Thomas D. Ashwill

ALTERNATIVE COMPOSITE MATERIALS FOR MEGAWATT-SCALE WIND TURBINE BLADES: DESIGN CONSIDERATIONS AND RECOMMENDED TESTING

As part of the U.S. Department of Energy’s Wind Partnerships for Advanced Component Technologies program, Global Energy Concepts LLC (GEC) is performing a study concerning blades for wind turbines in the multi-megawatt range. Earlier in this project constraints were identified to cost-effective scaling-up of the current commercial blade designs and manufacturing methods, and candidate innovations in composite materials, manufacturing processes and structural configurations were assessed. In the present work, preliminary structural designs are developed for hybrid carbon fiber / fiberglass blades at system ratings of 3.0 and 5.0 megawatts. Structural performance is evaluated for various arrangements of the carbon blade spar. Critical performance aspects of the carbon material and blade structure are discussed. To address the technical uncertainties identified, recommendations are made for new testing of composite coupons and blade sub-structure

Analysis of SNL/MSU/DOE fatigue database trends for wind turbine blade materials.

This report presents an analysis of trends in fatigue results from the Montana State University program on the fatigue of composite materials for wind turbine blades for the period 2005-2009. Test data can be found in the SNL/MSU/DOE Fatigue of Composite Materials Database which is updated annually. This is the fifth report in this series, which summarizes progress of the overall program since its inception in 1989. The primary thrust of this program has been research and testing of a broad range of structural laminate materials of interest to blade structures. The report is focused on current types of infused and prepreg blade materials, either processed in-house or by industry partners. Trends in static and fatigue performance are analyzed for a range of materials, geometries and loading conditions. Materials include: sixteen resins of three general types, five epoxy based paste adhesives, fifteen reinforcing fabrics including three fiber types, three prepregs, many laminate lay-ups and process variations. Significant differences in static and fatigue performance and delamination resistance are quantified for particular materials and process conditions. When blades do fail, the likely cause is fatigue in the structural detail areas or at major flaws. The program is focused strongly on these issues in addition to standard laminates. Structural detail tests allow evaluation of various blade materials options in the context of more realistic representations of blade structure than do the standard test methods. Types of structural details addressed in this report include ply drops used in thickness tapering, and adhesive joints, each tested over a range of fatigue loading conditions. Ply drop studies were in two areas: (1) a combined experimental and finite element study of basic ply drop delamination parameters for glass and carbon prepreg laminates, and (2) the development of a complex structured resin-infused coupon including ply drops, for comparison studies of various resins, fabrics and pry drop thicknesses. Adhesive joint tests using typical blade adhesives included both generic testing of materials parameters using a notched-lap-shear test geometry developed in this study, and also a series of simulated blade web joint geometries fabricated by an industry partner.

Blade System Design Studies Volume I: Composite Technologies for Large Wind Turbine Blades

As part of the U.S. Department of Energys Wind Partnerships for Advanced Component Technologies (WindPACT) program, Global Energy Concepts LLC (GEC) is performing a study concerning innovations in materials, processes and structural configurations for application to wind turbine blades in the multi-megawatt range. The project team for this work includes experts in all areas of wind turbine blade design, analysis, manufacture, and testing. Constraints to cost-effective scaling-up of the current commercial blade designs and manufacturing methods are identified, including self-gravity loads, transportation, and environmental considerations. A trade-off study is performed to evaluate the incremental changes in blade cost, weight, and stiffness for a wide range of composite materials, fabric types, and manufacturing processes. Fiberglass/carbon fiber hybrid blades are identified as having a promising combination of cost, weight, stiffness and fatigue resistance. Vacuum-assisted resin transfer molding, resin film infision, and pre-impregnated materials are identified as having benefits in reduced volatile emissions, higher fiber content, and improved laminate quality relative to the baseline wet lay-up process. Alternative structural designs are identified, including jointed configurations to facilitate transportation. Based on the results to date, recommendations are made for further evaluation and testing under this study to verify the predicted material and structural performance.

Concepts to Facilitate Very Large Blades.

Sandia National Laboratories (SNL) is developing concepts that will enable the utilization of longer blades that weigh less, are more efficient structurally and aerodynamically, and impart reduced loads to the system. Several of these concepts have been incorporated into subscale prototype blades. The description of these concepts and the results of prototype blade fabrication and testing are covered here.

Materials and Innovations for Large Blade Structures: Research Opportunities in Wind Energy Technology.

The significant growth in wind turbine installations in the past few years has fueled new scenarios that envision even larger expansion of U.S. wind electricity generation from the current 1.5% to 20% by 2030. Such goals are achievable and would reduce carbon dioxide emissions and energy dependency on foreign sources. In conjunction with such growth are the enhanced opportunities for manufacturers, developers, and researchers to participate in this renewable energy sector. Ongoing research activities at the National Renewable Energy Laboratory and Sandia National Laboratories will continue to contribute to these opportunities. This paper focuses on describing the current research efforts at Sandia’s wind energy department, which are primarily aimed at developing large rotors that are lighter, more reliable and produce more energy.

Introduction to NuMAD: A numerical manufacturing and design tool

Given the complex geometry of most wind turbine blades, structural modeling using the finite element method is generally performed using a unique model for each particular blade analysis. Development time (often considerable) spent creating a model for one blade may not aid in the development of a model for a different blade. In an effort to reduce model development time and increase the usability of advanced finite element analysis capabilities, a new software tool, NuMAD, is being developed.

CONCEPTS FOR ADAPTIVE WIND TURBINE BLADES

Bend-twist coupling in wind turbine blades has been shown to reduce both fatigue and extreme operating loads, especially when applied in conjunction with a pitch-controlled rotor. This type of coupling has been used in other industries, implemented either through biased lay-ups of fiber-reinforced materials, or with swept wings. The critical issues restricting the widespread implementation of this technology to wind turbines lies in the detailed design, manufacturing, and durability of the bend-twist-coupled blades. A series of industry contracts were initiated to evaluate/study these issues. The results of three of these studies are summarized in this paper. Global Energy Concepts (GEC) studied design issues from the perspective of traditional wind turbine blade conceptual design. Wichita State University investigated the use of braided composites with a multi-cellular blade structure. Finally, MDZ Consulting studied the possibilities of using sweep alone to achieve the desired bend-twist coupling. A common result of all the studies is that a higher stiffness fiber, such as carbon, has tremendous benefits in this application.Copyright

Investigating Aeroelastic Performance of Multi-MegaWatt Wind Turbine Rotors Using CFD

Recent trends in wind power technology are focusing on increasing power output through an increase in rotor diameter. As the rotor diameter increases, aeroelastic effects become increasingly important in the design of an efficient blade. A detailed understanding of the fluid elastic coupling can lead to improved designs; yielding more power, reduced maintenance, and ultimately leading to an overall reduction in the cost of electricity. In this work, a high fidelity Computational Fluid Dynamics (CFD) methodology is presented for performing fully coupled Fluid-Structure Interaction (FSI) simulations of wind turbine blades and rotors using a commercially available flow solver, AcuSolve. We demonstrate the technique using a 13.2 MW blade design.

Large Offshore Rotor Development: Design and Analysis of the Sandia 100-meter Wind Turbine Blade

Sandia National Laboratories’ (SNL) Wind & Water Power Technologies Department, as part of its ongoing R&D efforts, creates and evaluates innovative large blade concepts for horizontal axis wind turbines to promote designs that are more efficient aerodynamically, structurally, and economically. Recent work has focused on the development of a 100-meter blade for a 13.2 MW horizontal axis wind turbine, a blade that is significantly longer than the largest commercial blades of today (approximately 60 meters long). This paper summarizes the design development of the Sandia 100-meter All-glass Baseline Wind Turbine Blade, termed as “SNL100-00”, which employs conventional architecture and fiberglass-only composite materials. The paper provides a summary of performance margins from a series of analyses that demonstrate changes in various design drivers for large blade technology. Recommendations for improvements to large blade design and future research investment needs are discussed.

Innovative Design Approaches for Large Wind Turbine Blades

The primary goal of the WindPACT 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. The initial project task was to assess the fundamental physical and manufacturing issues that govern and constrain large blades and entails three basic elements: (1) a parametric scaling study to assess blade structure using current technology, (2) an economic study of the cost to manufacture, transport, and install large blades, and (3) identification of promising innovative design approaches that show potential for overcoming fundamental physical and manufacturing constraints. This report discusses several innovative design approaches and their potential for blade cost reduction. During this effort we reviewed methods for optimizing the blade cross-section to improve structural and manufacturing characteristics. We also analyzed and compared a number of composite materials and evaluated their relative merits for use in large wind turbine blades in the range from 30 meters to 70 meters. The results have been summarized in dimensional and non-dimensional format to aid in interpretation. These results build upon earlier parametric and blade cost studies, which were used as a guide for the innovative design approaches explored here.