A New Fatigue Analysis Procedure for Composite Wind Turbine Blades

Abstract

A fatigue analysis procedure including random wind field simulation, aerodynamic analysis, stress analysis by finite element analysis, and fatigue damage evaluation based on tested fatigue data has been developed for large horizontal axis wind turbine blades. In order to simulate realistic wind loads applied on the blade while maintaining affordable computation time, the sectional surface pressure fields obtained from XFOIL are modified to match the lift, drag, and moment coefficients obtained using NREL’s AeroDyn. Thus the modified pressure distribution includes the effect of the dynamic stall and the wake on the turbine rotor aerodynamics. A high-fidelity finite element blade model, which could easily tailor the design of composite materials in the blade, has been parameterized for the detailed stress analyses. Constant life diagrams based on the tested fatigue data have been constructed for fatigue damage evaluation under multi-axial complex stress states of variable amplitude. Starting from the random wind field simulation, the evaluated fatigue damage is determined by two random variables, 10-minute mean wind speed and 10-minute turbulence intensity factor. Consequently, the effect of mean wind speed and atmospheric turbulence toward blade fatigue can be investigated. The proposed fatigue analysis procedure can facilitate the reliability analysis and reliability-based design optimization of composite wind turbine blades considering wind load uncertainty.