Stochastic flutter of wind turbine blades under turbulence and load perturbations: Implications on offshore wind energy

The current trend in offshore wind energy is to design and install blades with larger swept areas that yield unprecedented efficiency. Long and slender blades are needed to achieve this objective. As a result of aerodynamic and structural tailoring, the blades are sensitive to various dynamic instability phenomena during standard operations. Among these phenomena, coupled flap-wise bending and torsion flutter may lead either to structural failure or system breakdown.

The author has been examining blade flutter under the influence of stochastic perturbations, which include both flow turbulence and aeroelastic load variability. A reduced-order Markov model has been used to describe the effects of the various perturbations. Mean-square stability has been considered. Numerical results suggest that perturbations may negatively impact the flutter angular speed and increase the risk of a failure.

In this study the model is employed to investigate moment stability beyond mean squares. Since the dynamic instability involves nonlinear propagation of the perturbations, flutter may exhibit amplitude dependency. Therefore, third-moment stochastic instability is thoroughly investigated. Stability of a reference wind turbine blade is examined. Results are also compared against preliminary simulations presented at the “9th International Colloquium on Bluff Body Aerodynamics and Applications”.