Aerodynamic performance analysis of slotted airfoils for application to wind turbine blades

• The optimum value of lift-over-drag ratio was obtained when the slot is located just upstream of the separation point.
• There is an optimal value of slot width and an increase in this value will reduce performance.
• The flow control efficiency is affected mostly by flow velocity and less by the corresponding mass flow.
• The aerodynamic efficiency reaches its maximum value when the slope became less stiff.
• The control system improves aerodynamic performance only over a specific range of angle of attack.

In this paper we explore the improvement of aerodynamic characteristics of wind turbine airfoils under stall conditions through passive boundary layer control using slots. Baseline S809 airfoil was modified based on CFD calculations. An extensive 2D-numerical study has been done to analyze the effects of slot׳s location, width and slope and the best configuration was determined. Simulations were done using steady RANS equations; the turbulence closure model has been chosen among four possible choices (standard kk–εε, Spalart–Allmaras, kk–ωω and kk–ωωSSTSST) based on comparison with experimental results. The lift and drag coefficients and lift-over-drag ratio are compared for the different configurations. The results show that the control system improves aerodynamic performance only over a specific range of angles of attack. However, a significant penalty is observed on the airfoil efficiency for the final configuration, this penalty results from higher drag than the baseline airfoil at low angles of attack. At moderate and high angles of attack, from 10° to 20°, the slot configuration outperforms the baseline configuration.