determine economic feasibility. Unlike previous winglet designs, an innovative design philosophy has been adopted, attempting to balance aerodynamic forces normal to the winglet surface and generated centrifugal forces by careful configuration design and using lightweight material. Traditional methods to determine power output of a wind turbine, such as the blade element momentum theory, are insufficient to model a wind turbine with winglets. A vortex lattice method for rotor applications has been developed and implemented. Economic feasibility is a key issue in the wind industry today. Accordingly, a cost function that compares design, manufacture and labor costs against increment in power has been implemented. Using these tools, three winglets with varying construction techniques is investigated. The net result is a winglet configuration that, at minimum installation cost, provides improved performance and economic benefit.

Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering