• • .: Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste ForewordThe Wind Technology Division of the National Renewable Energy Laboratory (NREL) is conducting exploratory research on aerodynamic devices that are intended to enhance wind-turbine rotor performance and attenuate structural loads. Desired properties of these devices include simplicity, reliability, maintainability, low cost and fail-safe design. Initial efforts have focused on the use of trailing-edge aerodynamic brakes for overspeed protection. Long-term efforts will address more aggressive and innovative strategies that have the potential to significantly advance the state of the art.The first two research projects proceeded in parallel, with considerable interaction between the principal investigators:Subcontract No. TAD-3-13400 entitled "Wind Turbine Trailing-Edge Aerodynamic Brake Design" performed by Gene A. Quandt, and Subcontract No. XAD-3-133365 entitled "Aerodynamic Devices for Wind Turbine Performance Enhancement" performed by Wichita State University (WSU).The WSU Phase-1 Report discussed the configurations studied and the attempts to identify promising alternatives through the analysis of the wind tunnel test data. The Phase-2 Report presented wind tunnel results for "spoiler-flaps" of 30%, 40% and 50% chord; for various leading-edge lip extensions; for different venting arrangements; and for different device hinge locations. Gene Quandt's subcontract report, No. TP-441-7389, focused on aerodynamic and structural design, and included preliminary design calculations for a centrifugally-actuated aerodynamic brake.As is often the case with exploratory research, these projects spawned additional follow-on studies. Wind-tunnel tests were conducted at Ohio State University (OSU) in which a pressure-tapped S809 airfoil model was tested with three trailing-edge devices: the spoiler-flap, a plain flap ("unvented aileron") and a vented plain flap ("vented aileron"). In Subcontract No. XAX-5-15217-0 entitled "Investigation of Trailing-Edge Aerodynamic Brakes", rotating-blade tests of these same configurations were conducted at the National Wind Technology Center (NWTC) with the goal of quantifying the effects of unsteadiness, blade rotation and aspect ratio, so that corrections might be applied to wind-tunnel test data for use by wind-turbine designers in the future. The results of that effort are contained in the present report. PrefaceThe information presented in this report represents a great deal of work and time. It is the product of a team effort, in every sense of the phrase.Paul Migliore and many others at the National Renewable Energy Laboratory (NREL) National Wind Technology Center (NWTC) arranged for us to conduct the atmospheric tests. As far as the authors are aware, this investigation was the fi rst where non-NREL personnel conducted their experiments independently using a NWTC turbine. The exercise was valuable, enlightening, and pleasurable. Lee Fingersh and Dave Jager, in particular, provided ...

Advanced Energy Systems (AES) Inc. conducted a conceptual study of independent pitch control using inflow angle sensors. The control strategy combined input from turbine states (rotor speed, rotor azimuth, each blade pitch) with inflow angle measurements (each blade angle of attack at station 11 of 15) to derive blade pitch demand signals. The controller reduced loads sufficiently to allow a 10% rotor extension and to reduce cost of energy 6.3%. iv ACKNOWLEDGMENTS This study was performed by a team of wind energy consultants, including Tim Olsen of Advanced Energy Systems (project manager), Eric Lang of E3-Design (principal investigator), Craig Hansen of Windward Engineering, Marvin Cheney of PS Enterprises, John VandenBosche and Terrance Meyer of Chinook Wind, and Gene Quandt. Technical and management support were provided by a National Renewable Energy Laboratory (NREL) technical review team, led by Alan Wright and Dave Simms (technical monitors), with Neil Wikstrom serving as contract administrator. David Malcolm and Dayton Griffin of Global Energy Concepts also provided substantial support in establishing and understanding the WindPACT baseline turbine and its associated design and analysis tools. Funding was made possible through the NREL Low Wind Speed Turbine Project, subcontract number RAM-2-31235 (84%), and cost-sharing by the project team members (16%). v

An investigation was undertaken to identify the aerodynamic performance of five separate trailing-edge control devices and to evaluate their potential for wind turbine overspeed control applications. A modular two-dimensional wind tunnel model was constructed and aerodynamic performance data were acquired. To further interpret their potential, the controls were evaluated using a performance analysis computer program and a generic wind turbine geometry. On the basis of the investigation results, the Spoiler-Flap control configuration was deemed best suited for turbine braking applications. This particular control exhibited a good suction coefficient behavior over a broad angle-of-attack range and good turbine braking capabilities, especially at low tip-speed ratios.

The Wind Technology Division of the National Renewable Energy Laboratory (NREL) is conducting exploratory research on aerodynamic d vices that are intended to enhance wind-turbine rotor performance and attenuate structural loads. Desired properties of these devices include simplicity, reliability, maintainability, low cost, and fail-safe design. Initial efforts have focused on the use of trailing-edge aerodynamic brakes for overspeed protection. Long-term efforts will address more aggressive and innovative strategies that have the potential to significantly advance the state of the art. • This report touches on the work performed in two projects: Subcontract No. TAD-3-13400 entitled "Wind Turbine Trailing-Edge Aerodynamic Brake Design" performed by Gene A. Quandt, and Subcontract No. XAD-3-133365 entitled "Aerodynamic Devices for Wind Turbine Performance Enhancement" performed by Wichita State University (WSU). These two projects progressed in parallel, with considerable interaction between the principal investigators. The WSU Phase 1 Report discussed the configurations studied and the attempts to identify promising alternatives through the analysis of the wind tunnel test data. The Phase 2 Report presented wind tunnel results for "spoiler-flaps" of 30%, 40% and 50% chord; for various leading-edge lip extensions; for different venting arrangements; and for different device hinge locations. Gene Quandt's subcontract report, the document you are presently reading, focuses on aerodynamic and structural design, and includes preliminary design calculations for a centrifugally actuated aerodynamic brake. As is often the case with exploratory research, these projects have spawned additional follow-on studies. Wind-tunnel tests are planned at Ohio State University in which a pressure-tapped S809 airfoil model will be tested with three trailing-edge devices: the spoiler-flap, a plain flap ("unvented aileron") and a vented plain flap ("vented aileron"). Rotating-blade tests of these same configurations will be conducted at the National Wind Technology Center (NWTC), with the goal of quantifying the effects of unsteadiness, blade rotation, and aspect ratio, so that corrections can be applied to wind tunnel test data for use by wind-turbine designers in the future. iii wind turbine design 1 7. SECURITY CLASSIFICATION

or DOE Information Bridge http://www.doe.gov/bridge/home.html Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste FOREWORDThe National Renewable Energy Laboratory's (NREL's) National Wind Technology Center is supporting the efforts of its industry partners to develop advanced, utilityscale wind turbines. Part of the research being conducted focuses on innovative components and subsystems that eventually may be incorporated into these advanced turbines. PS Enterprises, Inc. (PSE) chose to investigate a flexible, downwind, free-yaw, five-blade rotor system employing pultruded blades.Studies conducted by PSE showed that, for a given rotor solidity, increasing the number of blades reduced the rotor weight. And from previous experience with both helicopter and wind turbine rotors, it was known that the pultrusion process resulted in blades having a very low cost-per-unit-weight. Indeed, pultruded blades were employed on wind turbines by StormMaster, Windtech, Dynergy, and Bergey Windpower. However, in some cases, problems were reported with yaw instability and occasional tower strikes. Furthermore, because pultruded blades are constrained to constant cross sections, without taper or twist, they are known to suffer a degradation in aerodynamic performance. So the challenge of the PSE project was to design and test a dynamically-and structurally-stable rotor that demonstrated the anticipated weight and cost savings while maintaining reasonable aerodynamic performance.PSE assembled a diverse group of consultants from around the United States to work on the project. The expertise of the project participants included aerodynamics, mechanical design, structural dynamics and testing. They worked closely with NREL to accomplish design reviews, modal tests, blade structural tests and field tests. This approach had the effect of adding logistics challenges to the acknowledged technical difficulties.It can be said with virtual certainty that engineering projects of this nature always encounter unexpected difficulties and frequently fall short of the original goals and objectives. In this project, a gearbox failure and subsequent runaway led to an early curtailment of the field-test program. Nevertheless, PSE and its consortium of consultants, completed an exceptional amount of work, the results of which demonstrate great promise for the proposed rotor concept. And to their credit, it was completed within the negotiated budget. PREFACEThis project, supported by NREL under Subcontract No. AAA-4-12272-04, was undertaken to assess the feasibility of using pultruded blades for wind turbine rotors. It represents a more rigorous engineering investigation of pultruded wind turbine blades compared to that performed on the initial rotors using this technology. The early operating experience of these rotors, although it showed pultrusions as a promising new blade technology, was plagued with design and quality control problems. Adequate engineering analysis and component testing had not been performed du...