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Research Papers

Comparing Three Aerodynamic Models for Predicting the Thrust and Power Characteristics of a Yawed Floating Wind Turbine Rotor

[+] Author and Article Information
Tonio Sant

Mem. ASME
Associate Professor
Department of Mechanical Engineering,
University of Malta,
Msida MSD 2080, Malta
e-mail: tonio.sant@um.edu.mt

Kurt Cuschieri

Department of Mechanical Engineering,
University of Malta,
Msida MSD 2080, Malta
e-mail: kurt.cuschieri.09@um.edu.mt

1Corresponding author.

Manuscript received July 30, 2015; final manuscript received January 8, 2016; published online February 23, 2016. Assoc. Editor: Yves Gagnon.

J. Sol. Energy Eng 138(3), 031004 (Feb 23, 2016) (12 pages) Paper No: SOL-15-1241; doi: 10.1115/1.4032684 History: Received July 30, 2015; Revised January 08, 2016

This study compares the time-varying rotor thrust and shaft power characteristics of a yawed floating offshore wind turbine (FOWT) predicted by three different open-source aerodynamic models. These models involve the blade-element-momentum (BEM) and the general dynamic wake (GDW) methods implemented in the design code fast developed by NREL, and a higher fidelity free-wake vortex model (FWVM) that is capable of modeling the unsteady skewed helical wake development of the yawed rotor. The study is based on the NREL 5 MW baseline rotor installed on the MIT tension-leg platform (TLP) operating with different rotor yaw angles and under regular sea wave conditions. Both the undisturbed wind speed and rotor speed are maintained constant throughout the analysis, though different sea wave heights and periods are considered. Initially, the motions of the FOWT under both axial and yawed rotor conditions are estimated in a time domain using fast. These motions are then prescribed to winds, an open-source FWVM developed by the University of Massachusetts Amherst, to determine the aerodynamic rotor thrust and power as a function of time. Both TLP surge and pitch motions are noted to impact the rotor thrust and power characteristics considerably. The three models have consistently shown that the TLP motion exhibits a negligible impact on the time-averaged rotor shaft thrust and power of the yawed rotor. On the other hand, the cyclic component of rotor thrust and power are found to be significantly influenced by the wave state at all yaw angles. Significant discrepancies between the predictions for this cyclic component from the three models are observed, suggesting the need of further research through experimental validation to ensure more reliable aerodynamics models are developed for floating wind turbine design software packages.

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Figures

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Fig. 1

Definition of rotor yaw angle and the 6DOFs for the floating system

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Fig. 3

Variation of thrust coefficient with yaw angle

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Fig. 4

Variation of power coefficient with yaw angle

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Fig. 5

Variation of thrust ratio with yaw angle

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Fig. 6

Variation of power ratio with yaw angle

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Fig. 7

fast predictions for mean surge position of TLP for regular waves of fixed height Hw equal to 3 m and varying period Tw

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Fig. 8

fast predictions for surge amplitude of TLP for regular waves of fixed height Hw equal to 3 m and varying period Tw

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Fig. 9

fast predictions for mean sway position of TLP for regular waves of fixed height Hw equal to 3 m and varying period Tw

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Fig. 10

fast predictions for amplitude of sway of TLP for regular waves of fixed height Hw equal to 3 m and varying period Tw

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Fig. 11

fast predictions for amplitude of the TLP pitch for regular waves of fixed wave period Tw equal to 9 s and varying height Hw

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Fig. 12

Peak-to-peak surge motions at the rotor hub height results from TLP surge and pitch motion. The phase difference between the surge and pitch motions is also indicated.

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Fig. 13

Variation of rotor thrust with time for Ψ = 15 deg and (Hw,Tw) = (3,12)

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Fig. 14

Variation of rotor shaft power with time for Ψ = 15 deg and (Hw,Tw) = (3,12)

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Fig. 15

Variation of rotor thrust ratio with wave period. Wave height is fixed.

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Fig. 16

Variation of rotor power ratio with wave period. Wave height is fixed.

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Fig. 17

Dependency of peak-to-peak variation in the rotor thrust and power on Hw at Ψ = 0 deg and 30 deg; Tw = 9 s

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Fig. 18

Dependency of peak-to-peak variation in the rotor thrust and power on Tw at Ψ = 0 deg and 30 deg; Hw = 3 m

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Fig. 19

Contribution of the TLP surge and pitch motions to the peak-to-peak deviation in the rotor thrust and power at different wave heights; Tw = 9 s

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Fig. 20

Contribution of the TLP surge and pitch motions to the peak-to-peak deviation in the rotor thrust and power at different wave periods; Hw = 3 m

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