Aero‐structural dynamics of a flexible hub connection for load reduction on two‐bladed wind turbines

Abstract

In this study, an innovative concept for load reduction on the two-bladed Skywind 3.4 MW prototype is presented. The load reduction system consists of a flexible coupling between the hub mount, carrying the drive train components including the hub assembly, and a nacelle carrier supported by the yaw bearing. This paper intends to assess the impact of introducing a flexible hub connection on the system dynamics and the aero-elastic response to aerodynamic load imbalances. In order to limit the rotational joint motion, a cardanic spring-damper element is introduced between the hub mount and the nacelle carrier flange, which affects the system response and the loads. A parameter variation of the stiffness and damping of the connecting spring-damper element has been performed in the multi-body simulation solver Simpack. A deterministic, vertically sheared wind field is applied to induce a periodic aerodynamic imbalance on the rotor. The aero-structural load reduction mechanisms of the coupled system are thereby identified. It is shown that the fatigue loads on the blades and the turbine support structure are reduced significantly. For a very low structural coupling, however, the corresponding rotational deflections of the hub mount exceed the design limit of operation. The analysis of the interaction between the hub mount motion and the blade aerodynamics in a transient inflow environment indicates a reduction of the angle of attack amplitudes and the corresponding fluctuations of the blade loading. Hence, it can be concluded that load reduction is achieved by a combination of reduced structural coupling and a mitigation of aerodynamic load imbalances.

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

“…Several studies and publications are available about the aerodynamic modeling aspects, the aero‐structural response, and the load reduction mechanisms as well as fundamental stability issues of the flexible hub connection . The dynamic response of the hub mount is influenced by the design of the interface between the hub mount and the nacelle carrier, which is assumed to act as a linear rotational spring‐damper element.…”

“…The oscillation amplitude is increased for the softer configuration, and the peaks are retarded with respect to the stiffer setup. It was shown in Luhmann et al that the peak retardation along with higher oscillation amplitudes has a beneficial impact on the aerodynamic load imbalances acting on the rotor.…”

Aero-elastic analysis of wind turbines under turbulent inflow conditions

“…The multi-body dynamics (MBD) simulation code SIMPACK is used to simulate the structural dynamics of the turbine (as in Jassmann et al (2014) and Luhmann et al (2017)). The structural properties of the entire turbine have been modeled starting https://doi.org/10.5194/wes-2020-22 Preprint.…”

Advanced computational fluid dynamics (CFD)–multi-body simulation (MBS) coupling to assess low-frequency emissions from wind turbines

“…Volume sources generated by free-flow turbulence are neglected, which is justified for low Mach number flow because quadrupole volume noise is proportional to Ma 7 . This approach was validated for a rod-cylinder configuration and an airfoil in turbulent flow (Lutz et al, 2015;Illg et al, 2015). The acoustic monopole and dipole contributions to the observer sound pressure level (SPL) are computed by means of the FW-H equation.…”