49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Jan 04 - Jan 07, 2011, Orlando, FL Dynamic Characterization of a Wind Turbine Blade Section Ashli L. Babbitt ∗ , John A. Strike † , Christopher E. Mertes ‡ , Michael D. Hind § , Manjinder J. Singh ¶ , Jonathan W. Naughton ‖ , University of Wyoming Wind Energy Research Center, Laramie, WY, 82071, USA An experiment has been performed to characterize the flow over a two-dimensional, pitching blade section by taking surface pressure measurements as well as flow-field mea- surements using PIV. This investigation was conducted in order to determine the effect of the dynamic motion associated with wind turbine blades on the flow field. Surface pressure and flow-field PIV measurements were taken with the blade set at fixed angles of attack as well as in dynamic motion through an angle of attack range of -3 ◦ to 17 ◦ at reduced frequencies, k, of 0.07 and 0.15. The results indicate that flow associated with the dynamic blade section varies greatly in comparison with the flow of the static blade over most of the angle of attack range. It became clear during this study that both surface and flow-field data are required to determine what is happening in these complex flows. I. Introduction Wind turbine reliability and efficiency is becoming more and more important due to the growth of the wind energy industry. 1 The reliability of wind turbines is currently hindered by damage to the blade structure and mechanical components caused by unsteady aerodynamic loads. Minimizing these undesirable loads will increase the reliability of wind turbines. One of the issues that is currently making blade design more difficult is that prediction results vary from experimental measurements. 2 The reason that the prediction results are unreliable is the complexity of the unsteady flows associated with horizontal axis wind turbine (HAWT) blades. The rotation of the blades causes a change in angle of attack (α) experienced by the blade at different points in its rotation due to atmospheric shear as well as operation in yawed conditions. Figure 1 shows this angle of attack variation. At location (1), the blade is located in a region of lower wind velocity closer to the ground, but as it moves to location (2), the wind velocity increases. Since the velocity of the rotor (rω, where r is the radius from the hub and ω is the angular velocity of the blade) is constant, the magnitude and direction of the relative wind velocity (U rel ) seen by the blade changes with an increase or decrease in wind velocity (U ), thus causing a change in angle of attack. This effect can be amplified when the rotor is at a yaw angle (γ ) to the wind velocity. Figure 1 shows a yaw angle in a direction that increases the angle of attack. However, as the blade rotates to the other side, the effect is reversed, resulting in a smaller angle of attack. Therefore, when the rotor is at a yaw angle, a larger angle of attack range is experienced by the blade. In order to improve wind turbine design, it is necessary to understand how this dynamic motion affects the blade aerodynamics. Turbine blades are currently designed using static wind tunnel data with corrections that attempt to account for dynamic effects. However, this design approach tends to underpredict blade loading, 3 and therefore dynamic experiments are needed to study these complex blade flows. A range of dynamic tests have been carried out in the past (see for example references 4 and 5) but many of them are not at relevant conditions for a wind turbine blade, and others lack comprehensive flow-field data. Fully ∗ Graduate Research Assistant, Mechanical Engineering Department, Student Member AIAA † Graduate Research Assistant, Mechanical Engineering Department, Student Member AIAA ‡ Graduate Research Assistant, Mechanical Engineering Department, Student Member AIAA § Assistant Research Scientist, Mechanical Engineering Department, Member AIAA ¶ Associate Research Scientist, Mechanical Engineering Department, Member AIAA ‖ Associate Professor, Mechanical Engineering Department, Associate Fellow AIAA 1 of 13 American Institute of Aeronautics and Astronautics 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 4 - 7 January 2011, Orlando, Florida AIAA 2011-350 Copyright © 2011 by Jonathan W. Naughton. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.