In this study, the influences of pitch motion on the aerodynamics of a FO-VAWTs are investigated. The commercial computational fluid dynamics solver STAR-CCM+ is used to perform the simulations. The turbulence model of improved delayed detached eddy simulation is employed. The results show that the pitch motion can increase the power output of the rotor, and lead to the stronger blade-wake interaction. In addition, the variation ranges of torque, thrust, and lateral force of the rotor and tangential forces coefficient and normal coefficient of the blade can be extended to different extent under pitch motion with different periods and amplitudes.
Nowadays, a growing number of energy demands have led to the renewable energy achieving much attention. As one of the renewable energy resources, wind power is widely used in the world due to the cleanness without pollution and easy access (Mckenna et al., 2016). In recent years, the large scale floating offshore wind turbines (FOWTs) are becoming the attractive type as they can get offshore wind power with larger speed and lower turbulence when compared to the onshore wind turbines (Borg et al., 2014; Tran and Dong, 2015). Nevertheless, the FOWTs may face a series of technical problems, such as aerodynamics, hydrodynamics, mooring line and structural dynamics, and coupled modelling approaches (Borg and Kolios, 2014). In contrast to the horizontal axis wind turbines (HAWTs), vertical axis wind turbines (VAWTs) have the simpler profile of blades, no need of yaw devices, lower installation and maintenance costs, and less aerodynamic noise (Tjiu et al., 2015). In view of this, in the present study we focus on the unsteady aerodynamic forces of a floating offshore vertical axis wind turbine (FO-VAWT) in periodic pitch motion of the platform.
There have been some publications investigating the aerodynamics of HAWTs in a certain degree of freedom (DOF) movement. Wherein, the influences of surge motion on unsteady aerodynamic performance of the floating HAWTs are simulated by using the computational fluid dynamics (CFD), and the changing aerodynamic forces are compared with the results obtained by the FAST, showing a good consistency (Tran & Kim, 2016). The unsteady aerodynamic analysis of a floating HAWT in platform pitching motion is also conducted by using the CFD method and the FAST software (Tran & Kim, 2015). It is shown that the aerodynamic forces are sensitive to the motion of the platform. However, the analysis of the aerodynamic performance of the OF-VAWTs in a certain DOF motion is hardly to be found. Understanding the aerodynamic loads changing with the different amplitudes and periods of a single motion may be beneficial to the design of the wind turbines. Thus, the present study will be generated by considering these reasons.