Publications

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This document serves both as a guide and a record for requirements management associated with design of retrofit rotors for the Sandia SWiFT turbines. The rotors will support a long-term experimental campaign. Data gathered during the campaign will support formal verification and validation of complex flow numerical models for prediction of metrics deemed important for wind energy plant efficiency. These integrated projects involve multiple years of effort, dozens of engineers and collaborators, and dozens of stakeholders in the form of the research community, National Lab staff, and DOE staff. Creating of formal, written requirements will ensure flow-down of activities from high-level goals, aid communication, and enable clear verification of activities. A custom requirements schema is created and described. Commercial requirements management software —IBM Rational DOORS—is used to organize the information and ensure traceability. This document serves as a record of the process as well as a record of the exported, detailed contents of the DOORS database.

The total energy produced by a wind farm depends on the complex interaction of many wind turbines operating in proximity with the turbulent atmosphere. Sometimes, the unsteady forces associated with wind negatively influence power production, causing damage and increasing the cost of producing energy associated with wind power. Wakes and the motion of air generated by rotating blades need to be better understood. Predicting wakes and other wind forces could lead to more effective wind turbine designs and farm layouts, thereby reducing the cost of energy, allowing the United States to increase the installed capacity of wind energy. The Wind Energy Technologies Department at Sandia has collaborated with the University of Minnesota to simulate the interaction of multiple wind turbines. By combining the validated, large-eddy simulation code with Sandia’s HPC capability, this consortium has improved its ability to predict unsteady forces and the electrical power generated by an array of wind turbines. The array of wind turbines simulated were specifically those at the Sandia Scaled Wind Farm Testbed (SWiFT) site which aided the design of new wind turbine blades being manufactured as part of the National Rotor Testbed project with the Department of Energy.

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New blade designs are planned to support future research campaigns at the SWiFT facility in Lubbock, Texas. The sub-scale blades will reproduce specific aerodynamic characteristics of utility-scale rotors. Reynolds numbers for megawatt-, utility-scale rotors are generally vary from 2-8 million. The thickness of inboard airfoils for these large rotors are typically as high as 35-40%. The thickness and the proximity to three-dimensional flow of these airfoils present design and analysis challenges, even at the full scale, but more than a decade of experience with the airfoils in numerical simulation, in the wind tunnel, and in the field has generated confidence in their performance. When used on a sub-scale rotor, Reynolds number regimes are significantly lower for the inboard blade, ranging from 0.7 to 1 million. Performance of the thick airfoils in this regime is uncertain because of the lack of wind tunnel data and the inherent challenge associated with associated numerical simulations. This report documents efforts to determine the most capable analysis tools to support these simulations and to improve understanding of the aerodynamic properties of thick airfoils in this Reynolds number regime. Numerical results from various codes of four airfoils are verified against previously published wind tunnel results where data at those Reynolds numbers are available. Results are then computed for other Reynolds numbers of interest.

In this paper, the effect of two different turbine blade designs on the wake characteristics was investigated using large-eddy simulation with an actuator line model. For the two different designs, the total axial load is nearly the same but the spanwise (radial) distributions are different. The one with higher load near the blade tip is denoted as Design A; the other is Design B. From the computed results, we observed that the velocity deficit from Design B is higher than that from Design A. The intensity of turbulence kinetic energy in the far wake is also higher for Design B. The effect of blade load distribution on the wind turbine axial and tangential induction factors was also investigated.

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This report serves as documentation of the information and considerations involved in creation of the latest version of the SWIFT turbines aeroelastic model. Information used to create the model came from a variety of sources including original Vestas drawings and hardware characterization during construction of turbines at the site. Much of the original Vestas drawings remain proprietary and are not available to the public, though they have been referenced and included in the bibliography. The tower and blades of the turbine model were first created using available design information and then were calibrated to match experimental characterizations performed during construction. Some model inputs, such as airfoil polar data and estimated blade material properties, were computed. A basic controller is created to represent the basic operation of the modified SWiFT turbines.

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A reduction in cost of energy from wind is anticipated when maximum allowable tip velocity is allowed to increase. Rotor torque decreases as tip velocity increases and rotor size and power rating are held constant. Reduction in rotor torque yields a lighter weight gearbox, a decrease in the turbine cost, and an increase in the capacity for the turbine to deliver cost competitive electricity. The high speed rotor incurs costs attributable to rotor aero-acoustics and system loads. The increased loads of high speed rotors drive the sizing and cost of other components in the system. Rotor, drivetrain, and tower designs at 80 m/s maximum tip velocity and 100 m/s maximum tip velocity are created to quantify these effects. Component costs, annualized energy production, and cost of energy are computed for each design to quantify the change in overall cost of energy resulting from the increase in turbine tip velocity. High fidelity physics based models rather than cost and scaling models are used to perform the work. Results provide a quantitative assessment of anticipated costs and benefits for high speed rotors. Finally, important lessons regarding full system optimization of wind turbines are documented.

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Sandia is designing a set of modern, research-quality blades for use on the V27 turbines at the DOE/SNL SWiFT site at Texas Tech University in Lubbock, Texas. The new blades will replace OEM blades and will be a publicly available resource for subscale rotor research. Features of the new blades do not represent the optimal design for a V27 rotor, but are determined by aeroelastic scaling of relevant parameters and design drivers from a representative megawatt-scale rotor. Scaling parameters and design drivers are chosen based two factors: 1) retrofit to the existing SWiFT turbines and 2) replicate rotor loads and wake formation of a utility scale turbine to support turbine -turbine interaction research at multiple scales. The blades are expected to provide a publicly available baseline blade design which will enable increased participation in future blade research as well as accelerated hardware manufacture and test for demonstration of innovation. This paper discusses aeroelastic scaling approaches, a rotor design process and a summary of design concepts.

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This report documents the design, fabrication, and testing of the SMART Rotor. This work established hypothetical approaches for integrating active aerodynamic devices (AADs) into the wind turbine structure and controllers.