Investigation of pitch angles on the aerodynamics of twin-VAWT under staggered arrangement

Abstract

The potential applications of twin vertical axis wind turbines (VAWTs) in oceanic wind energy harvesting have drawn increasing attention. Previous researches have focused on the influence of relative location, rotational direction, tip speed ratio, etc. on the power output of this system. However, limited studies have been done to uncover the effect of pitch angles on their aerodynamic performance, especially under staggered arrangements where the blade-vortex interaction remarkably occurs. In the current study, the methods of computational fluid dynamics are used to simulate the changes of power coefficients of the twin staggered H-rotors with their pitch angles. With a relative distance of 1.6 times diameter and a relative angle of 30 °, the rotors are operated at the optimal tip speed ratio in a co-rotating direction. Totally 49 cases are conducted to investigate the pitch angle range from −6° to 0° in both rotors. It is found that the changes in pitch angle of the target rotor will affect the performance of itself and the other rotor with fixed pitch angle. Within the specified pitch range, due to the influence of the other rotor, the largest difference in power performance reaches 4.79% for the upstream rotor, and 7.04% for the downstream one. In addition, the aerodynamic mechanism is comprehensively analysed through the comparisons among velocity, vorticity and pressure fields. The findings of the current study is helpful to provide suggestions for the design of twin-VAWT system.