Wind tunnel investigation of the dynamic aerodynamic behaviors of floating wind turbines under surge motion

Floating offshore wind turbines (FOWTs) experience six degrees of freedom motion under the coupled action of wind, waves, and currents, among which surge motion has a particularly significant impact on their aerodynamic behaviors. Surge motion leads to dynamic changes in the relative inflow velocity. This leads to unsteady aerodynamics, affecting safety and efficiency. However, the aerodynamic mechanisms—especially rotor–tip vortex interactions—remain poorly understood due to the lack of experimental data. To address this gap, this study conducts wind tunnel model tests to investigate the unsteady aerodynamic characteristics of FOWTs under surge motion. A synchronized system captures inflow, blade pressure, and wake flow in real time, enabling simultaneous measurement of key aerodynamic parameters for comprehensive analysis. The results show that surge motion increases the average power output, reduces the average thrust, and amplifies fatigue loads. Additionally, the power coefficient exhibits a pronounced hysteresis effect with respect to variations in the relative tip speed ratio (TSR). Coupled analysis of rotor loads, blade pressure distribution, tip vortex dynamics, induced velocity, and effective angle of attack reveals that surge motion induces periodic stretching and compression of tip vortices. These vortex deformations dynamically alter the axial induction field, leading to cyclic fluctuations in the effective angle of attack and consequently influencing both power output and aerodynamic loads. This coupling mechanism causes notable dynamic discrepancies in thrust coefficient, power coefficient, and sectional aerodynamic loads even at identical relative TSRs. The newly revealed mechanism can be applied to the development of novel dynamic models for FOWTs.