Impact of double split slot geometry on aerodynamic performance of modified airfoil for wind turbine blades

Introducing a slot into an airfoil is a passive flow control technique that enhances aerodynamic performance by manipulating the boundary layers of fluid flow. This study investigates the aerodynamic performance of a novel double-split slot design using the NACA 0018 airfoil through a detailed 2D steady-state numerical analysis. A parametric study was conducted to evaluate the influence of key design parameters, including slot outlet location, outlet width, and wedge element length, on the force coefficients and the flow structure around the airfoil. Results demonstrate that the double-split slot effectively weakened the flow separation on the suction side, at moderate to higher angles of attack (15° ≤ α ≤ 30°). The optimal slot configuration achieved a lift coefficient (C_L) improvement of 118% and a drag coefficient (C_D) reduction of 49% compared to the baseline clean airfoil. Slot configurations with outlets positioned closer to the leading edge (LE), wider outlet widths, and longer split channels displayed improved performance by preventing flow detachment. Most double-split slots delayed flow separation by up to 10° in AOA. Overall, slotted airfoils demonstrated superior performance over clean airfoils at higher AOAs, making them particularly beneficial for vertical-axis wind turbine blade applications.