Power and wake of a floating wind turbine in surge motion: Theoretical and experimental investigations

The deployment of floating offshore wind turbines (FOWTs) necessitates a thorough understanding of how platform motions influence turbine performance under atmospheric boundary layer (ABL) conditions. This study investigates the impact of surge motion on the power and wake characteristics of a model FOWT through integrated theoretical analyses and wind tunnel experiments in simulated ABL flow. Theoretically, we trace the effects from the blade element to the full rotor, developing a first-order analytical framework to interpret surge-induced aerodynamic responses and wake pulsations. Experimentally, we impose mild surge motions (Strouhal number S t = 0 –0.27) on a FOWT model in ABL flow and measure power output and wake velocity. For the mild prescribed surge conditions investigated, results show that surge motion directly induces periodic power fluctuations, with spectral peaks matching the surge frequency. Although the mean power remains largely unaffected, power fluctuations (RMS) increase by up to 230% relative to the fixed-bottom reference case. In the near wake, turbulence intensity increases by up to 200% near the wake centerline, whereas the far-wake mean velocity deficit changes by less than 5% at seven rotor diameters downstream. Surge motion also moderately modulates lateral wake meandering. Spectral analyses of the free-rotation response identify signatures of surge perturbations and turbulent fluctuations. The results indicate that the mean wake properties remain similar to those of a fixed-bottom turbine, supporting the applicability of existing fixed-bottom wake models within the investigated operating regime despite the notable effects on power fluctuations and near-wake turbulence.