Computational analysis of multielement airfoils for wind turbines

Multielement airfoil configurations have shown promise in improving the aerodynamic and structural characteristics of the inboard section of megawatt-scale wind turbine blades by increasing the lift coefficients and lift-to-drag ratios. Steady-state, two-dimensional CFD calculations were carried out for a closely-coupled three-element airfoil system with one main element and two flaps at a Reynolds number of 1,000,000, and a well-separated four-element airfoil system with an additional strut at a Reynolds number of 975,000. The two multielement airfoil systems were designed for the inboard section of a 10 MW-scale wind turbine. Several configurations of the two systems were simulated with varying flap deflection, gap, and overhang. Simulations were performed with ANSYS FLUENT, a hybrid grid Navier-Stokes solver. Computational results were obtained using the four-equation Langtry-Menter Shear Stress Transport (SST) Transition turbulence model. Lift and drag coefficients were computed in an attempt to understand the effect of gap, overhang, and flap deflection on the multielement airfoil system performance. Wake bursting, a multielement airfoil phenomenon, was analyzed in detail by visualizing off-the-surface flow downstream of the airfoil. Two-dimensional wind tunnel simulations of the closely-coupled system were carried out to analyze the effect of wind tunnel walls on the lift, drag and wake characteristics of the multielement airfoil system