Aerodynamic Design and Control of Vertical Axis Wind Turbines

The need to combat climate change and find alternate solutions to fossil fuel is at an all time high. Researchers continue to drive the advancement of wind turbine technology since it is a viable alternate solution towards a sustainable future. With the advancement of wind turbine technology over the last 20 years, horizontal axis wind turbines (HAWTs) particularly have received more attention. But there is an alternate turbine configuration called vertical axis wind turbine (VAWTs). Some of the advantages of VAWTs over HAWTs are namely, it’s independent of wind direction, low sound emissions, easy access to turbine components like generator and gearbox (due to placement at tower base) and lower topside center of gravity compared to HAWTs. This thesis focuses on the aerodynamic design study and development of control strategy of conventional troposkein shaped Darrieus vertical axis wind turbines (VAWTs) using CACTUS (Code for Axial and Crossflow TUrbine Simulation), which is a 3D numerical vortex based lifting line aerodynamic model. The first half of the thesis focuses on the detailed aerodynamic design study of VAWTs and how the selection of various design variables affect this design process. This study systematically analyzes the effect of different design variables including the number of blades (N), aspect ratio (AR) and blade tapering in a comprehensive loads analysis of both the parked and operating aerodynamic loads including turbine power performance analysis. The second half of the thesis focuses on the development of a novel method to control rotor dynamics named intracycle RPM control strategy, for VAWTs. VAWTs perform sub-optimally in regions 2 and 3 due to the absence of a pitch mechanism and low starting torque, which significantly affects their annual energy production. But introducing a pitching mechanism in VAWTs also takes away one of its biggest advantages over its competitors, which is mechanical simplicity. An alternate control strategy named intracycle RPM control or intracycle angular velocity control is presented, where the rotational speed of the turbine is allowed to vary with the azimuthal location of blades, which is able to alter the rotor inflow conditions to maximize power output while having constraining the loads. With the help of an optimizer named GPOPSII, which optimizes the rotational speed over a single revolution at a particular wind speed, coupled with CACTUS, which measures the performance of the rotor, it is shown that the aerodynamic AEP can be increased while restraining loads at prescribed limits.