Low frequency surge motion and inter-spacing distances between turbines in offshore wind farms

Floating offshore wind turbines offer a promising solution to global energy demands, harnessing wind resources in deep waters. Operational challenges arise from aerodynamic complexities induced by platform motions. Previous literature report large vortex ring wake structures for low frequency surge motions that can impact floating offshore wind farm design, particularly turbine spacing. This study aims at investigating the low frequency surge dynamics and vorticity dissipation with a focus on analysing inter-spacing distances between turbines. An Actuator Line Model is used based on Computational Fluid Dynamics using an OpenFOAM solver. The power and thrust of a downstream turbine at different downstream distances is explored. The results show that thrust and power oscillations on the downstream turbine can reach ±30% if a downstream inter-spacing distance of six diameters or less is used. This is consistent with earlier findings. This distance has been found to correspond to the dissipation of the large vortex ring structure resulting from the low frequency surge condition. The dissipation of vortex strength for the tip and root vortex has been characterised, leading to new insights for vortex based models. These conclusions provide guidelines for wind farm designers to ensure consideration of low frequency surge when establishing turbine spacing.