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.
Comparing Three Aerodynamic Models for Predicting the Thrust and Power Characteristics of a Yawed Floating Wind Turbine Rotor
Manuscript received July 30, 2015; final manuscript received January 8, 2016; published online February 23, 2016. Assoc. Editor: Yves Gagnon.
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Sant, T., and Cuschieri, K. (February 23, 2016). "Comparing Three Aerodynamic Models for Predicting the Thrust and Power Characteristics of a Yawed Floating Wind Turbine Rotor." ASME. J. Sol. Energy Eng. June 2016; 138(3): 031004. https://doi.org/10.1115/1.4032684
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