Floating wind turbine motions signature in the far-wake spectral content – A wind tunnel experiment

Abstract. The growing interest in floating offshore wind turbines (FOWTs) is rooted in the potential source for increased offshore energy production. As the technology is still in a pre-industrial state, several questions remain to be addressed where little field data is available. This study uses physical modelling at a reduced scale to investigate the signature of the floating motions into the wake spectral content of a simplified FOWT model. A wind turbine model based on the actuator disc concept is placed in an atmospheric boundary layer wind tunnel and subjected to a range of surge, heave and pitch motions. The signatures of idealised sinusoidal motion and realistic broad-band motion on the model’s wake at distance of 4.6 D (D being the disc diameter) and 8 D are measured through the use of a rake of single hot-wires. The spectral analysis shows that harmonic motion leaves to clear signatures in the far-wake's energy spectra, mainly in the top tip region, while broad-band motion does not leave easily detectable signatures.