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OCR for page R1
Assessment of Research Needs for Wind Turbine Rotor Materials Technology
ASSESSMENT OF RESEARCH NEEDS FOR WIND TURBINE ROTOR MATERIALS TECHNOLOGY
Committee on Assessment of Research Needs for Wind Turbine Rotor Materials Technology
Energy Engineering Board
Commission on Engineering and Technical Systems
National Research Council
NATIONAL ACADEMY PRESS
Washington, D.C.
1991
OCR for page R2
Assessment of Research Needs for Wind Turbine Rotor Materials Technology
NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.
This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.
The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Frank Press is president of the National Academy of Sciences.
The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White is president of the National Academy of Engineering.
The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Samuel O. Thier is the president of the Institute of Medicine.
The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Frank Press and Dr. Robert M. White are chairman and vice chairman, respectively, of the National Research Council.
This report and the study on which it is based were supported by Contract No. DE-AC04-89AL58181 between the U.S. Department of Energy and the National Academy of Sciences-National Research Council.
Library of Congress Catalog Card No. 91-60990
International Standard Book Number 0-309-04479-0
NAT S-324
Additional copies of this report are available from:
National Academy Press
2101 Constitution Avenue, N.W. Washington, D.C. 20418
Printed in the United States of America
OCR for page R3
Assessment of Research Needs for Wind Turbine Rotor Materials Technology
COMMITTEE ON ASSESSMENT OF RESEARCH NEEDS FOR WIND TURBINE ROTOR MATERIALS TECHNOLOGY
GEORGE E. DIETER (Chairman), Dean,
College of Engineering, University of Maryland, College Park, Maryland
JAMIE CHAPMAN, Power Systems Consultant,
Boston, Massachusetts
H. THOMAS HAHN,
Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, Pennsylvania
DEWEY H. HODGES,
School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, Georgia
CHARLES W. ROGERS,
Bell Helicopter Textron, Inc., Fort Worth, Texas
LENA VALAVANI,
Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, Massachusetts
MICHAEL D. ZUTECK, Consultant,
Kemah, Texas
National Research Council Staff
KAMAL J. ARAJ, Study Director,
Energy Engineering Board
THERESA A. FISHER, Study Assistant (to April 1990)
JAN C. KRONENBURG, Study Assistant (to February 1991)
ENERGY ENGINEERING BOARD
JOHN A. TILLINGHAST (Chairman),
Tiltec, Portsmouth, New Hampshire
DONALD B. ANTHONY,
Bechtel Corporation, Houston, Texas
RICHARD E. BALZHISER,
Electric Power Research Institute, Palo Alto, California
BARBARA R. BARKOVICH, Barkovich and Yap, Consultants,
San Rafael, California
JOHN A. CASAZZA, CSA Energy Consultants,
Arlington, Virginia
RALPH C. CAVANAGH,
Natural Resources Defense Council, San Francisco, California
DAVID E. COLE,
University of Michigan, Ann Arbor, Michigan
H. M. (HUB) HUBBARD,
Midwest Research Institute (retired), Golden, Colorado
ARTHUR E. HUMPHREY,
Lehigh University, Bethlehem, Pennsylvania (to February 1991)
CHARLES IMBRECHT,
California Energy Commission, Sacramento, California
CHARLES D. KOLSTAD,
University of Illinois, Urbana, Illinois
HENRY R. LINDEN,
Gas Research Institute, Chicago, Illinois
JAMES J. MARKOWSKY,
American Electric Power Service Corporation, Columbus, Ohio (to February 1991)
SEYMOUR L. MEISEL,
Mobile R&D Corporation (retired), Princeton, New Jersey
DAVID L. MORRISON,
The MITRE Corporation, McLean, Virginia
MARC H. ROSS,
University of Michigan, Ann Arbor, Michigan
MAXINE L. SAVITZ,
Garrett Ceramic Component Division, Torrance, California
HAROLD H. SCHOBERT,
Pennsylvania State University, University Park, Pennsylvania
GLENN A. SCHURMAN,
Chevron Corporation, San Francisco, California
JON M. VEIGEL,
Oak Ridge Associated Universities, Oak Ridge, Tennessee
BERTRAM WOLFE,
GE Nuclear Energy, San Jose, California
OCR for page R4
Assessment of Research Needs for Wind Turbine Rotor Materials Technology
Staff
ARCHIE L. WOOD, Executive Director,
Commission on Engineering and Technical Systems, and
Director,
Energy Engineering Board (to January 1991)
MAHADEVAN (DEV) MANI, Director, Energy Engineering Board
KAMAL J. ARAJ, Senior Program Officer
ROBERT COHEN, Senior Program Officer (retired)
GEORGE LALOS, Senior Program Officer
JAMES J. ZUCCHETTO, Senior Program Officer
JUDITH A. AMRI, Administrative/Financial Assistant
THERESA M. FISHER, Administrative Secretary
JAN C. KRONENBURG, Administrative Secretary
PHILOMINA MAMMEN, Administrative Secretary
NANCY WHITNEY, Administrative Secretary
OCR for page R5
Assessment of Research Needs for Wind Turbine Rotor Materials Technology
PREFACE
Wind-driven power systems represent a renewable energy technology that is still in the early stages of development. These wind power plants installed in the early 1980s suffered structural failures chiefly because of incomplete understanding of the wind forces (especially the turbulence component) acting on these large structures and in some cases because of poor quality in manufacture. Failure of the rotor blades was one of the principal and most serious structural failures. Failures from these causes are now somewhat better understood. Another limitation to economical achievement of the potential of wind energy is uncertainty about the long-term response of wind turbine rotor materials to the turbulent stochastic loadings to which they are subjected. These structures can be subjected to as many as a billion stress cycles.
In accordance with its assessment of its long-term research responsibilities, the Department of Energy requested the National Research Council to assess the research needs for wind turbine rotor technology. Such a study would assist in organizing the information about the current status of wind turbine rotor materials, their manufacture into blades, and their operation and life performance in service. Of special importance was an assessment of current materials technology and design methodologies to provide perspective for future investigations.
The Committee on Assessment of Research Needs for Wind Turbine Rotor Materials Technology was formed by the Energy Engineering Board to specifically evaluate the following issues (see Appendix A for Statement of Task):
the adequacy of existing models to predict dynamic stress patterns;
the properties of wind turbine materials in dynamic and fatigue failure;
understanding of the performance of joints, fasteners, and critical sections in relation to failure modes and fracture;
the tools needed to study these phenomena, such as computer design tools, and materials databases;
the need for special laboratory facilities, models, and prototypes to improve the design and operation of wind energy systems;
the opportunities for new materials to improve wind turbine life; the potential for improved design methods, advanced control techniques, and better manufacturing processes and advanced materials for better performance and longevity.
In addition, the committee took as its responsibility the development, in broad outline, of a research and development program that would place U.S. wind power technology in a preeminent world position.
In carrying out its assignment the committee examined an extensive literature on wind machines and wind turbine rotor materials. The emphasis of the study was on wind machines suitable for utility applications. Many U.S. experts on these subjects briefed the committee in two meetings of two-day duration (see Appendix B). The committee wishes to acknowledge with gratitude the assistance of the following individuals for their time and knowledge:
OCR for page R6
Assessment of Research Needs for Wind Turbine Rotor Materials Technology
Holt Ashley, Stanford University; Charles Carlson and Marilyn W. Wardle, E.I. duPont de Nemours & Co.; John C. Doyle, California Institute of Technology; Brant Goldsworthy, ALCOA/Goldsworthy Engineering; Richard H. Hilt, Gas Research Institute; William Holley, U.S. Windpower; Donald Hunston, National Institute for Standards and Technology; Edwin T.C. Ing; John Mandell, Montana State University; Robert C. Monroe, Hudson Products; Robert H. Monroe, Gougeon Brothers; Peter Ogle, Dow United Technologies Composite Products; Donald Pederson and Fred J. Policelli, Hercules, Inc.; Lawrence Rehfield, University of California-Davis; Forrest S. Stoddard, Alternative Energy Institute; Robin Whitehead, Northrop; Daniel F. Ancona III, Leonard J. Rogers and Jeffrey H. Rumbaugh, U.S. Department of Energy; James Tangler and Robert Thresher, Solar Energy Research Institute; and Herbert Sutherland, Sandia National Laboratories.
George E. Dieter, Chairman
Committee on Assessment of Research Needs for Wind Turbine Rotor Materials Technology
OCR for page R7
Assessment of Research Needs for Wind Turbine Rotor Materials Technology
CONTENTS
LIST OF FIGURES
ix
LIST OF TABLES
x
EXECUTIVE SUMMARY
1
1
INTRODUCTION
5
Scope and Content,
5
Wind-Driven Power Plants,
5
Why Materials Knowledge Is Critical,
8
The Evolution of Wind-Driven Power Plants,
9
The Principal Component: Wind Turbines,
12
Power Conversion Equations,
16
The Wind Environment,
19
Fatigue Cycle Accumulation,
20
References and Bibliography,
23
2
STRUCTURAL LOADING CHARACTERISTICS
25
Load Characterization,
26
Blade Failure Experience,
27
Lessons from Helicopter Experience,
27
Recommendations,
32
References and Bibliography,
33
3
MATERIALS PROPERTIES AND LIFE PREDICTION
35
Fibers,
35
Matrix Materials,
39
E-Glass/Plastic Composites,
43
Fatigue Life Prediction,
48
Toughness Considerations,
49
Wood/Epoxy Composites,
50
Recommendations,
60
References and Bibliography,
61
4
WIND TURBINE ROTOR DESIGN
67
Airfoil Evolution,
67
Aerodynamic Tip Brakes,
69
Blade Root Retention,
71
Glass-Reinforced Plastic (GRP) Blade Roots,
71
Wood/Epoxy Blade Roots,
75
Blade Joining,
75
Blade Design Considerations,
76
Fiberglass Blades,
76
Wood/Epoxy Blades,
78
Recommendations,
79
GRP,
79
Wood/Epoxy,
79
Generic,
79
References and Bibliography,
80
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Assessment of Research Needs for Wind Turbine Rotor Materials Technology
5
MANUFACTURING PROCESSES FOR ROTOR BLADES
81
Current Manufacturing Processes,
81
Blade Root End Concepts,
82
Manufacturing Methods Influence Blade Life,
82
Matrix Stress Versus Fatigue,
83
Helicopter Rotor Blade Design and Processing,
84
Manufacturing Processes Applicable to Wind Turbine Blades,
84
Resin Transfer Molding (RTM),
84
Pultrusion,
86
Fiber Placement,
87
Root End Design for Producibility,
87
Manufacturing Recommendations,
87
References and Bibliography,
89
6
ACTIVE CONTROL IN WIND TURBINES
91
The Control Problem for Wind Turbines,
91
Recent Trends in Control System Theory,
93
Existing Control Technology for Wind Turbines,
94
Role of Control Technology in the Wind Power Industry,
95
References and Bibliography,
98
7
CONCLUSIONS AND RECOMMENDATIONS
101
Conclusions,
101
Research Recommendations,
102
APPENDIX A:
STATEMENT OF TASK
105
APPENDIX B:
COMMITTEE MEETINGS AND ACTIVITIES
107
OCR for page R9
Assessment of Research Needs for Wind Turbine Rotor Materials Technology
LIST OF FIGURES
Figure 1-1
Wind power plant in Altamont Pass, California
6
Figure 1-2
World energy generation by wind power plants during 1989
10
Figure 1-3
Growth of generating capacity for California wind power plants
10
Figure 1-4
Growth of annual energy production for California wind power plants
12
Figure 1-5
Wind turbine subsystems
13
Figure 1-6
Wind turbine power curve
15
Figure 1-7
Wind flow field and turbine loads
16
Figure 1-8
Comparison of logarithmic power in the wind with a wind turbine power curve
17
Figure 1-9
Wind turbine blade control methods
19
Figure 1-10
Accumulation of fatigue cycles
22
Figure 2-1
Process necessary to analyze composite blades
29
Figure 3-1
Trends of longitudinal tensile fatigue S-N data for unidirectional composites with various fibers
38
Figure 3-2
Schematics of various fiber preforms
39
Figure 3-3
Stress-strain relationships of glass/epoxy laminates under uniaxial tension
45
Figure 3-4
Modes of damage growth in composite laminate under fatigue
47
Figure 3-5
Laminate directional properties and shear directional nomenclature
52
Figure 3-6
Wood strength change due to temperature at two moisture conditions
55
Figure 3-7
Wood moisture content versus atmospheric relative humidity
55
Figure 3-8
Effect of moisture content on laminate mechanical properties
56
Figure 3-9
Typical tensile fatigue strength of wood/epoxy laminate
56
Figure 3-10
Typical compression fatigue strength of wood/epoxy laminate
57
Figure 3-11
Typical reversed stress fatigue strength of wood/epoxy laminate
57
OCR for page R10
Assessment of Research Needs for Wind Turbine Rotor Materials Technology
Figure 4-1
Commonly used early HAWT airfoils
68
Figure 4-2
SERI advanced wind turbine airfoils
68
Figure 4-3
Nine-meter GRP wind turbine blade
70
Figure 4-4
Eleven-meter wood/epoxy blade airfoil thickness distribution and planform
70
Figure 4-5
Flanged GRP blade root design
71
Figure 4-6
Flanged root design limitation due to steel/GRP strain incompatibility
73
Figure 4-7a
Bonded steel root tube GRP hub design
74
Figure 4-7b
Wood/epoxy blade root
74
Figure 4-8
All-wood/epoxy composite hub
76
Figure 5-1
UH-1H composite main rotor blade
85
Figure 5-2
RTM cooling tower blade
86
Figure 5-3
4BW hingeless bearingless rotor
88
Figure 6-1
Wind turbine drive train
92
LIST OF TABLES
Table 2-1
Blade Sectional Analysis Codes
30
Table 3-1
Typical Properties of Fibers
36
Table 3-2
Typical Properties of Unidirectional Composites
37
Table 3-3
Properties of Case Resins
41
Table 3-4
High-Performance Thermoplastics Used as Matrix Resins
43
Table 3-5
Trade-offs Between Thermosets and Thermoplastics as Matrices
44
Table 3-6
Typical Static Strength, Type 110 Laminate
53
Table 6-1
Control Effectors and Sensors for a Pitch Controlled Wind Turbine
92
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