OC6 Project Phase III: Validation of the Aerodynamic Loading on a Wind Turbine Rotor Undergoing Large Motion Caused by a Floating Support Structure
Authors: Bergua Roger , Robertson Amy , Jonkman Jason , Branlard Emmanuel , Fontanella Alessandro , Belloli Marco , Schito Paolo , Zasso Alberto , Persico Giacomo , Sanvito Andrea , Amet Ervin , Brun Cédric , Campaña-Alonso Guillén , Martín-San-Román Raquel , Cai Ruolin , Cai Jifeng , Qian Quan , Maoshi Wen , Beardsell Alec , Pirrung Georg , Ramos-García Néstor , Shi Wei , Fu Jie , Corniglion Rémi , Lovera Anaïs , Galván Josean , Nygaard Tor Anders , dos Santos Carlos Renan , Gilbert Philippe , Joulin Pierre-Antoine , Blondel Frédéric , Frickel Eelco , Chen Peng , Hu Zhiqiang , Boisard Ronan , Yilmazlar Kutay , Croce Alessandro , Harnois Violette , Zhang Lijun , Li Ye , Aristondo Ander , Mendikoa Alonso Iñigo , Mancini Simone , Boorsma Koen , Savenije Feike , Marten David , Soto-Valle Rodrigo , Schulz Christian , Netzband Stefan , Bianchini Alessandro , Papi Francesco , Cioni Stefano , Trubat Pau , Alarcon Daniel , Molins Climent , Cormier Marion , Brüker Konstantin , Lutz Thorsten , Xiao Qing , Deng Zhongsheng , Haudin Florence , Goveas Akhilesh 
Published: August 2022

Abstract. This paper provides a summary of the work done within Phase III of the Offshore Code Comparison, Collaboration, Continued, with Correlation and unCertainty project (OC6), under International Energy Agency Wind Task 30. This phase focused on validating the aerodynamic loading on a wind turbine rotor undergoing large motion caused by a floating support structure. Numerical models of the Danish Technical University 10-MW reference wind turbine were validated using measurement data from a 1:75 scale test performed during the UNsteady Aerodynamics for FLOating Wind (UNAFLOW) project and a follow-on experimental campaign, both performed at the Politecnico di Milano wind tunnel. Validation of the models was performed by comparing the loads for steady (fixed platform) and unsteady wind conditions (harmonic motion of the platform). For the unsteady wind conditions, the platform was forced to oscillate in the surge and pitch directions under several frequencies and amplitudes. These oscillations result in a wind variation that impacts the rotor loads (e.g., thrust and torque). For the conditions studied in these tests, the system mainly described a quasi-steady aerodynamic behavior. Only a small hysteresis in airfoil performance undergoing angle of attack variations in attached flow was observed. During the experiments, the rotor speed and blade pitch angle were held constant. However, in real wind turbine operating conditions, the surge and pitch variations would result in rotor speed variations and/or blade pitch actuations depending on the wind turbine controller region that the system is operating. Additional simulations with these control parameters were conducted to verify the fidelity between different models. Participant results showed in general a good agreement with the experimental measurements and the need to account for dynamic inflow when there are changes in the flow conditions due to the rotor speed variations or blade pitch actuations in response to surge and pitch motion. Numerical models not accounting for dynamic inflow effects predicted rotor loads that were 9 % lower in amplitude during rotor speed variations and 18 % higher in amplitude during blade pitch actuations.