Unsteady Aerodynamics Experiment Phase VI: Wind Tunnel Test Con gurations and Available Data Campaigns

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Mechanical Engineering

Report Number



National Renewable Energy Laboratory

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The primary objective of the Unsteady Aerodynamics Experiment (UAE) has been to provide information needed to quantify the full-scale, three-dimensional (3-D) aerodynamic behavior of horizontal-axis wind turbines (HAWT’s). Since 1987, this experiment has been conducted by the National Renewable Energy Laboratory (NREL) at the National Wind Technology Center (NWTC) near Golden, Colorado (Butterfield et al. 1992, Simms et al. 1999b, Hand et al. 2001). These field tests, as well as similar tests performed in Europe (Schepers et al. 1997), have shown that wind turbines undergo very complex aerodynamic response phenomena when operating in the field environment. All wind turbine design codes are based on aerodynamic forces derived from steady two-dimensional (2-D) wind tunnel airfoil test results. Field-testing has shown that 3- D effects are prevalent in wind turbine field operation. Additionally, field tests have shown that wind turbines are subjected to highly dynamic load conditions as a result of turbulent inflow and shear across the rotor plane. Separating the effects due to inflow anomalies from the effects due strictly to operation in a 3-D environment was impossible with the field data. However, wind tunnel testing provided this opportunity. The only wind tunnel sizeable enough to accommodate this 10-m-diameter wind turbine is owned and operated by the National Aeronautics and Space Administration (NASA) and is located at the NASA Ames Research Center at Moffett Field, California. This wind tunnel test section is 24.4 m x 36.6 m (80 ft x 120 ft).

The purpose of this wind tunnel test was to acquire accurate quantitative aerodynamic and structural measurements on a wind turbine, geometrically and dynamically representative of full- scale machines, in an environment free from pronounced inflow anomalies. These data will be exploited to develop and validate enhanced engineering models for designing and analyzing advanced wind energy machines. A Science Panel meeting was held by NREL for the purpose of identifying wind tunnel operating conditions that would yield data needed to validate the semiempirical models currently used to simulate the effects of dynamic stall and 3-D responses (Simms et al. 1999a). After completion of the wind tunnel test, another Science Panel meeting was called in which participants modeled specific wind tunnel test configurations. The model predictions were compared with the wind tunnel test measurements (Simms et al. 2001).

The UAE research turbine measures several quantities that provide the type of data required for validation of these semiempirical models. Blade surface pressures, angle-of-attack, and inflow dynamic pressure at five span locations on one blade are the heart of the measurement system. Blade root bending moments, low-speed shaft bending moments, and nacelle yaw moment are recorded, as well as blade tip and nacelle accelerations. Positional measurements, such as nacelle yaw, rotor azimuth, and blade pitch are included. Servo-motors control the blade pitch and nacelle yaw angle with a high degree of accuracy.

This report is intended to familiarize the user with the entire scope of the wind tunnel test and to support the use of these data. Appendix A describes the turbine in detail sufficient for model development. The instrumentation, signal processing, data acquisition, and data processing are presented in Appendix B along with several detailed figures and wiring diagrams. The test matrix as completed is contained in Appendix C. Appendices D and E describe the NASA-supplied instrumentation and data files. The other appendices refer to measurement corrections, corresponding field data, and specific wind tunnel test configurations.