Effects of coupled platform motions on the aerodynamic performance and wake characteristics of a floating horizontal-axis wind turbine

The aerodynamics of floating horizontal-axis wind turbines (FHAWTs) are complex due to platform motions in real sea states. The impacts of coupled platform motions on the aerodynamic loads, wake structure, and wake recovery of FHAWTs were investigated through computational fluid dynamics simulations. Results show that the increases in the maximum rotor power of FHAWTs (compared with the fixed-base ones) under sinusoidal pitch-surge motions (3892 kW) were close to the sum of those under pitch (2121 kW) and surge (1622 kW) motions. The wake tilt angles under pitch-surge motions agreed with those under pitch motions, causing similar wake recovery. The increase in wave periods (T_w) amplified the resonance between waves and platforms under the wind-wave coupling, increasing the maximum rotor power and thrust. Compared with T_w = 16 s, the relative decreases in the averaged wake velocity, which was 7D (where D is the rotor diameter) downwind of the FHAWTs, were 5.93% and 2.64% at T_w = 8 s and 12 s, respectively. Long T_w increased pitch periods, yielding fast wake recovery by enhancing the interaction between blade-tip vortices and hub ones. The output power of a floating wind farm was higher than the fixed-base counterpart due to fast wake recovery.