Fatigue and extreme load reduction on two‐bladed wind turbines using the flexible hub connection

Abstract

The load reduction potential in regular operation and the design drivers of a flexible hub connection on two‐bladed turbines are presented in this paper. Developed for the two‐bladed Skywind 3.4 MW wind turbine, the flexible hub connection integrates an additional, multidirectional elasticity between the hub mount and the nacelle carrier to reduce the load transfer into the support structure. The stiffness and damping properties of the interface connection determine the load amplitudes of the system and influence the overall turbine dynamics. Consequently, the design relevant operating scenarios change due to a potential dynamic instability, resonance, or violation of deflection margins in comparison with a nonflexible hub connection. The system's capability to reduce fatigue and ultimate loads is assessed in several turbulent inflow conditions and transient operating states, while taking into account the operating limits of displacements. A permutation of the dynamic coupling parameters is conducted to characterize the sensitivity of load characteristics to the design variables. By identifying the critical operating conditions, it is possible to provide design guidelines for an effective optimization strategy.