Program Activities: Advanced Concepts, Analysis, and Design Tools

Blades are the only wind turbine component designed and manufactured uniquely for wind energy applications. The challenge is to create the scientific knowledge base and engineering tools to enable designers to maximize performance at the lowest possible cost. Activities at Sandia seek to produce research results, tools, and prototype evaluations necessary for the successful implementation of advanced design concepts into large innovative utility-grade blade designs. By focusing on improvements in blade technology through improved materials and manufacturing, optimized sensors, improved aerodynamic and structural codes, and enlarged rotors made possible by adaptive techniques, Sandia is providing innovative solutions to the industry.

Materials and Manufacturing

Wind turbine blades constitute a significant portion of the cost of a modern, utility-scale, wind turbine. These blades are comprised of relatively low-cost composite materials and current manufacturing processes are very labor-intensive. To facilitate the incorporation of larger blade designs into new turbines, Sandia studies composite materials and manufacturing processes targeted at developing innovations that will help reduce the nonlinear growth in blade weight. The objective of this effort is to provide innovations in materials, manufacturing processes, and embedded sensor technologies.

Sensors

The next generation of wind turbines will require the increased use of sensors for advanced control strategies and structural health monitoring in order to optimize system performance. There has also been an increased demand for diagnostic tools, such as Non-Destructive Inspection (NDI) systems (which are sensor systems), on the manufacturing floor to improve wind turbine blade quality. The Sensor Task has these two major goals:

• Provides a comprehensive set of NDI tools, and the accompanying expertise, to requestors in the wind industry.
• Identify promising sensing technologies and develop Commercial Off-The-Shelf (COTS) sensing systems for the wind industry.
• Engage with and communicate to the wind industry, in an open forum or under exclusiveness, knowledge and experience obtained under this task.
• Develop in-house expertise in the application of sensing systems to enable advanced wind turbine control and monitoring applications.
• The Sandia sensor effort:
• Identifies and researches promising sensing technologies and develop the expertise to reliably incorporate, operate and maintain these sensing technologies in wind turbine applications.
• Exercises sensing systems, as diagnostic tools, during wind turbine tests to help validate computer models and/or component designs.
• Leverages the sensing and NDI expertise available in-house at Sandia Labs, for wind industry applications inside and outside the national labs.
• Provides a collaborative environment in the development of Commercial Off-The-Shelf (COTS) sensing systems.

Advanced Manufacturing Initiatives (AMI)

Wind turbine blades constitute a significant portion of the cost of a modern, utility-scale, wind turbine. These blades are comprised of relatively low-cost composite materials and current manufacturing processes are very labor-intensive. Due to this high labor requirement for current blade manufacturing, there is a strong economic incentive to fabricate blades in low cost-of-labor countries rather than in the U.S. In addition to manufacturing costs, transportation costs for these large blades are also significant. Obviously, a U.S.-manufactured blade should have a decided transportation cost advantage over a blade made on a different continent. The goal of this research effort is to make the manufacturing cost difference between a U.S.-manufactured blade and an overseas blade less than the transportation cost difference for the same two blades for the U.S. wind energy market.

Innovative Concepts

Reduction of the wind-induced fatigue loading on wind turbine blades can lead to lighter and lower-cost blades and thus, lower wind cost of energy. One way to accomplish this reduction is by utilizing small aerodynamic load control devices on the blade trailing edge (similar to but smaller than flaps on an airplane wing) that can respond quickly to changes in wind speed and/or direction to attenuate the resultant blade fatigue loading. These control devices must be embedded in the blade and integrated with sensors that determine the local flow condition at any point on the blade, actuators to deploy or retract the devices, and an appropriate dedicated control system to control when the devices should be deployed or retracted. Sandia has developed a suite of modeling tools to enable investigation of three primary areas of interest for this technology:

• Analysis of the aerodynamic performance of potential load control device configurations (some of these configurations are shown in the figure to the right).
• Development of control systems for deploying and retracting these load control devices.
• Calculation of the impact of these devices on the fatigue damage at critical points on the turbine.

These tools are being utilized to study the use of various load control devices on wind turbines ranging in size from 600kW to 13MW+. Enhancements to these tools will incorporate some of the developments from the Aerodynamic Tools and Aeroacoustics task and the Design Tools and System Modeling task to improve tool physical fidelity and increase the spatial resolution of the models that can be analyzed. Wind tunnel testing and field testing will be used to validate selected simulation results. In addition, advanced control systems will be developed to optimize the performance of a wind turbine that incorporates multiple technologies for mitigating blade fatigue damage (both independent blade pitch control and active aerodynamic load control, for example). Additional work will focus on continued development the advanced sensor technology needed to determine the local wind-induced loading at any point on the blade.

Aerodynamic Tools and Aeroacoustics

Accurate prediction of aerodynamic loads on wind turbine blades is an essential component of the blade design and analysis process. Sandia is leveraging the high performance computing resources of the laboratory to bring Computational Fluid Dynamics (CFD) methods to bear on blade and rotor analysis. CFD is also being used to characterize the aerodynamic performance of active aerodynamic control devices, including a morphing blade trailing edge, and to investigate the aerodynamic and noise characteristics of structurally efficient airfoils that have a blunt trailing edge. Sandia is currently building capability to perform coupled structural dynamics/CFD analysis in order to provide high-fidelity aero-elastic load predictions and to investigate wind turbine aero-elastic stability.
Aeroacoustic noise sources from a wind turbine not only often dominate over other turbine noise sources, they also often limit the tip speed of the rotor, thereby increasing the required torque for a given amount of power. Drive train components are sized based on torque, so that if torque can be reduced the overall cost of the turbine can also be reduced. Aero-acoustic sources, particularly near the blade tips, are poorly understood and current design decisions are based on prior experience and trial-and-error methods. Sandia is actively developing computational noise prediction capability in order to increase understanding of blade aeroacoustics and enable quieter blade designs. In tandem with this modeling effort, Sandia is engaged with the National Renewable Energy Laboratory to develop and apply advanced acoustic measurement techniques for field measurements of aeroacoustic noise. These measurements will be used to investigate noise mitigation approaches and to validate the computational prediction tools.

Design Tools and System Modeling

Sandia will continue its efforts to develop computational tools to significantly improve the structural and aeroelastic analysis capability available to the wind industry. These analytical capabilities may be used to guide the design of new blades as well as to verify/improve the design of existing blades. The validity of the tools will be demonstrated by continuing a comprehensive design, analysis, build, test, and validation program. A major focus is being placed on better integration of the structural analysis and aeroelastic codes. This effort will result in a reduction in design time and lead to better and more efficient designs for future wind turbine hardware.