Steady-state evaluation of fatigue loads for the helix wake-mixing control method

Wake-mixing strategies offer promising opportunities to increase 
wind farm power production, but their impact on structural fatigue loading 
remains insufficiently understood. This study evaluates the helix wake-mixing 
method by jointly assessing power gains and fatigue loads at the wind-farm 
scale. A steady-state helix wake model is coupled to a data-driven load surrogate 
model. The surrogate model was trained on aeroelastic simulations using inflow 
slices generated by large-eddy simulations and predicts damage equivalent 
loads based on sector-averaged wind speed and turbulence intensity. The 
coupled framework is first evaluated on a two-turbine array, considering varying 
helix pitch amplitudes and wake overlap. The model captures the trends 
observed when coupling the surrogate model to large-eddy simulation inflow, 
showing increased fatigue loads on both upstream and downstream turbines. 
The framework is subsequently applied to a 69-turbine offshore wind farm case 
study. Farm-wide optimization of the helix method at below-rated wind speeds 
yields an increase of up to 1.1 % in annual energy production, accompanied by 
increased fatigue loading across all evaluated components. The largest 
increases are observed for the pitch bearings, while tower base loads are less 
affected.