While vertical-axis wind turbines (VAWTs) have a simpler design than the horizontal-axis wind turbines, their development has been hindered... Show moreWhile vertical-axis wind turbines (VAWTs) have a simpler design than the horizontal-axis wind turbines, their development has been hindered due to their unsteady aerodynamics and complex flow field. In this thesis, a parameterized study is conducted to simulate a baseline VAWT using STAR-CCM+, a commercial finite volume code. A hybrid grid scheme, with structured prism layer mesh at the surface of the blades, is used to properly resolve the turbulent boundary layers on the blades. The flow was highly unsteady due to the rotating geometries. Thus, a sliding mesh technique is implemented at the interface of rotating and stationary zones. The dominant factors limiting the performance of the VAWTs are investigated for a range of moderate tip speed ratios, by visualizing the flow field and modeling the individual blade aerodynamics. The VAWT aerodynamics is shown to be dominated by the dynamic stall, at low tip speed ratios, and by the blade-wake interactions and the wake blockage effects, at high tip speed ratios. The concept of turbine coupling is used to improve the performance of the VAWTs by their internal aerodynamic interactions. Two counter-rotating turbines are placed in close proximity, and simulated over the same range of tip speed ratios as before, and for a set of different spacing between them. The effects of spacing and the tip speed ratio on their overall power output and their wake recovery characteristics are then investigated. A cluster of turbines with spacing equal to 1.50 turbine diameters and tip speed ratio of three is shown to have the quickest wake recovery and highest power enhancement, increasing the turbine average power coefficient by 22%. M.S. in Mechanical and Aerospace Engineering, July 2014 Show less
