Active flow control of vertical-axis wind turbines: Insights from large-eddy simulation and finite-time resolvent analysis

Active flow control is applied to improve the aerodynamic performance of a NACA0018 airfoil operating as a single-bladed vertical axis wind turbine (VAWT). Results computed by wall-resolved large-eddy simulations (LES) highlight the detrimental effects of the dynamic stall vortex (DSV) and trailing-edge vortex (TEV) on turbine efficiency, primarily through increased drag and energy loss. The proposed flow control strategy effectively delays flow separation and suppresses large-scale vortex formation, particularly at moderate actuation frequencies. The control parameters are grounded in bi-global stability and finite-time resolvent analyses. These techniques identify the excitation of coupling modes between shear layer and wake instabilities as a mechanism for promoting flow reattachment and preventing vorticity accumulation, ultimately leading to enhanced torque production. The control strategy is energy-efficient, consuming only 1% of the turbine's output power while yielding substantial aerodynamic performance gains. These findings demonstrate the promise of physics-informed active flow control in mitigating dynamic stall and advancing the design of next-generation VAWTs.