The Impact Of Blade Thickness On The Structural And Aerodynamics Performance Of A Morphing Wind Turbine Blade

The increasing demand for "clean" energy has become a global issue that triggers the rapid growth of renewable energy development. Engineers and designers envisage new technology to improve the performance of wind energy systems. In order to contribute to the development of renewable energy, it is important to discover the most effective type of morphing wind turbine blade. To optimize the design of a wind turbine, it requires extensive study of the interaction between the aerodynamic forces induced by the wind field and the structural response of the wind turbine blade. Coupled fluid-structure interaction (FSI) modeling can provide details about the behaviors of a morphing wind turbine blade. The two main techniques for solving the fluid-structure interaction (FSI) problem are the segregated-coupled and fully-coupled approaches. Since most of the past studies are mainly focused on the segregated-coupled approach, this study attempts to investigate the aerodynamics and structural impact of blade thickness on a morphing wind turbine blade using the fully-coupled approach. Three symmetrical morphing airfoils selected in this study are NACA 0012, NACA 0018 and NACA 0024 representing different thicknesses. These three different airfoil profiles are subject to a fixed wind speed at various attack angles from 2 to 20 degree in twodegree increments. Reynolds number of Re = 5.0 x 105 is used in all cases. Three different Young's modulus values are E1 = 1.64 x 105 Pa, E2 = 2.46 x 105 and E3 = 3.29 x 105 used to represent different material flexibility. There are a total of 90 simulation morphing airfoil models being generated. This study shows that symmetrical morphing airfoil in HAWT can improve drag and lift-drag ratio in the post-stall region. However, the benefits of the morphing effect diminish as airfoil thickness increases due to the higher bending resistance in thicker airfoil. The presented results prove that it is unnecessary to have thick root section for a wind turbine since a morphing airfoil can both increase aerodynamics performance in the post-stall region and alleviate stress loading to withstand strong wind.

Wind energy is gaining critical ground in the area of renewable energy, with wind energy being predicted to provide up to 8% of the world’s consumption of electricity by 2021. Advances in wind turbine blade design and materials reviews the design and functionality of wind turbine rotor blades as well as the requirements and challenges for composite materials used in both current and future designs of wind turbine blades. Part one outlines the challenges and developments in wind turbine blade design, including aerodynamic and aeroelastic design features, fatigue loads on wind turbine blades, and characteristics of wind turbine blade airfoils. Part two discusses the fatigue behavior of composite wind turbine blades, including the micromechanical modelling and fatigue life prediction of wind turbine blade composite materials, and the effects of resin and reinforcement variations on the fatigue resistance of wind turbine blades. The final part of the book describes advances in wind turbine blade materials, development and testing, including biobased composites, surface protection and coatings, structural performance testing and the design, manufacture and testing of small wind turbine blades. Advances in wind turbine blade design and materials offers a comprehensive review of the recent advances and challenges encountered in wind turbine blade materials and design, and will provide an invaluable reference for researchers and innovators in the field of wind energy production, including materials scientists and engineers, wind turbine blade manufacturers and maintenance technicians, scientists, researchers and academics. 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 energy production

The simulation of flow through vertical axis wind turbine (VAWT) is characterized by unsteady flow where the blade experiences varying angles of attack and Reynolds number as it completes a cycle. Therefore, the lift generated also varies as a function of its rotational position relative to the incoming freestream velocity. In order to improve the performance of these turbines the blade can take advantage of smart materials developed for control surface actuation. The aim of this paper is to investigate the effect of morphing blades on the aerodynamic performance of the turbine blades. The study uses commercial software Ansys Fluent pressure-based solver to investigate the flow past the turbine blades by solving the 2D Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. In order to simulate the morphing blade for VAWT, a sliding mesh method is used to simulate the VAWT rotation while a user-defined function (UDF) is written for the blade morphing flexure motion. This entails the use of dynamic mesh smoothing to prevent the mesh from having negative cell volumes. Although the dynamic mesh strategy has been successful in preserving the cell quality, it has been shown that the proposed method of simulating the morphing blade on VAWT is inadequate due to unphysical solutions. Finally, the effect of morphing the blade is tested on a static airfoil case instead, where it is shown that stall is alleviated by morphing the blade trailing edge.

This chapter focuses on airfoils for wind turbine blades and their characteristics. The use of panel codes such as XFOIL and RFOIL and CFD codes for the prediction of airfoil characteristics is briefly described. The chapter then discusses the requirements for wind turbine blade airfoils and the effect of leading edge roughness and Reynolds number. After a description of how airfoils can be tested the chapter discusses methods to represent airfoil characteristics at high angles of attack. A number of methods for correcting characteristics for the effect of three-dimensional flow on the blade are presented. The chapter then discusses ways to establish a data set for blade design and concludes with a view on future research in the field of wind turbine blade airfoils.

There is a growing global demand for "clean" energy due to an increased mandate to reduce greenhouse gases. Wind energy has established itself as an economically competitive source due to major developments made in the efficiency and reliability of conversion systems. Currently, horizontal axis wind turbines (HAWTs) dominate the wind energy conversion market because of their high efficiency. However, recent advances in vertical axis conversion systems are closing the gap in efficiency. A novel flexible blade concept with the ability to morph and adapt to changing flow conditions was proposed by A. Beyene and T. Ireland, to address part load and performance issues encountered in wind energy conversion systems. The extension of these benefits to a vertical axis wind turbine (VAWT) would make wind technology a more competitive player in the energy market. A straight bladed vertical axis wind turbine (SB-VAWT) rotor was manufactured, to accommodate flexible and rigid blades. The performance and flexible behavior was studied in the department of mechanical engineering's low speed wind tunnel using a test rig that was built for this study. A mathematical model, validated using a high speed camera and finite element analysis, was developed to predict the magnitude and direction of blade morph. The results show that the coefficient of performance (CP) greatly depends on the tip speed ratio (TSR), i.e., the rigid blade has CP of 0.11 for a TSR of 1.6, whereas the morphing blade achieved a CP of 0.06 at a TSR of 1.13. Overall, the modified morphing blade has better performance at low RPMs, but the rigid blade performed better at high RPMs. It was observed that the VAWT equipped with flexible blades self-started in the majority of the experiments. The flexible blade's production of power at relatively low TSRs is a rare occurrence in the field. At high RPM, the centrifugal force overwhelmed the lift force, bending the blade out of phase in an undesired direction increasing drag and therefore reducing the CP. These results suggest that alterations to the current design must be made in order to account for the inertial forces experienced by blades in a vertical axis configuration.

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.

This chapter about biobased composites starts by presenting the most promising types of cellulose fibres; their properties, processing and preforms for composites, together with an introduction to biobased matrix materials. The chapter then presents the typical mechanical properties of biobased composites, based on examples of composites with different fibre/matrix combinations, followed by a case study of the stiffness and specific stiffness of cellulose fibre composites vs glass fibre composites using micromechanical model calculations. Finally, the chapter presents some of the special considerations to be addressed in the development and application of biobased composites.

In order to improve energy capture and reduce the cost of wind energy, in the past few decades wind turbines have grown significantly larger. As their blades get longer, the design of the inboard region (near the blade root) becomes a trade-off between competing structural and aerodynamic requirements. State-of-the-art blades require thick airfoils near the root to efficiently support large loads inboard, but those thick airfoils have inherently poor aerodynamic performance. New designs are required to circumvent this design compromise. One such design is the "biplane blade", in which the thick airfoils in the inboard region are replaced with thinner airfoils in a biplane configuration. This design was shown previously to have significantly increased structural performance over conventional blades. In addition, the biplane airfoils can provide increased lift and aerodynamic efficiency compared to thick monoplane inboard airfoils, indicating a potential for increased power extraction. This work investigates the fundamental aerodynamic aspects, aerodynamic design and performance, and optimal structural design of the biplane blade. First, the two-dimensional aerodynamics of biplanes with relatively thick airfoils are investigated, showing unique phenomena which arise as a result of airfoil thickness. Next, the aerodynamic design of the full biplane blade is considered. Two biplane blades are designed for optimal aerodynamic loading, and their aerodynamic performance quantified. Considering blades with practical chord distributions and including the drag of the mid-blade joint, it is shown that biplane blades have comparable power output to conventional monoplane designs. The results of this analysis also show that the biplane blades can be designed with significantly less chord than conventional designs, a characteristic which enables larger blade designs. The aerodynamic loads on the biplane blades are shown to be increased in gust conditions and decreased under extreme conditions. Finally, considering these aerodynamic loads, the blade mass reductions achievable by biplane blades are quantified. The internal structure of the biplane blades are designed using a multi-disciplinary optimization which seeks to minimize mass, subject to constraints which represent realistic design requirements. Using this approach, it is shown that biplane blades can be built more than 45% lighter than a similarly-optimized conventional blade; the reasons for these mass reductions are examined in detail. As blade length is increased, these mass reductions are shown to be even more significant. These large mass reductions are indicative of significant cost of electricity reductions from rotors fitted with biplane blades. Taken together, these results show that biplane blades are a concept which can enable the next generation of larger wind turbine rotors.

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.

The goal of the Blade System Design Study (BSDS) was investigation and evaluation of design and manufacturing issues for wind turbine blades in the one to ten megawatt size range. A series of analysis tasks were completed in support of the design effort. We began with a parametric scaling study to assess blade structure using current technology. This was followed by an economic study of the cost to manufacture, transport and install large blades. Subsequently we identified several innovative design approaches that showed potential for overcoming fundamental physical and manufacturing constraints. The final stage of the project was used to develop several preliminary 50m blade designs. The key design impacts identified in this study are: (1) blade cross-sections, (2) alternative materials, (3) IEC design class, and (4) root attachment. The results show that thick blade cross-sections can provide a large reduction in blade weight, while maintaining high aerodynamic performance. Increasing blade thickness for inboard sections is a key method for improving structural efficiency and reducing blade weight. Carbon/glass hybrid blades were found to provide good improvements in blade weight, stiffness, and deflection when used in the main structural elements of the blade. The addition of carbon resulted in modest cost increases and provided significant benefits, particularly with respect to deflection. The change in design loads between IEC classes is quite significant. Optimized blades should be designed for each IEC design class. A significant portion of blade weight is related to the root buildup and metal hardware for typical root attachment designs. The results show that increasing the number of blade fasteners has a positive effect on total weight, because it reduces the required root laminate thickness.