Wake Steering for Wind Turbine Fatigue Load Optimisation

Wake steering is currently being implemented on commercial wind turbines to increase the power output from densely-packed wind farm layouts. Apart from increased power capture, wake steering also has an impact on the loads of both the upstream turbine due to operation in yawed inflow conditions, and on the downstream turbine due to reduction in the effective turbulence caused by the deflection of the wake. In this paper, commonly used wake expansion and wake deflection models are extended to obtain an analytical expression for the modified effective turbulence experienced by the downwind turbine. The impact of the modified yaw inflow and turbulence on wind turbine fatigue loads are investigated in a commercial aeroelastic environment. With partial overlap, significant changes in the effective turbulence and the loading of the downwind turbine can be observed. Wake steering strategies are hence recommended to consider both power and loads consequences in order to achieve the correct balance between turbine lifetime extension and short-term energy gains.