Lambie-type airfoil with coupled leading and trailing flap

The energy output of modern horizontal axis wind turbines increases with the radius squared. On the other hand, wind turbines face, amongs others, the challenge of fatigue due to gust loads. The larger the rotor, the more material has to be used to design the blade root accordingly, which increases turbine costs. Hence, the bigger a wind turbine, the more interesting are techniques to reduce the impact of gusts on the blade root. A field of research dealing with these techniques is called smart-rotor-control, where most prominent idea to be named is to reduce the gust load locally on the outer part of the wind turbine blade with a controlled trailing flap. Recent studies on this technique show reasonable load reductions. However, installing an active control system on the outer part of a wind turbine is challenging for several reasons. Actuators meeting the requirements are not easily found and reliably sensing the inflow conditions is difficult.

The research presented here, pursues the idea of a passive flap system that preserves the advantages of an active system without having its drawbacks. Starting point is an invention by Benjamin Lambie and Klaus Hufnagel of the Institute of Fluid Mechanics and Aerodynamics at the Technische Universität Darmstadt. Their device has a leading and a trailing flap coupled by a simple gearbox that uses the higher aerodynamic moments about the leading flap to control the trailing flap. It can be shown that the trailing flap angle has a big impact on the aerodynamic lift and the the angle of attack has a big impact on the aerodynamic moment about the leading flap. The later can hence be regarded as a sensor and the energy source for controling the trailing flap and therefore the lift.

Research Topic

While it can experimentally be shown that this principle works under steady conditions and it can theoretically deduced by the thin-airfoil theory, the main question prevails if this device can be used to alleviate random gust loads on a wind turbine blade. To answer this question several approaches are being followed:

1. Unsteady experiments are conducted by Ulrike Cordes from the Institute of Fluid Mechanics and Aerodynamics.

2. Fully coupled CFD-simulations by Sebastian Türk from the Department of Numerical Methods in Mechanical Engineering.

3. Panel-code simulations and frequency domain analysis by Henning Spiegelberg of the Dynamics and Vibrations Group.

The work of Henning Spiegelberg is the subject of this page and shell be described in more detail. The first part is to develop a two dimensional panel-code based on potential flow theory that allows to simulate an airfoil with a deforming outline. The deformation is coupled to a structural model. Using this approach simplifies the aerodynamic problem to a system of algebraic equations, which can be solved quite efficiently. Also this type of simulation allows a very simple description of random gust fields.

A second part consists in formulating the equations of motion for the airfoil under aerodynamic loading in the frequency domain. This analytical tool is even faster and allows to make simple parameter studies in a very efficient way. 


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Dolivostraße 15

D-64293 Darmstadt



+49 6151 16 - 24401 or 24402


+49 6151 16 - 24404




spiegelberg (at) gsc.tu...

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