Passive flow control technique for enhancing power efficiency of vertical-axis wind turbines: Leading-edge slot structure

• A novel leading-edge slot structure is proposed for realizing passive flow control on the blade surface of VAWTs. • Feasibility of applying slot structures on the suction side of the blades is demonstrated. • Knowledge of how slot structures suppress flow separation and dynamic stall is enriched. • Relatively optimal slot configuration is identified based on parametric analysis. • An average power increase of 38 % is achieved under studied operating conditions. Vertical-axis wind turbines (VAWTs) are receiving growing interest in offshore wind energy exploitation. However, they often exhibit suboptimal energy conversion efficiency, particularly at low tip speed ratios (TSRs). One critical challenge is suppressing flow separation and dynamic stall on the blades. Passive flow control techniques have shown potential in improving blade aerodynamics, yet a simple and effective approach is still desired. This study proposes a novel leading-edge slot structure aimed at enhancing the power efficiency of VAWTs without additional energy input. The structure facilitates natural suction and blowing flows on the suction side of the blades. High-fidelity computational fluid dynamics simulations incorporating a transition shear stress transport model are employed to examine turbine aerodynamics. The power performance and aerodynamic loads of VAWTs with various slotted blade designs (different start locations, 0.02 c ≤ x I ≤ 0.31 c , and end locations, 0.1 c ≤ x II ≤ 0.35 c , where c denotes the blade chord length) are compared to identify the relatively optimal slot configuration. The analysis of blade boundary layer phenomena and flow state in the slot further elucidates the flow control mechanism. Results indicate that the leading-edge slot structure significantly enhances the power efficiency of the VAWT at low TSRs. The relatively optimal slot configuration ( x I = 0.16 c, x II = 0.2 c ) yields an average power increase of 38.33 % under studied operating conditions. Laminar separation bubble bursting is delayed or even eliminated for slotted blades at low and moderate TSRs. The leading-edge slot structure also delays trailing-edge separation, suppresses dynamic stall vortex formation, and reduces shedding vortex strength, thereby increasing the blade lift-to-drag ratio. This study would facilitate the blade design of VAWTs.