Aerodynamic Validation of Wind Turbine Airfoil Models in the Virginia Tech Stability Wind Tunnel

Accurate predictions of lift and drag are critical for the design and performance evaluation of megawattscale wind turbines. Wind tunnel testing is a key component of the design process, as it complements CFD and other prediction tools. Over the last 10 years, the Virginia Tech Stability Wind Tunnel has been used extensively for aerodynamic and aeroacoustic measurements of wind turbine airfoils; however, comparisons of data from Virginia Tech and other wind tunnels showed discrepancies in lift curve slope and maximum lift coefficient. For a DU96-W-180 airfoil geometry, measurements at Virginia Tech yielded lift curve slopes 3.0% – 5.5% smaller and maximum lift coefficients 0.04–0.12 smaller than measurements from two large scale European wind tunnels. Although differences in lift curve slopes and maximum lift coefficients are not uncommon in wind tunnel testing (see McCroskey [1] and Troldborg et al. [2]), this was viewed as an opportunity to thoroughly investigate airfoil testing procedures. The goal of this work is to investigate and evaluate all aspects of airfoil model testing in the Virginia Tech Stability Tunnel, from model fabrication through data reduction. This work has validated the majority of aspects/procedures of the Virginia Tech Stability Tunnel, including the accuracy of measured reference conditions, tunnel flow quality, accuracy of model outer mold line, lift & drag repeatability, and end effects on maximum lift. The results presented in the rest of the paper highlight key findings warranting further study.