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. - Reviews the design and functionality of wind turbine rotor blades - Examines the requirements and challenges for composite materials used in both current and future designs of wind turbine blades - Provides an invaluable reference for researchers and innovators in the field of wind

Small wind turbine blades share a number of features with large blades, but have some important differences. The two main differences are their much higher rotational speed, which causes more fatigue cycles and higher yaw moments, and their operation at low Reynolds number, which means that thick aerofoil sections cannot be used near the root. This chapter discusses the design challenges arising from these differences, the materials commonly used for blade manufacture, and the fatigue testing of small blades. The use of timber is highlighted for very small blades, and fibre-reinforced composite manufacture of larger ones is discussed in terms of sustainability, conformity of manufactured shape, and fatigue behaviour.

An overview of the current and future trends in wind turbine blade structural design process is presented. The main design principles and failure mechanisms of blades in operation are assessed and explained through an industry point of view, in a realistic manner. A number of failure modes which are not addressed sufficiently in the certificate guidelines are presented. An example on how to use the new design philosophy is presented. The manufactured prototype is a 44m long load carrying spar and the weight is reduced by 40%.

Aeroelasticity concerns the interaction between aerodynamics, dynamics and elasticity. This interaction can result in negatively or badly damped wind turbine blade modes, which can have a significant effect on the turbine lifetime. The first aeroelastic problem that occurred on commercial wind turbines concerned a negatively damped edgewise mode. It is important to ensure that there is some out-of-plane deformation in this mode shape to prevent the instability. For larger turbine blades with lower torsional stiffness and the possibility of higher tip speeds for the offshore designs, classical flutter could also become relevant. When designing a wind turbine blade, it is therefore crucial that there is enough damping for the different modes and that there is no coincidence of natural frequencies with excitation frequencies (resonance). An effective aeroelastic analysis is also important, and the tools used for such an analysis must include the necessary detail in the structural model.

This chapter discusses surface layer protection for wind turbine rotor blades. The surface protection and coating can be a gelcoat or a paint and can be made of unsaturated polyester, epoxy, polyurethane or acrylic. As wind turbines are often erected in harsh climates, the blade surface will be exposed to conditions that cause erosion and wear. There are tests to measure resistance against these attacks, and the surface is designed to minimize damage to the blade caused by the environment. By using existing standards for surface layers for offshore use and for helicopters, it has been found that a combination of accelerated tests for UV degradation, chemical attack and wear give a complete picture of the performance of surface layers.

This chapter deals with loads on wind turbine blades. It describes the load generating process, wind fields, and the concepts of stresses and strains. Aerodynamic loads, loads introduced by inertia, gravitation and gyroscopic effects, and actuation loads are discussed. The loading effects on the rotor blades and how they are interconnected with the dynamics of the turbine structure are highlighted. There is a discussion on how stochastic loads can be analysed and an outline of cycle counting methodology. The method of design verification testing is briefly described.

This chapter describes the process of aerodynamic rotor design for horizontal axis wind turbines. Apart from describing the state-of-the-art, it presents the mathematical models used, explains how airfoil and rotor control choice are decided and lists common design constraints. An example is used to illustrate the rotor design process, covering all the main aspects from choice of rotor size, airfoil types and number of blades to the exact aerodynamic shape of the blades. At the end of the chapter there is a summary of future trends and sources of further information.

The chapter discusses the topic of probabilistic analysis of wind turbine blades. First, structural analysis models, the definition of ‘failure’ and the treatment of random variables will be explored, focusing on the challenges involved in a probabilistic design depending on the choices made during each step. Next, the various probabilistic methods (Monte Carlo method, first-order reliability method, Edgeworth expansion method, response surface method) will be described. Issues arising out of the use of composite material structures, in applications such as wind turbine blades, as well as other aspects relating to wind energy applications will be highlighted, and techniques will be discussed through examples.

Composites have been the material of choice for wind turbine blade construction for several decades. This chapter explains why. It also shows how wind turbine blade materials and our understanding of their fatigue behaviour have developed recently, and the gaps that still exist in the knowledge. The chapter discusses why fatigue is a predominant design driver for wind turbine blades. The main structural elements of the blade (load bearing components and aerodynamic shell) are considered in terms of material and design requirements, and fundamental research questions are addressed. Finally, there is a comment on current and future trends, as well as a list of recommended reading.

An overview of the micromechanics of materials methods and approaches that can be used for the modelling of wind turbine blade composites is given in this chapter. Using the various modelling methods reviewed here, the strength, stiffness and lifetime of composite materials can be predicted and the suitability of different groups of materials for applications in wind turbine blades can be analysed. The effects of interface and matrix properties, fibre clustering and nanoreinforcement on the strength and lifetime of composites are studied in a number of simulations, and some examples of the analysis of microstructural effects on the strength and fatigue life of composites are provided.