Active Load Control Techniques for Wind Turbines
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SANDIA REPORT SAND2008-4809 Unlimited Release Printed July 2008 Active Load Control Techniques for Wind Turbines Dale Berg, Scott J. Johnson, C.P. “Case” van Dam Prepared by Sandia National Laboratories Albuquerque, New Mexico 87185 and Livermore, California 94550 Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000. Approved for public release; further dissemination unlimited. Issued by Sandia National Laboratories, operated for the United States Department of Energy by Sandia Corporation. NOTICE: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government, nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, make any warranty, express or implied, or assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represent that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government, any agency thereof, or any of their contractors or subcontractors. The views and opinions expressed herein do not necessarily state or reflect those of the United States Government, any agency thereof, or any of their contractors. Printed in the United States of America. This report has been reproduced directly from the best available copy. Available to DOE and DOE contractors from U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831 Telephone: (865) 576-8401 Facsimile: (865) 576-5728 E-Mail: [email protected] Online ordering: http://www.osti.gov/bridge Available to the public from U.S. Department of Commerce National Technical Information Service 5285 Port Royal Rd. Springfield, VA 22161 Telephone: (800) 553-6847 Facsimile: (703) 605-6900 E-Mail: [email protected] Online order: http://www.ntis.gov/help/ordermethods.asp?loc=7-4-0#online 2 SAND2008-4809 Unlimited Release Printed July 2008 Active Load Control Techniques for Wind Turbines Scott J. Johnson and C. P. “Case” van Dam Department of Mechanical and Aeronautical Engineering University of California One Shields Avenue Davis, CA 95616-5294 Dale E. Berg, Sandia National Laboratories Technical Manager Sandia Contract No. 360473 ABSTRACT This report provides an overview on the current state of wind turbine control and introduces a number of active techniques that could be potentially used for control of wind turbine blades. The focus is on research regarding active flow control (AFC) as it applies to wind turbine performance and loads. The techniques and concepts described here are often described as “smart structures” or “smart rotor control”. This field is rapidly growing and there are numerous concepts currently being investigated around the world; some concepts already are focused on the wind energy industry and others are intended for use in other fields, but have the potential for wind turbine control. An AFC system can be broken into three categories: controls and sensors, actuators and devices, and the flow phenomena. This report focuses on the research involved with the actuators and devices and the generated flow phenomena caused by each device. 3 Disclaimer: Given the nature of research in a progressive field such as wind energy, it is very difficult to mention every potential AFC device and to report precisely on all of the past and up-to-date findings. If a device or research paper is not mentioned within, it is because it was not found during the literature survey. Publications up through 2007 were used in this report. 4 TABLE OF CONTENTS ABSTRACT 3 TABLE OF CONTENTS 5 TABLE OF FIGURES 8 NOMENCLATURE 11 1 INTRODUCTION 13 1.1 Background ___________________________________________________13 1.2 Wind Turbine Control___________________________________________15 1.3 Developments in Wind Turbine Operation for Load Control___________18 1.4 Investigations into New Control Methods ___________________________19 1.4.1 Advanced Blade Pitch Control_________________________________20 1.4.2 Blade Twist Control_________________________________________22 1.4.3 Variable Diameter Rotor _____________________________________23 1.4.4 Active Flow Control ________________________________________26 2 ACTIVE FLOW CONTROL 27 2.1 Flow Control Methodology _______________________________________27 2.2 Flow Control Categories _________________________________________29 2.3 Flow Control on Wind Turbines __________________________________30 3 FLOW CONTROL DEVICES 33 3.1 Traditional Trailing-Edge Flaps___________________________________40 3.1.1 Description________________________________________________40 3.1.2 Classification ______________________________________________41 3.1.3 Background _______________________________________________41 3.1.4 Wind Turbine Control _______________________________________42 3.2 Nontraditional Trailing-Edge Flaps________________________________42 3.2.1 Description________________________________________________42 3.2.2 Classification ______________________________________________45 3.2.3 Background _______________________________________________45 3.2.4 Wind Turbine Control _______________________________________50 3.3 Microtabs _____________________________________________________51 3.3.1 Description________________________________________________51 3.3.2 Classification ______________________________________________52 3.3.3 Background,,_______________________________________________52 3.3.4 Wind Turbine Control _______________________________________59 3.4 Miniature Trailing-Edge Effectors (MiTEs) _________________________59 3.4.1 Description________________________________________________59 3.4.2 Classification ______________________________________________60 5 3.4.3 Background _______________________________________________60 3.4.4 Wind Turbine Control _______________________________________63 3.5 Microflaps_____________________________________________________63 3.5.1 Description________________________________________________63 3.5.2 Classification ______________________________________________64 3.5.3 Background _______________________________________________64 3.5.4 Wind Turbine Control _______________________________________65 3.6 Active Stall Strips_______________________________________________67 3.6.1 Description________________________________________________67 3.6.2 Classification ______________________________________________67 3.6.3 Background _______________________________________________67 3.6.4 Wind Turbine Control _______________________________________69 3.7 Vortex Generators ______________________________________________70 3.7.1 Description________________________________________________70 3.7.2 Classification ______________________________________________71 3.7.3 Background _______________________________________________71 3.7.4 Wind Turbine Control _______________________________________74 3.8 Blowing and Suction ____________________________________________75 3.8.1 Description________________________________________________75 3.8.2 Classification ______________________________________________77 3.8.3 Background _______________________________________________77 3.8.4 Wind Turbine Control _______________________________________78 3.9 Circulation Control _____________________________________________79 3.9.1 Description________________________________________________79 3.9.2 Classification ______________________________________________79 3.9.3 Background,,,, ,,.,,,____________________________________________79 3.9.4 Wind Turbine Control _______________________________________81 3.10 Plasma Actuators _______________________________________________82 3.10.1 Description________________________________________________82 3.10.2 Classification ______________________________________________85 3.10.3 Background _______________________________________________85 3.10.4 Wind Turbine Control _______________________________________89 3.11 Vortex Generator Jets ___________________________________________91 3.11.1 Description,,,_______________________________________________91 3.11.2 Classification ______________________________________________91 3.11.3 Background _______________________________________________91 3.11.4 Wind Turbine Control _______________________________________95 3.12 High-Frequency Micro Vortex Generators__________________________96 3.12.1 Description________________________________________________96 3.12.2 Classification ______________________________________________96 3.12.3 Background _______________________________________________96 3.12.4 Wind Turbine Control _______________________________________99 3.13 Synthetic Jets _________________________________________________100 3.13.1 Description_______________________________________________100 3.13.2 Classification _____________________________________________100 3.13.3 Background ,,, ,,____________________________________________101 6 3.13.4 Wind Turbine Control ______________________________________103 3.14 Active Flexible Wall____________________________________________104 3.14.1 Description_______________________________________________104