A new direct design method for the medium thickness wind turbine airfoil

• A new direct design method for medium thickness wind turbine airfoil is presented based on integral expression and B-spline curve.
• An optimal mathematical model of an airfoil profiles is established.
• An improved particle swarm optimization (PSO) algorithm is proposed and is then selected to optimize the wind turbine airfoil.
• Compared with the DU91-W2-250 airfoil, the new design airfoil (named CQU-A25) exhibits better aerodynamic performance in the same case.

The newly developed integral function of airfoil profiles based on Trajkovski conformal transform theory could be used to optimize the profiles for the thin thickness airfoil. However, it is hard to adjust the coefficients of the integral function for the medium thickness airfoil. B-spline curve has an advantage of local adjustment, which makes it to effectively control the airfoil profiles at the trailing edge. Therefore, a new direct design method for the medium thickness wind turbine airfoil based on airfoil integral expression and B-spline curve is presented in this paper. An optimal mathematical model of an airfoil is built. Two new airfoils with similar thickness, based on the new designed method and the original integral method, are designed. According to the comparative analysis, the CQU-A25 airfoil designed based on the new method exhibits better results than that of the CQU-I25 airfoil which is designed based on the original method. It is demonstrated that the new method is feasible to design wind turbine airfoils. Meanwhile, the comparison of the aerodynamic performance for the CQU-A25 airfoil and for the DU91-W2-250 airfoil is studied. Results show that the maximum lift coefficient and the maximum lift/drag ratio of the CQU-A25 airfoil are higher than the ones of DU91-W2-250 airfoil in the same condition. This new airfoil design method would make it possible to design other airfoils with different thicknesses.