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.


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

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.

Why Rotor Instrumentation?

During a wind turbine’s operational lifetime, its rotor blades endure a wide variety of wind loading. The blades directly capture all of the force applied to the entire wind-turbine system.

A turbine’s exact wind loading is fundamental to overall system design. Due to the large potential for variability in
•atmospheric conditions,

•terrain topology, and

•turbine placement with respect to other turbines,

exact loading is difficult to model accurately. To overcome the wind-loading unknowns the structure will experience during its lifetime—to ensure that the unit operates to the end of its design/warrantied lifetime (usually 20 years)—additional safety factors are engineered into the design, usually requiring heavier and more costly components.

By implementing a set of sensors to measure wind-loading forces on the rotor blades during actual operation, we can shine light on the unknowns of how the wind acts directly on the wind-turbine system.

This work has been funded by the Department of Energy’s Wind and Water Power Program.
Fiber Gragg Grating sensors installation
Sandia staff installing Fiber Bragg Grating sensors in the roots of 13 m wind-turbine blades used at the Scaled Wind Farm Technology (SWiFT) facility.

Sensor Capabilities

Attaining a better understanding of the fundamental physics behind the loading that occurs during wind-turbine operation requires many different sensor types. Sandia engineers work with a wide array of transducers to characterize the surrounding environment as well as the turbines’ aerodynamic and structural responses. We measure

•atmospheric pressure, relative humidity, and temperature to determine local air density;

•incoming wind speed and direction with state-of-the-art sonic anemometers, as well as with International Electrotechnical Commission-standard calibrated cup anemometers and wind vanes;

•structural response on the turbine tower, including acceleration and strain, in order to determine rotor thrust loading—and detect any vibration that may be out of the ordinary;

•rotor-blade strain, acceleration, and surface pressure via sensors mounted on the rotor itself—in order to quantify direct loading during turbine operation from within the rotating reference frame.

SMART rotor
A SMART rotor with embedded sensors.

Recent Projects

The SMART active aerodynamics rotor was recently flown to assess the control authority of trailing edge flaps during operation. Many structural sensors monitored rotor loading to positively confirm the ability of the flaps to regulate blade wind loading.

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.
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).

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