CFD analysis of multielement airfoils for wind turbines

Multielement airfoil configurations have shown promise in improving the aerodynamic characteristics of the inboard section of megawatt-scale wind turbine blades by increasing the lift-to-drag ratios, lift coefficients, and structural efficiency. Steady-state, twodimensional CFD calculations were carried out for a closely-coupled multielement airfoil system with one main element and two flaps at a Reynolds number of 1,000,000. Five configurations of the multielement airfoil system were simulated with varying flap deflection, gap, and overhang. Simulations were performed with ANSYS FLUENT, which is a hybridgrid Navier-Stokes solver. Computational results were obtained using the four-equation Langtry-Menter Shear Stress Transport (SST) Transition turbulence model. Grid convergence studies were carried out by examining three grids with progressively higher grid resolutions and quantifying their effects on lift and drag coefficients. Computed solutions were obtained for angles of attack ranging from 9 to 20 deg. Lift and drag coefficients were computed to understand the effect of gap, overhang, and flap deflection on the multielement airfoil system performance. Wake bursting, a multielement airfoil phenomenon, was observed by visualizing off-the-surface flow downstream of the airfoil.