Fatigue degradation of wind turbines considering dynamic wake meandering effects

This paper systematically investigates the effects of six factors, namely wind shear, ambient turbulence, wake meandering, wake-added turbulence, turbulence intensities, and wind speed, on the dynamic responses and fatigue degradation of wind turbines in the wake region. An improved mid-fidelity code, FAST.Farm, is used, which considers wake-added turbulence by adopting an additional wind domain with the Mann model. Different distributions of short-term damage equivalent stresses are found in two selected components, namely figure-8 and elliptical distributions, respectively, for nonturbulent and turbulent inflows at the blade root and a consistent infinity-distribution at the tower section for different inflows. An apparent lifetime reduction is observed at the blade root and tower base after the introduction of ambient turbulence, wake meandering, and wake-added turbulence. This lifetime reduction is more critical at the tower bases of downstream wind turbines, where the fatigue lifetime can be shorter than the designed service lifetime (20 years) owing to the wake effect. Considering a Rayleigh distribution with an average wind speed of 8.5 m/s, the fatigue lifetimes of turbines located 4D and 8D downstream of another turbine are approximately 45.86 % and 13.12 %, respectively, lower than the fatigue lifetime of the upstream turbine, whereas the reductions are 38.80 % and 5.03 %, respectively, for an average wind speed of 10.0 m/s. Given that the wake effect on the fatigue lifetime has already been highlighted in recent design standards, the findings of the present study are expected to provide guidance for fatigue evaluation in practice, which will help improve fatigue estimations, extend turbine lifetimes, and reduce the construction costs.