Design and wind tunnel evaluation of a symmetric airfoil series for large wind turbine applications

Using the Eppler analytic design methodology, a family of symmetric airfoils with thickness to chord ratios of 0.21, 0.25, and 0.29 has been designed for applications to large wind turbines. The airfoil series, designed for Reynolds numbers above 4 x 10/sup 6/, has a contour that maintains its thickness to the 0.7 chord position, allowing use of a deep aft spar for structural integrity. Wind tunnel tests of the 21 percent thick airfoil conducted in The Ohio State University Airfoil Test Facilities at M = 0.25 and Re = 2, 4, and 8 x 10/sup 6/ showed good agreement with predicted surface pressures and lift and drag coefficients when the angle of attack was low and the Reynolds number was 8 x 10/sup 6/. At the lowest Reynolds number, both the measured lift curve slope and the maximum lift coefficient differ significantly from theory. In the post-stall region, agreement with theory and experiment is poor, at all Reynolds numbers, verifying the need for improved analytic methods in this important flow regime.