Advances in Wind Turbine Blade Design and Materials

Description

Advances in Wind Turbine Blade Design and Materials, Second Edition, builds on the thorough review of the design and functionality of wind turbine rotor blades and the requirements and challenges for composite materials used in both current and future designs of wind turbine blades. Advances in Wind Turbine Blade Design and Materials Copyright Contributors 1. Introduction to wind turbine blade design 1.1 Introduction 1.1.1 State of the art—Blade design 1.2 Design principles and failure mechanisms 1.2.1 Design principles 1.2.2 Failure mechanisms 1.2.2.1 Failure in the cap(s) caused by brazier loads 1.2.2.2 Buckling 1.2.2.3 Cross-sectional shear distortion Fatigue problem at the root transition area 1.2.2.4 Failure in the adhesive bondlines 1.2.2.5 Buckling driven delamination 1.2.2.6 Shear web failure 1.2.2.7 Flutter 1.2.2.8 Impact of torsional loads 1.3 Challenges and future trends in wind turbine blade design 1.3.1 Testing approach 1.3.2 Development of more advanced test methods 1.3.3 Testing parts of blades 1.3.4 Building block approach 1.3.5 Certification and standards 1.3.6 Owners' requirements 1.3.7 Finite element approach 1.3.8 Digital twin technology 1.4 Retrofit solutions 1.4.1 D-string 1.4.2 D-stiffener 1.4.3 X-stiffener 1.4.4 Floor References Further reading 2. Loads on wind turbine blades 2.1 Introduction 2.2 Types of load 2.2.1 Global loads 2.2.2 Local strains and stresses 2.2.3 Deflection and deformation 2.3 Generation of loads 2.3.1 Aerodynamic loads in operation and at idling or standstill 2.3.2 Inertia, gravitational and gyroscopic loads 2.3.3 Actuation loads 2.4 Fatigue and extreme loads 2.4.1 Assessment of ultimate loading 2.4.2 Assessment of fatigue loads 2.5 Design verification testing 2.5.1 Design verification process 2.5.2 Instrumentation 2.5.3 Calibration of global bending moment measurements 2.6 Challenges and future trends 2.6.1 Design options 2.6.1.1 Aeroelastic tailoring 2.6.1.2 Vortex generators 2.6.2 Operation strategies to mitigate loading 2.6.2.1 Individual pitch control 2.6.3 Materials issues References Sources of further information and advice 3. Aerodynamic design of wind turbine rotors 3.1 Introduction 3.1.1 State-of-the-art rotor design 3.1.2 Models and elements used in the rotor design process 3.2 The blade element momentum method 3.2.1 One-dimensional momentum theory 3.2.2 Blade element momentum theory 3.3 Important parameters in aerodynamic rotor design 3.3.1 Airfoil performance 3.4 Particular design parameters 3.4.1 Tip speed ratio 3.4.2 Size of rotor/generator 3.4.3 Rotor control 3.4.4 Design constraints 3.4.5 Choice of number of blades 3.4.6 Evaluation of the rotor design 3.5 An example of the rotor design process 3.5.1 Step 1: wind climate 3.5.2 Step 2: size of rotor/generator 3.5.3 Step 3: rotor control 3.5.4 Step 4: design constraints 3.5.5 Step 5: choice of number of blades 3.5.6 Step 6: choice of design lift and airfoils 3.5.7 Step 7: choice of design tip speed ratio 3.5.8 Step 8: one point design of blade 3.5.9 Step 9: evaluation of the blade design 3.6 Future trends 3.7 Sources of further information and advice Appendix: nomenclature Acknowledgments References 4. Aerodynamic characteristics of wind turbine blade airfoils 4.1 Introduction 4.2 Computational methods 4.2.1 Panel codes, XFOIL and RFOIL 4.2.2 Computational fluid dynamics 4.2.2.1 Investigation of airfoil contour 4.2.2.2 Mesh generation 4.2.2.3 Inspection of mesh 4.2.2.4 Boundary conditions 4.2.2.5 Turbulence model 4.2.2.6 Computing 4.2.2.7 Inspection of results 4.2.3 Panel codes versus Navier–Stokes codes 4.2.3.1 Computational speed 4.2.3.2 Time for preparation 4.2.3.3 Computational details 4.2.3.4 Comparisons to measurements 4.2.3.5 Summary 4.3 Desired characteristics 4.3.1 The velocity and forces on a blade element 4.3.2 Outboard airfoils 4.3.3 Inboard airfoils 4.4 The impact of leading edge contamination, erosion and Reynolds number 4.4.1 Effects of roughness 4.4.2 The effect of the Reynolds number 4.5 Noise 4.6 Airfoil testing 4.6.1 Setup and testing equipment 4.7 Airfoil characteristics at high angles of attack 4.8 Correction for centrifugal and Coriolis forces 4.8.1 Existing 3-D correction models 4.8.2 An example of the application of 3-D models to a wind turbine rotor with stall control 4.9 Establishing data for blade design 4.9.1 Available airfoil data 4.9.2 Establishing the data 4.10 Future trends Appendix: Nomenclature References 5. Aeroelastic design of wind turbine blades 5.1 Introduction 5.1.1 Aeroelasticity 5.1.2 Natural modes 5.2 Wind turbine blade aeroelasticity 5.2.1 Wind turbine blade modes 5.2.2 Wind turbine blade instabilities 5.2.2.1 Stall-induced instabilities 5.2.2.2 Idling and parked instabilities 5.2.2.3 Classical flutter 5.3 Blade design 5.3.1 Avoidance of resonance 5.3.2 Structural pitch angle 5.3.3 Bend twist coupling 5.3.4 Analysis 5.3.5 Aerofoils 5.4 Complete turbine design 5.5 Challenges and future trends 5.6 Sources of further information and advice References 6. Micromechanical modeling of wind blade materials 6.1 Introduction 6.2 Analytical methods of micromechanical modeling of fiber-reinforced composites: an overview 6.2.1 Analytical models of damage and strength of fiber-reinforced composites: tensile loading 6.2.2 Modeling of compressive failure of composites 6.3 Unit cell modeling of fiber-reinforcedcomposites 6.4 3D modeling of composite degradation under tensile loading 6.5 Carbon fiber-reinforced composites: statistical and compressive loading effects 6.6 Hierarchical composites with nanoengineered matrix 6.7 Conclusions, challenges, and future trends 6.8 Sources of further information Acknowledgments References Further reading 7. Fatigue as a design driver for composite wind turbine blades 7.1 Introduction 7.2 Materials in blades 7.3 Blade structure and components 7.3.1 Load-bearing components 7.3.1.1 Root and blade joint connections 7.3.2 Aerodynamic shell 7.3.2.1 Skin 7.3.3 Cost 7.4 Fundamentals of wind turbine blade fatigue 7.4.1 Significance of fatigue loading on blades 7.5 Rotor blade tests at Delft University of Technology in 1984 () 7.5.1 Number of load cycles 7.5.2 Variability of cycles 7.5.3 Contribution of each load cycle to fatigue damage 7.5.4 Need for design optimization 7.5.5 Fundamentals of fatigue modeling 7.6 Research into wind turbine blade fatigue and its modeling 7.6.1 Empirical and phenomenological fatigue modeling 7.6.2 Micromechanical modeling 7.6.3 Thick laminates 7.6.4 Extreme conditions 7.6.5 Bondlines 7.6.6 Leading- and trailing-edge reinforcement 7.7 Future trends 7.7.1 Significance of material models for blade tests 7.7.2 Probabilistic modeling 7.7.3 Structural health monitoring 7.7.4 Sustainability 7.7.5 Testing 7.7.6 Reaching the limits 7.7.7 Redundancy of supply 7.7.8 Automated production 7.7.9 Repair 7.7.10 Subcomponent research 7.8 Conclusion 7.9 Sources of further information and advice References Further reading 8. Effects of resin and reinforcement variations on Fatigue resistance of wind turbine blades 8.1 Introduction 8.2 Effects of loading conditions for glass and carbon laminates 8.3 Tensile fatigue trends with laminate construction and fiber content for glass fiber laminates 8.3.1 Materials 8.3.2 Fatigue parameters for different laminate types 8.3.3 Effects of fiber content 8.4 Effects of resin and fabric structure on tensile fatigue resistance 8.4.1 Effects of resin on multidirectional (MD) laminates 8.4.2 Effects of resin on unidirectional (UD) fabric laminates 8.4.3 Effects of resin on UD aligned strand (AS) laminates compared to UD fabric laminates 8.4.4 Effects of resin on biax laminates 8.4.5 Effects of fabric weight and structure on epoxy resin MD laminates 8.5 Delamination and material transitions 8.5.1 Ply drops in carbon and glass prepreg laminates 8.5.2 Infused complex structured coupons with ply drops 8.6 Comparison of fatigue trends for blade materials 8.7 Conclusion 8.8 Future trends 8.9 Sources of further information and advice Acknowledgments References 9. Fatigue behavior and life prediction of wind turbine blade composite materials 9.1 Introduction 9.2 Fatigue behavior of laminates under complex loading profiles 9.2.1 Fatigue experiments 9.3 Fatigue life modeling and prediction 9.3.1 Macroscopic failure theories 9.3.1.1 S–N curve formulations 9.3.1.2 Constant life diagrams 9.3.2 Strength and stiffness degradation fatigue theories 9.3.3 Fracture mechanics fatigue theories 9.3.3.1 Manipulation of fracture mechanics data 9.4 Case study: phenomenological fatigue life prediction 9.5 Summary and future trends References 10. Probabilistic design of wind turbine blades 10.1 Introduction 10.1.1 Overview of probabilistic design 10.1.2 Uncertainty modeling 10.2 Structural analysis models 10.3 Failure definition 10.3.1 Lamina failure probability 10.3.2 Laminate failure probability 10.3.3 Failure probability of the blade section 10.3.4 Failure probability against buckling 10.4 Random variables 10.4.1 Material properties under static conditions 10.4.2 Material strength properties for fatigue conditions 10.4.3 Loads 10.5 Probabilistic methods and models 10.5.1 Monte Carlo simulation method 10.5.2 Edgeworth expansion method 10.5.3 First-order reliability method 10.5.4 Response surface method 10.6 Application examples and discussion of techniques 10.6.1 Reliability under extreme loading 10.6.2 Reliability against buckling 10.6.3 Reliability against fatigue 10.7 Challenges and future trends 10.8 Sources of further information and advice References 11. Biobased composites: materials, properties, and potential applications as wind turbine blade materials 11.1 Introduction 11.2 Biobased fibers and matrix materials 11.2.1 Biobased fibers 11.2.2 Biobased matrix materials 11.3 Biobased composites 11.3.1 Glass fiber/bioresin composites 11.3.2 Bamboo fiber/epoxy composites 11.3.3 Jute fiber/bioresin composites 11.4 Case study: comparison between cellulose and glass fiber composites 11.5 Special considerations in the development and application of biobased composites 11.5.1 Fiber defects 11.5.2 Variability in fiber properties 11.5.3 Interface properties 11.5.4 Other issues References Sources of further information and advice 12. Surface protection and coatings for wind turbine rotor blades 12.1 Introduction 12.2 Fundamentals of surface protection for wind turbine blades 12.2.1 Adhesion of surface coatings 12.2.2 Selection criteria for coatings 12.2.3 Particular coating materials 12.2.3.1 Unsaturated polyesters 12.2.3.2 Epoxies 12.2.3.3 Acrylates 12.2.3.4 Vinylesters 12.2.3.5 Polyurethanes 12.3 Protection from blade icing, lightning and air traffic 12.3.1 Wind turbine blade icing 12.3.2 Lightning protection 12.3.3 Protection from air traffic 12.4 Performance testing of protection layers: an introduction 12.4.1 Performance testing considerations 12.4.2 Degradation of polymers 12.4.2.1 Weathering 12.4.2.2 Sunlight 12.4.2.3 Oxygen and humidity 12.4.2.4 Degradation mechanisms 12.4.3 Measuring the degradation of polymer systems 12.4.4 Accelerated testing: an introduction 12.4.4.1 UV tests and xenon light tests 12.4.4.2 Ozone 12.4.4.3 Combined influences 12.5 Accelerated testing of the surface coatings of wind turbine blades in practice 12.5.1 Standards 12.5.2 Selected test methods 12.5.2.1 Norsok test 12.5.2.2 Wear test 12.5.2.3 Humidity test 12.5.2.4 Chemical attack 12.5.2.5 Results of tests 12.6 Conclusions, challenges, and future trends 12.6.1 Advantages and limitations of different protection technologies 12.6.2 Challenges and future trends 12.6.2.1 New materials 12.6.2.2 Protection of the surroundings 12.6.2.3 Working environment 12.6.2.4 Test methods References Further reading 13. Design, manufacture, and testing of small wind turbine blades 13.1 Introduction 13.1.1 Background 13.1.2 Key differences between small and large blades 13.1.3 Scope and layout 13.2 Requirements for small wind turbine blades 13.3 Materials and manufacture 13.3.1 Timber 13.3.2 Fiber-reinforced composites 13.3.3 Rapid prototyping and low-volume production methods 13.4 Blade testing 13.4.1 Static testing 13.4.2 Small blade fatigue 13.4.3 Quality control 13.5 Installation and operation 13.6 Challenges and future trends Acknowledgments References 14. Wind turbine blade structural performance testing 14.1 Introduction 14.2 Test program 14.3 Types of tests 14.3.1 Static tests 14.3.2 Fatigue tests 14.3.3 Ultimate tests 14.4 Test loads 14.4.1 Static test 14.4.2 Fatigue test 14.4.2.1 Sequential single-axial, single location 14.4.2.2 Multiaxial, single location 14.5 Test details 14.5.1 Load introduction 14.5.2 Blade root clamping 14.5.3 Instrumentation 14.5.3.1 Applied force 14.5.3.2 Strains 14.5.3.3 Displacements 14.5.3.4 Accelerations 14.5.3.5 Environmental conditions 14.5.3.6 Electrical conductivity of lightning protection system 14.5.4 Conclusion References 15. Maintenance and repair of wind turbine blades 15.1 Introduction 15.2 Structural health monitoring: main approaches 15.3 COST evaluation of repair technologies 15.4 Repair technologies of wind turbine blades 15.5 Computational modeling of patch repair of wind turbine blades 15.6 Conclusions, challenges, and future trends 15.7 Sources of further information Acknowledgment References Index A B C D E F G H I J L M N O P Q R S T U V W X Y