System-Level Design Studies for Large Rotors

Christopher Bay, Kathryn Johnson, Daniel Zalkind, Gavin Ananda, Mayank Chetan, Dana Martin, Eric Loth, D. Griffith, Michael Selig, Lucy Pao

Research output: Contribution to journalArticle

29 Scopus Citations


We examine the effect of rotor design choices on the power capture and structural loading of each major wind turbine component. A steady-state, harmonic model derived from simulations using the NREL aeroelastic code FAST is developed to reduce computational expense while evaluating design trade-offs for rotors with radii greater than 100 m. Design studies are performed, which focus on blade aerodynamic and structural parameters as well as different hub configurations and nacelle placements atop the tower. The effects of tower design and closed-loop control are also analyzed. Design loads are calculated according to the IEC design standards and used to calibrate the harmonic model and quantify uncertainty. Our design studies highlight both industry trends and innovative designs: we progress from a conventional, upwind, 3-bladed rotor, to a rotor with longer, more slender blades that is downwind and 2-bladed. For a 13 MW design, we show that increasing the blade length by 25 m while decreasing the induction factor of the rotor increases annual energy capture by 11% while constraining peak blade loads. A downwind, 2-bladed rotor design is analyzed, with a focus on its ability to reduce peak blade loads by 10% per 5 deg. of cone angle, and also reduce total blade mass. However, when compared to conventional, 3-bladed, upwind designs, the peak main bearing load of the up-scaled, downwind, 2-bladed rotor is increased by 280%. Optimized teeter configurations and individual pitch control can reduce non-rotating damage equivalent loads by 45% and 22%, respectively, compared with fixed-hub designs.
Original languageAmerican English
Number of pages35
JournalWind Energy Science Discussions
StatePublished - 2019

Bibliographical note

See NREL/JA-5000-75419 for final paper as published in Wind Energy Science

NREL Publication Number

  • NREL/JA-5000-73826


  • systems engineering
  • wind turbine design


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