Rotation improvement of vertical axis wind turbine by offsetting pitching angles and changing blade numbers

To improve the power extraction performance and self-starting characteristics of the vertical axis wind turbine (VAWT), the effect of offsetting pitching angles and blade numbers on the performance of a wind-induced rotation VAWT has been systematically investigated. Different from the conventional numerical and experimental approach, the rotation velocity of the turbine is driven by the aerodynamic torque of the blade in the present study. The flow around the turbine was simulated using Fluent 6.3 code, and the governing equation of the turbine’s rotation was coupled to the code through UDF. The optimized pitching angle β was found to be of −4°, at which the maximum 5.89 and 5.14 times average power increasing were achieved for the turbine with 5-blades and 3-blades, respectively. Moreover, shorter self-starting time was also observed for the turbine with β = −4° at larger wind velocity (>9 m/s). In addition, the influence of the blade number on the performance of the turbine depended on the wind velocity. The analysis of the flow field of the turbine showed that the offsetting pitching angle and blade number could suppress or delay the vortex separation, and therefore improve the overall performance of the turbine. •The influence of pitching angle and blade number on the S-VAWT were investigated.•Maximum average extraction power increase was achieved with pitching angle β of −4°.•Self-starting time of the turbine is subject to wind-velocity and blade number.•The turbine with 5-blade and a pitching angle of −4° showed the best performance.