Wind tunnel investigation of the wake-flow response for a floating turbine subjected to surge motion

Floating wind turbines undergo large translation motions allowed by the high compliancy of the support structure. Large motions affect the rotor aerodynamic response and wake. This paper examines wake measurements of a wind tunnel experiment with a scale model of the DTU 10MW subjected to imposed harmonic surge motion. The effect of surge motion on the wake is detected by means of spectral analysis of velocity data. It is found that when the rotor undergoes surge motion, periodic forcing is introduced into the fluid, which produces a harmonic variation of the wake speed. The velocity perturbation around the rotor is then convected downstream at about the average axial velocity in the wake. The amplitude of the velocity pulsation at 2.3D is radially-dependent, and is correlated to the amplitude of the variation of the normal-force distribution along the blade.