BAR: Big Adaptive Rotor Project

BAR aims to maximize the advantages of large-scale land-based rotors and their potential for increased energy generation.

Now in its second phase, the project involves researchers from NREL and Sandia National Laboratories.

Colored lines swirling off the screen to the right

This visualization shows the wake behind a lightweight, slender, and highly flexible wind turbine rotor designed at NREL to simulate the next generation of land-based wind turbines. The wake was generated by running the aero-servo-elastic framework OpenFAST, its free-wake vortex model OLAF, and the geometrically exact beam model BeamDyn. Photo by Pietro Bortolotti, NREL


Designing the Rotor Blades for the Next Generation of Land-Based Wind Turbines

The past few decades have seen substantial reductions in the cost of wind energy. One key factor behind this trend has been the increase in average rotor size. Larger rotors capture more energy while limiting costs, such as operation and maintenance and balance of stations. Low-specific-power turbines—i.e., relatively larger rotors on the same machine rating—increase capacity factors and the availability of wind power.

The U.S. Department of Energy's BAR project conducts several investigations to support the land-based wind turbines of the future. Investigating innovations such as highly flexible blades, controlled bending of components during rail transportation, distributed aerodynamic control, and novel materials in manufacturing will simultaneously boost wind energy capture while limiting costs. To support these studies, the numerical tools are also improved, verified, and validated.

Project Outline

BAR Phase II pursues this mission by conducting work in three focus areas, which are represented by three tasks:

  • The first task aims to show the value and unresolved challenges of flexible blades and distributed aerodynamic control devices. Task 1 activities will be described in upcoming technical reports.
  • In the second task, NREL researchers are advancing the state of the art of numerical models that simulate wind turbines, both at the single turbine level and within a wind farm. Efforts are being dedicated to accurately model the complex deformations and the unsteady aerodynamic effects experienced by highly flexible blades. Work is conducted in the modules BeamDyn and AeroDyn15 of OpenFAST.
  • The third and last task conducts three experiments about aeroelastic stability of wind turbines, a downwind rotor experiment, and a structural experiment at coupon, subcomponent, and scaled blade levels. Task 3 also provides support to the project Rotor Aerodynamics, Aeroelastics and Wake. The ultimate goal of Task 3 is to provide validation data for the new suite of advanced engineering design tools developed within the BAR project.

Phase I: Coding Advances for Larger Land-Based Wind

To help clarify and better articulate the science and engineering hurdles facing potential turbine concepts, researchers have been extending the modeling capabilities of a variety of NREL's numerical tools. Improvements have been implemented in aeroservoelastic model OpenFAST, conceptual wind turbine design framework Wind-Plant-Integrated System Design and Engineering Model, turbine Reference OpenSource Controller, and the novel design framework Wind Energy with Integrated Servo-control. All these tools allow to model turbine performance and turbine system-level interactions.

BAR researchers have also developed cOnvecting LAgrangian Filaments, a new free-vortex wake module included in NREL's OpenFAST wind turbine simulation tool. The models the turbine wake using particles connected via filaments and is programmed to generate realistic representations of large, flexible turbine blades, providing users an alternative to traditional, lower-fidelity aerodynamic models. As an open-source, mid-fidelity tool, cOnvecting LAgrangian Filaments enables designers throughout the wind industry to more accurately and predictably model their own designs, reducing their development costs, while further developing the software collaboratively.

The BAR project funded improvements to detailed, cross-sectional analysis solver ANBA4 and composite blade mesh tool Structural Optimization and Aeroelastic Analysis. These two tools are under active development.

The BAR project started in 2018 and its first phase concluded in 2021. An NREL report summarizes all the key findings obtained during BAR Phase I.

Phase II: Maturing Technology Readiness for Large Wind Turbine Designs

BAR is now in Phase II, which focuses on the techno-economic assessment, detailed design, and experimental validation necessary to further mature the technology readiness level of very large, rail transportable, blade designs identified in BAR Phase I as promising technologies for the next-generation of land-based wind turbines.

The goals of BAR Phase II are to facilitate the early industry adoption of highly flexible, downwind, and distributed aerodynamic control technologies as well as to accelerate the deployment of land-based wind turbines. Most of the findings and the numerical models developed under BAR will be immediately transferable to the offshore wind applications and will support the development and deployment of tall tower and offshore turbine rotor technology in support of President Biden’s 2035 wind energy deployment goal.

Finally, BAR seeks strong collaborative engagement with industry stakeholders and holds quarterly meetings with an external advisory board formed of industry experts to collect feedback and disseminate results.

Bar Project Team


Co-Project Lead: Pietro Bortolotti

NREL research engineers include:

  • Mayank Chetan
  • Derek Slaughter
  • Emmanuel Branlard
  • Chris Ivanov
  • Andy Platt
  • Jason Jonkman
  • Jason Roadman
  • Scott Dana
  • Derek Berry
  • Scott Hughes.

Sandia National Laboratories

Co-Project Lead: Josh Paquette

Sandia National Laboratory research engineers include:

  • Evan Anderson
  • Ernesto Camarena
  • Chris Kelley.


Pietro Bortolotti

Researcher III, Mechanical Engineer