Integrated airfoil and blade design method for large wind turbines

This paper presents an integrated method for designing airfoil families of large wind turbine blades. For a given rotor diameter and a tip speed ratio, optimal airfoils are designed based on the local speed ratios. To achieve a high power performance at low cost, the airfoils are designed with the objectives of high Cp and small chord length. When the airfoils are obtained, the optimum flow angle and rotor solidity are calculated which forms the basic input to the blade design. The new airfoils are designed based on a previous in-house designed airfoil family which was optimized at a Reynolds number of 3 million. A novel shape perturbation function is introduced to optimize the geometry based on the existing airfoils which simplifies the design procedure. The viscous/inviscid interactive code XFOIL is used as the aerodynamic tool for airfoil optimization at a Reynolds number of 16 million and a free-stream Mach number of 0.25 near the tip. Results show that the new airfoils achieve a high power coefficient in a wide range of angles of attack (AOA) and are extremely insensitive to surface roughness. Finally, a full blade analysis using computational fluid dynamics (CFD) and blade element momentum (BEM) technique proves the reliability of the integrated design method.