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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Advanced rotor technologies' taking place on Tuesday, 11 March 2014 at 11:15-12:45. The meet-the-authors will take place in the poster area.

Lars C. Henriksen DTU Wind Energy, Denmark
Co-authors:

(1) DTU Wind Energy, Roskilde, Denmark

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Lars Christian Henriksen received his M.Sc. degree in 2007 electrical engineering from the Technical University of Denmark. In 2011 he received his Ph.D. degree from Risø National Laboratory for Sustainable Energy, Technical University of Denmark. He is currently employed as a Research Scientist at the Technical University of Denmark where he works with his main areas of interest: Control theory, in particular model-based control and fault diagnosis of wind turbines. He is also working on novel concepts including Lidars, trailing edge flaps and floating wind turbines.

Abstract

Is pitch system free play and friction important for rotor design?

Introduction

With increasingly larger, flexible and advanced rotor designs including pre-bend, sweep etc., the influence of subcomponent characteristics on the turbine loads, stability and performance is becoming increasingly important. Therefore, there is a gaining interest in aero-elastic simulations that couples subcomponent models to aero-elastic computations. An example is integrated design of blades and pitch systems. The value of integrated models is illustrated by studying the effect of the free-play/backlash in a pitch gear and the blade bearing friction on loads, stability and performance. The study is based on a coupled model of a pitch system and an aero-elastic turbine model.

Approach

A parametric pitch gear model is derived, that is highly nonlinear and captures both the free-play/backlash and the friction in the pitch gear and bearing. The pitch gear model is coupled to a full aero-elastic model using a new build-in framework for coupling external system of differential equations to the aero-elastic model. With the coupled parametric model, the turbine loads and performance are studied through load simulations with different pitch parameters.

Main body of abstract

Models of three different pitch gear configurations are simulated. The models are derived from data provided by a pitch gear manufacturer and represent the following pitch gear configurations: cycloidal without free-play, cycloidal with free-play, and planetary with free-play. Load simulations are performed with standard collective pitch control for comparing loads and performance. A parameter study is made to assess the sensitivity of the loads and performance to the gear ratio. Furthermore, simulations are performed with cyclic pitch control. Finally, simulations are performed with advanced rotor designs such as highly flexible swept blades. For the standard collective pitch configuration it is seen that there is limited difference in performance and loads between the three pitch gears. The sensitivity study shows that the planetary gear exhibits the greatest sensitivity to gear ratio, and the performance is highly affected by the mechanics of the planetary pitch gear at low gear ratios. Little difference in performance and loads is observed for the IPC simulations with the different pitch gears for a rather stiff and straight blade. However, swept blade designs yield higher loads on the pitch gear because of the additional blade torsion that is introduced along with the sweep, and the higher flexibility of blades causes high nonlinearities e.g. due to varying moment of inertia with blade bending. Thus, the coupled model can be used for exploring new pitch gear types and configurations that are tailored for specific advanced rotor designs.

Conclusion

In this paper, it is shown how the coupled aero-elastic models can be applied for detailed design studies. By simulating a full aero-elastic model coupled with an external pitch gear model, it is illustrated and exemplified how complex sub-components can be included in integrated simulations models, and how this changes the load- and stability characteristics. This approach can be applied for numerous types of sub-components for assessing the influence of specific component properties on the loads and performance of a turbine.


Learning objectives
The paper aims at:
- Putting focus on the value of coupled design analysis
- Demonstrate the ability of coupling aero-elastic models with external systems.
- Assess the effects of pitch gear properties on turbine performance, stability and loads through integrated modeling