Performance improvement of adaptive flap on flow separation control and its effect on VAWT

Flow separation on blades is the main factor to reduce the power efficiency of vertical axis wind turbine (VAWT). A bio-inspired flow control device called adaptive flap is considered to have a good adaptability in mitigating the flow separation. The present study investigated the adaptive flap in terms of improving its performance and exploring its effect on VAWT by the Computational Fluid Dynamics (CFD) method combining the SST k-ω turbulence model. Firstly, a static flap with adjustable flap angles was installed on a static airfoil to explore the influence of the flap angle on the flap performance. Then, to improve the performance of the free rotating flap, a linear torque related to the aerodynamic moment acting on the static flap was proposed to constrain the flap. Besides, another torque composited from the aerodynamic moment distribution was proposed to give full control of the flap. The verification results showed that the two torques both worked in two typical airfoil flow separation processes, and the composite torque performed better. Finally, the rotating flaps improved by the composite torque were installed on blades of a VAWT. The simulation results showed that the flap sensibly improved the power coefficient of the VAWT at tip speed ratios (TSRs) of 0.6 and 1.2, providing a solution to slow down the flow separation in WAWT. •A linear torque and composite torque were proposed to constrain the free rotating flap to improve its performance.•The performance was improved and the composite torque has a better performance.•The flap can slow down the flow separation in VAWT and increase the power coefficient.