Aerodynamic response and three-dimensional flow characteristics of floating vertical axis wind turbines with blade pitch control

The offshore floating vertical axis wind turbines (VAWTs) show lower aerodynamic efficiency and complex aerodynamic response due to the platform motions. Blade pitch technology is an important method to improve the aerodynamic performance and three-dimensional flow characteristics of VAWTs. The rotation speed and blade azimuth are important factors that determine the blade pitch scheme. In this paper, the computational fluid dynamics (CFD) is implemented to systematically investigate the influence of blade pitch on the power coefficient and flow characteristics of VAWTs under different tip speed ratios (TSRs). The aerodynamic loads of VAWTs under the coupling of blade pitch and prescribed platform motions (a simplified representation without considering aero-hydro-structural coupling) are analyzed. The blade pitch scheme under various TSRs is proposed. When the TSR is relatively low (e.g., TSR <3.8), the blade pitches clockwise and counterclockwise on the upstream and downstream, respectively, to improve dynamic stall and tip loss effect, which increases the power coefficient. When the TSR is relatively high (e.g., TSR>3.8), the blade pitches counterclockwise and clockwise on the upstream and downstream, respectively, which increases the energy capture capability, but also enhances the tip loss effect and blade wake interaction. When TSR = 6.0, blade pitch can increase the maximum power coefficient of turbine by 28.2%. The prescribed platform surge motion slightly reduces power coefficient under pitch control, while prescribed platform pitch motion improves power coefficient with blade pitch. These results are obtained under idealized kinematic conditions and should not be interpreted as a fully coupled floating turbine analysis.