Integrating variable wind load, aerodynamic, and structural analyses towards accurate fatigue life prediction in composite wind turbine blades

A comprehensive fatigue analysis framework for composite wind turbine blades has been developed. It includes variable wind loads from wind field simulation and aerodynamic analysis, stress prediction by finite element analysis, and fatigue damage evaluation based on the resulting fatigue data. The variable wind load is represented by a joint distribution of mean wind speed and turbulence intensity. In order to simulate realistic wind loads applied on the blade while maintaining affordable computational time, the sectional surface pressure fields obtained from the potential flow aerodynamics model XFOIL are transformed to match the lift, drag, and moment coefficients obtained using AeroDyn. Thus, the modified pressure distribution includes the effect of dynamic stall, rotation, and wake effects on the blade aerodynamics. A high-fidelity finite element blade model, in which the design of composite materials can be easily tailored, has been parameterized for detailed stress analysis. The non-proportional multi-axial complex stress states are involved when calculating 10-min fatigue damage of section points through laminate thickness. The annual fatigue damage is calculated based on the 10-min fatigue damage and the joint distribution of 10-min mean wind speed and 10-min turbulence intensity. Consequently, the blade fatigue effect due to not only the mean wind speed and the atmospheric turbulence in the short term, but also the wind load variation in a large spatiotemporal range, can be investigated. The developed fatigue analysis framework can facilitate reliability analysis and reliability-based design optimization of composite wind turbine blades.