Effect of helical twist angle on the aerodynamic performance and blade dynamic characteristics of floating vertical axis wind turbines

Abstract

Due to the low fluctuation of aerodynamic torque, the helical blade floating vertical axis wind turbine (FVAWT) is a promising optimization structure compared with the traditional straight blade FVAWT. The helical twist angle plays a significant role in wind turbine design and operation. In this research, the effect of the helical twist angle on the aerodynamic performance and blade dynamic characteristics are investigated. A slack coupled modeling method is applied to model a 5 MW helical blade FVAWT system. Verification is conducted in comparison with a rigid body code and ANSYS software. Then a comparative study is conducted under seven cases with helical twist angles of 0°, 60°, 90°, 100°, 110°, 120° and 150°. The results show that helical twist angles ranging from 90° to 120° could significantly restrain the fluctuation of aerodynamic torque and suppress blade deformation. The varying regularity of blade deformation under different cases is affected by both aerodynamic force and blade stiffness characteristics. In addition, for blade deformation, 1 P and its frequency multiplication, the sum and difference frequency components of 1 P and wave frequency are observed in the amplitude spectrum. For the design of the FVAWT, the natural frequency of the blade should be far from the above frequencies to avoid resonant vibration. This study could provide a feasible mathematical method for the dynamic modeling of helical blade FVAWTs. Additionally, the range of helical twist angles recommended in this paper can be referred to when designing a helical blade.