WIND-TUNNEL TEST OF THE S814 THICK ROOT AIRFOIL

The objective of this wind-tunnel test was to verify, the predictions of the Eppler Airfoil Design and Analysis Code for a very thick airfoi l having a high maximum lift coefficient designed to be largely insens itive to leading-edge roughness effects. The 24 petcent thick S814 air foil was designed with these characteristics to accommodate aerodynami c and structural considerations for the root region of a wind-turbine blade. In addition, the airfoil's maximum lift-to-drag ratio was desig ned to occur at a high lift coefficient. To accomplish the objective, a two-dimensional wind tunnel test of the S814 thick root airfoil was conducted in January 1994 in the low-turbulence wind tunnel of the the Delft University of Technology Low Speed Laboratory, The Netherlands. Data were obtained with transition free and transition fixed for Reyn olds numbers of 0.7, 1.0, 1.5, 2.0, and 3.0 x 10(6). For the design Re ynolds number of 1.5 x 10(6), the maximum lift coefficient with transi tion free is 1.32, which satisfies the design specification. However, this value is significantly lower than the predicted maximum lift coef ficient of almost almost 1.6. With transition fixed at the leading edg e, the maximum lift coefficient is 1.22. The small difference in maxim um lift coefficient between the transition-free and transition-fixed c onditions demonstrates the airfoil's minimal sensitivity to roughness effects. The S814 root airfoil was designed to complement existing NRE L low maximum-lift-coefficient tip-region airfoils for rotor blades 10 to 15 meters in length.