EFFECTS OF UNSTEADY AERODYNAMICS ON VERTICAL-AXIS WIND TURBINE PERFORMANCE

Vertical-axis wind turbines (VAWTs) o er an inherently simpler design than horizontal-axis machines, while their lower blade speed mitigates safety and noise concerns. As a result, VAWTs can be used to open up more populated areas for large-scale wind energy development. While vertical-axis turbines do o er signi cant operational advantages, development has been hampered by the di culty of mod- eling the aerodynamics involved, along with their rotating geometry. This thesis presents results from a simulation of a baseline VAWT computed using Star-CCM+, a commercial nite volume (FVM) code. Overset grid techniques are used to model the VAWT's complex and moving geometry. VAWT aerodynamics are shown to be dominated at low tip-speed ratios by dynamic stall phenomena and at high tip-speed ratios by wake-blade interactions, using ow visualization and blade angle of attack. An iterative procedure to optimize the VAWT's geometry is developed using blade pitch to mitigate the adverse e ects of dynamic stall for a tip-speed ratio of 2.0 case. Relying on both a constant blade pitch o set as well as a variable blade pitch as a function of azimuthal angle, power output was shown to be increased by 17% and 38%, respectively, compared to the baseline case. Emphasis is placed on the modeling techniques used in the FVM simulation and the optimization process.M.S. in Mechanical and Aerospace Engineering, May 201