EFFECTS OF UNSTEADY AERODYNAMICS ON VERTICAL-AXIS WIND TURBINE PERFORMANCE Kozak, Peter 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 2014 Rempfer, Dietmar 2014 2014-05 Thesis application/pdf islandora:7288 http://hdl.handle.net/10560/3277 MMAE / Mechanical, Materials, and Aerospace Engineering Illinois Institute of Technology en In Copyright http://rightsstatements.org/page/InC/1.0/ Restricted Access