Numerical study of a passive-pitch shield for the efficiency improvement of vertical axis wind turbines

The efficiency of a vertical axis wind turbine (VAWT) can be improved by placing a shield or deflector upstream of the turbine to reduce the negative torque on the blade. However, previous studies mainly focused on fixed shields or deflectors, and the performance of the VAWT was significantly affected by the wind direction. Considering this, this paper proposed a novel passive-pitch shield (PPS) which consists of two simple plates and could passively adjust its pitch angle according to the wind direction, so that the VAWT could operate with high efficiency under any wind directions. Two-dimensional transient CFD simulations were carried out to quantitatively analyze the influence of the PPS on the performance of the VAWT. The influence of PPS on the VAWT was explained in depth from the perspective of flow structures. Simulations were also performed to verify the passive pitch capability of the PPS and good results were obtained. To further improve the performance of the VAWT, several types of PPSs were compared. It was found that the power coefficient of the VAWT was increased by 46.32%.