Microcylinder and slot combination for flow separation control over a wind turbine airfoil

This study explores a novel passive flow control strategy combining a microcylinder and slot configuration to mitigate flow separation over an S809 wind turbine airfoil under stall conditions at a Reynolds number of 106. Numerical simulations are conducted using the Reynolds-averaged Navier–Stokes (RANS) approach. The primary objectives are to (i) reduce or eliminate the flow separation region, (ii) enhance aerodynamic performance, and (iii) assess the effectiveness of combining two passive control techniques. The study evaluates the effects of microcylinder diameter, relative position to the leading edge, and the gap-to-diameter ratio (G/D). Results indicate that placing the microcylinder too close to the suction surface can harm aerodynamic performance. However, an optimized microcylinder position effectively suppresses flow separation and improves aerodynamic coefficients for angles of attack (AoA) between 16° and 24°. When combined with strategically positioned slots, the optimized configuration achieves a 97.47% reduction in the separation region and a 16.83% improvement in lift-to-drag ratio compared to the microcylinder alone at 24° AoA. The study also highlights the underlying flow control mechanisms contributing to separation suppression. Although this method proves effective at high AoAs, it incurs a drag penalty at lower AoAs, leading to a reduced lift-to-drag ratio compared to the baseline airfoil. These findings demonstrate the potential and limitations of the proposed microcylinder-slot combination for aerodynamic performance enhancement in wind turbine applications.