Introduction Aeroelasticity

Design process

Aeroelastic analysis plays an important role during the design of a wind turbine.

When looking at the ECN software currently available for the design process, during the first design phase it is advised to investigate the aeroelastic stability of the turbine quickly using Bladmode. This program will give the damping values for several modes at different wind speeds in just a few seconds. It however does take into account a detailed blade model where among other a structural pitch angle and a position of the elastic axis along the radial distance of the blade can be included in the model. The importance of including a detail such as the distribution of the structural pitch angle is illustrated in the figure.

Results obtained using Bladmode: damping of first coll. edgewise mode for a blade model with distributed structural pitch (red) compared to models with one structural pitch angle at the root of the blade.

Once the first phase of the design is finalised a more thorough check using Turbu would be a possible next step. In Turbu the model of the turbine is more complete than in Bladmode. The analysis does also run rather quickly.

The load set calculations can then be performed using PHATAS.

Developments

The current state-of-the art in aeroelastic analysis for wind turbines needs further improvement to obtain a better reliability. Improvements are needed for simulations concerning oblique inflow, individual pitch, large deformations and complex drive train and support structure geometries. The improvements concerning the aerodynamic models will be mainly developed within the aerodynamics group. Coupling these improved aerodynamic models to structural dynamic models will improve the results obtained from simulations. There is also room for improvement in the currently used structural models. Therefore for certain cases the aerodynamic models should be coupled to current state-of-the-art structural dynamic codes (multi-body of FEM). To enable a straightforward coupling the ECN Aero-module is currently being developed. This module will also be coupled to two existing aeroelastic codes that ECN currently has: TURBU and PHATAS. This way these codes will also benefit from new aerodynamic models that are developed and incorporated in the Aero-module.

The improvements in the structural dynamic models are mainly needed for the drive train and the offshore support structures. It is clear that using a more complex structural and/or aerodynamic model results in an increase in the calculation time.

Improved reliability of the codes can only be verified by extensive validation of the programs. Therefore the ECN Aero-module coupled to different structural codes and using different structural models will be compared to measurements.