Sandia’s Wind Energy Technology Department seeks opportunities to advance the current state of the art in rotor technology such that rotors can capture more energy, more reliably, with lower system loads – all at a lower end cost. The blades make up about 14% of the capital cost of a full turbine (Tegen, 2013), but they are responsible for practically 100% of the energy capture in a wind plant. They are responsible for all the steady and dynamic loads which drive the design and cost for the remainder of the turbine system – hub, shafts, bearings, gearbox, nacelle bedplate, tower and foundation. Research at Sandia has enabled the wind industry to provide competitively low cost of electricity using increasingly optimized systems.

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Wind turbine blade finite element model cross section showing regions of varied material layups.

Sandia rotor innovation activities fall into two categories:

  1. Use of simulation to evaluate rotor innovation concepts. Examples include the Sandia 100m blade design progression and the Sandia investigation of the effects of increasing maximum tip velocity on optimum rotor designs. Complete and accurate numerical design methods are critical to our work in this area. Projects result in public, detailed models and tools that are beneficial to the entire wind energy research community.
  2. Design, build, and test to validate rotor innovation concepts and to enable large experimental campaigns, such as the DOE Atmosphere-to-electrons (A2e) Initiative. This work leads to public field test data which is used to improve important simulation and analysis tools, enabling effective evaluation of future innovations.

Selected design studies:

External Reference

  • Tegen, S., Lantz, E., Hand, M., Maples, B., Smith, A., and Schwabe, P. “2011 Cost of Wind Energy Review,” National Renewable Energy Laboratory: NREL/TP-5000-56266, 2013.

Rotor Innovation Projects

Sandia uses CACTUS to predict three-dimensional visualization of flow velocities for the region downwind of an operating rotor.

Sandia uses CACTUS to predict three-dimensional visualization of flow velocities for the region downwind of an operating rotor.

Previous wind turbine rotors have used conventional airfoils and conventional design in which rotor design aims to attain maximum possible aerodynamic efficiency. Sandia has shown how non-conventional approaches may lead to far more effective wind turbine systems, seeking the balance between aerodynamic and structural efficiency. While flatback airfoils are not as aerodynamically efficient, they provide greater structural efficiency. Additionally, less-than-maximum aerodynamic efficiency rotor design may lead to overall lower loads, more effective wind turbine wakes, and increased wind farm output even at lower turbine loads.

Sandia uses high-efficiency numerical methods–such as Blade Element Momentum Theory (BEMT)–as well as high-fidelity numerical methods—such as vortex methods like CACTUS, Reduced Order Navier Stokes (RANS) and Large Eddy Simulation methods–to conduct innovative rotor design.

Recently, Sandia has begun to incorporate wake recovery characteristics into rotor design to enable rotors which may enable closer turbine spacing for more effective use of available land area.

Two-dimensional airfoil velocities created using Overflow

Two-dimensional airfoil velocities created using Overflow

Sandia staff working on installation of blade instrumentation for research activities

Sandia staff working on installation of blade instrumentation for research activities

Wind turbine blades capture all of the force applied to the entire wind-turbine system, and they endure a wide variety of wind loads during a turbine’s lifetime. Sandia has developed and fielded various sensors to directly or indirectly measure wind-load forces and structural dynamic response of the rotor in the field during operation in real-time. Measurements of rotor-blade strain, acceleration, and surface pressure via sensors mounted in the rotor are used to quantify direct loading during turbine operation.

Sandia has demonstrated many sensor technologies in flight tests of rotors in the past. The Sensor Blade 1 & 2 projects were focused efforts to learn about the most effective sensors for use on wind turbine rotors. Now, Sandia is set up for even more extensive sensor development and field-testing with the capabilities of SWiFT, which includes a large bank of GPS-synchronized data acquisition capabilities.

 

Sandia develops computer-aided engineering (CAE) tools with capabilities driven by the needs of current research projects. Rotor design is supported by a collection of tools which enable design and optimization of the rotor aerodynamics and structural performance. This unique and customizable toolset enables innovative designs and research on rotors, often including unconventional design objectives.

Numerical Manufacturing And Design Tool (NuMAD) is an example of a design tool we have developed to simplify the process of creating structural models and calculating blade properties for aero-elastic simulation. NuMAD is open-source and freely available for download.
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NuMAD© is a research code with capabilities that have been driven directly by Sandia/DOE research projects. The current version of NuMAD© (v2.0), released April 2013, may be obtained by returning the completed NuMAD Request form (as per instructions on the form).

The Sandia SMART rotor demonstrates active flow control combined with a suite of research-grade instrumentation.

The Sandia SMART rotor demonstrates active flow control combined with a suite of research-grade instrumentation.

The SMART active load control rotor was flown to assess control authority of trailing edge flaps during operation. Active flow and loads control is an exciting topic in wind energy research. It offers the potential to increase energy capture while reducing dynamic rotor loads through the use of advanced aero-structural feedback control. The Sandia demonstration gathered data which quantified the control authority of conventional trailing edge flaps for load control on the rotating, operating turbine. Data gathered was also used to assess current numerical models for prediction of active load control for wind turbines. Future projects will seek to quantify tradeoffs for various types of non-conventional flow control technologies as well as various types of closed-loop control of these technologies.