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Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research articles 06 Feb 2019

Research articles | 06 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Wind Energy Science (WES).

System-level design studies for large rotors

Daniel S. Zalkind1, Gavin K. Ananda2, Mayank Chetan3, Dana P. Martin4, Christopher J. Bay5, Kathryn E. Johnson4,5, Eric Loth6, D. Todd Griffith3, Michael S. Selig2, and Lucy Y. Pao1 Daniel S. Zalkind et al.
  • 1Department of Electrical, Computer & Energy Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
  • 2Department of Aerospace Engineering, University of Illinois Urbana-Champaign, Champaign, IL, USA
  • 3Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
  • 4Department of Electrical Engineering, Colorado School of Mines, Golden, CO 80401, USA
  • 5National Wind Technology Center, National Renewable Energy Laboratory, Golden, CO 80401, USA
  • 6Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA, USA

Abstract. 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.

Daniel S. Zalkind et al.
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Daniel S. Zalkind et al.
Daniel S. Zalkind et al.
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Publications Copernicus
Short summary
We present a model that both (1) reduces the computational effort involved in analyzing design trade-offs and (2) provides a qualitative understanding of the root cause of fatigue and extreme structural loads for wind turbine components from the blades to the tower base. We use this model in conjunction with design loads from high-fidelity simulations to analyze and compare the trade-offs between power capture and structural loading for large rotor concepts.
We present a model that both (1) reduces the computational effort involved in analyzing design...