Aerodynamic performance optimization of vertical axis wind turbine with straight blades based on synergic control of pitch and flap

Low power efficiency is a critical reason that restricts the potential application of the vertical axis wind turbine (VAWT) in offshore engineering. Hence, efficiency enhancement is an essential topic for the VAWT design. This paper attempts to propose an improved active control strategy and a novel blade structure with a trailing-edge flap for H-type VAWT to improve the power outputs at different tip speed ratios (TSRs). The orthogonal experiment design (OED) method was applied to optimize the motion of pitch and flap at low and moderate TSRs. Subsequently, the output characteristics, including the coefficients of power, torque, tangential force, and thrust of the optimized pitch-flap (P-F) model and three other models, namely the base model, the pitch-only (P-O) model, and the flap-only (F-O) model, were compared. Besides, the flow structures and static pressure distribution on the blade surface were studied to reveal the mechanism of power increase. It was found that the synergic motion of pitch and flap could effectively suppress the flow separation and delay the dynamic stall around blade. The result indicated that enhancement of the P-F model in torque coefficient was over 130% and 60% at low and moderate TSRs compared to the base model. In addition, the synergic motion of pitch and flap was found able to reduce the load fluctuation of the VAWT. The improved active control strategy and the blade structure with a trailing-edge flap may be helpful for the potential application of the H-type VAWT in offshore engineering.