This study investigates the unsteady aerodynamic response, wake evolution, and
vortex dynamics of an ultra-large floating offshore wind turbine (FOWT) under
coupled motion–wave conditions. A high-fidelity aero–hydrodynamic CFD model is
employed for the IEA 22 MW reference turbine. Platform pitch and surge motions
are prescribed via sinusoidal functions, and wave conditions are independently
introduced by considering two representative sea states (H = 4 m and 7 m) and a
no-wave case. Results show that pitch and combined pitch–surge motions
significantly amplify unsteady aerodynamic effects, increasing peak power from
81.1 MW (P5S0) to 92.6 MW (P5S5), with periodic negative power output and severe
dynamic stall. Under strong motion, waves further raise peak power to 93.4 MW
(H7P5S5), indicating a coupled amplification effect. Dynamic stall is mainly
triggered by pitch motion, expanding in scope and duration with motion
amplitude; wave effects on stall remain limited. Platform motion also enhances
wake recovery by increasing inflow shear and turbulence, leading to higher
turbulent kinetic energy (TKE) and a reduced velocity deficit (ΔŪ). Waves
compress the low-speed wake core and reduce ΔŪ from 0.248 (no-wave case) to
0.204 under H7 conditions at x/D = 3.0, with the effect being particularly
evident under combined motion. Vortex visualization reveals that platform
movement leads to vortex merging, ring thickening, and deflection, with combined
motion creating the strongest mixing. Wave-generated vortices interact with tip
vortices near the surface, becoming more intense under larger wave heights. In
general, platform motion is the main factor in FOWT unsteady aerodynamics, while
waves have secondary but cooperative effects by changing inflow structures and
aiding wake recovery. This study offers theoretical support and engineering
guidance for aerodynamic design optimization and wind farm layout of
next-generation ultra-large floating offshore wind turbines.