Flow control for high-solidity vertical axis wind turbine based on adaptive flap

•Adaptive flap for use by a high-solidity vertical axis wind turbine is developed.•Performance of the adaptive flap is studied by considering different flap lengths and locations.•Optimal parameters of the adaptive flap have been predicted.•Advantage and weakness of the adaptive flap are discussed. Adaptive flap as a new flow control technique with adaptability to the changing flow separation has recently attracted much attention. This study uses the adaptive flap to mitigate the flow separation of a vertical axis wind turbine with a high solidity of 0.75 and investigate its performance and flow control mechanism by considering different flap lengths and locations. The fluid flow is simulated using computational fluid dynamics with the shear-stress transport k-ω model, and the flap motion is calculated based on the fluid–solid interaction methodology. The results show that the flap can be adaptively raised by the backflow caused by flow separation and used to block the backflow. The blocking of the backflow alleviates the flow separation problem and increases the blades’ aerodynamic torque. However, the long flap causes a negative effect due to its inability to retract timely when the flow tends to the attached state at high tip speed ratio scenario. It is observed that the short flap can avoid this problem when it is located far from the blade leading edge. Also, the short flap located closer to the blade leading edge performs better at low tip speed ratios, even though the performance is observed to be weakened by the trailing edge vortices suppressing the flap from deployment. This study provides a technical approach and theoretical basis for better alleviating the flow separation problems in vertical axis wind turbine.