Real-time hybrid model tests of a 17 MW ultra-large floating wind turbine using multi-rotor aerodynamic loading

To address the “Froude-Reynolds scaling conflict” and complex aero-hydro-servo coupling challenges of 17 MW Floating Offshore Wind Turbines (FOWTs), this study constructs and validates a 1:65 Real-Time Hybrid Model (RTHM) framework. It uses a customized AeroDyn substructure to calculate full-scale aerodynamic loads, physically mapping thrust and torque via a Multi-Degree-of-Freedom (MDF) multi-rotor loading device. The framework's fidelity was systematically evaluated through decay test, wind only, wave only, and combined wind-wave conditions. Benchmarked against OpenFAST simulations, the RTHM system achieved mean relative errors (MRE) for thrust and torque as low as 1.34% and 3.89% under rated conditions. Under severe combined wind-wave conditions, aerodynamic tracking errors remained within 9%, and statistical response errors for platform motions and mooring tensions were strictly bounded within 10%. Spectral analysis confirmed the capture of multi-scale dynamics, from low-frequency surge resonance to high-frequency 3P/6P/9P harmonics. Importantly, the physical tests captured the nonlinear reverse transfer of wave-frequency energy into the aerodynamic loads, verifying a bidirectional aero-hydrodynamic feedback loop. Furthermore, experiments revealed a more pronounced energy peak at the surge natural frequency than numerical simulations, highlighting traditional models' underestimation of low-frequency responses induced by second-order wave forces. This high-fidelity framework provides reliable experimental data for designing 17 MW ultra-large capacity wind turbines.