Journal cover Journal topic
Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
Wind Energ. Sci., 2, 241-256, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research articles
16 May 2017
An investigation of unsteady 3-D effects on trailing edge flaps
Eva Jost, Annette Fischer, Galih Bangga, Thorsten Lutz, and Ewald Krämer Institute of Aerodynamics and Gas Dynamics, University of Stuttgart, Pfaffenwaldring 21, 70569 Stuttgart, Germany
Abstract. The present study investigates the impact of unsteady 3-D aerodynamic effects on a wind turbine blade with trailing edge flap by means of computational fluid dynamics (CFD). Harmonic oscillations are simulated on the DTU 10 MW rotor with a morphing flap of 10 % chord extent ranging from 70 to 80 % blade radius. The deflection frequency is varied in the range between 1 and 6 p. To quantify 3-D effects, rotor simulations are compared to 2-D airfoil computations and the 2-D theory by Theodorsen. It was found that the deflection of the flap on the 3-D rotor causes a complex wake development and induction which influences the loads over large parts of the blade. In particular, the rotor near wake with its trailing and shed vortex structures revealed a great impact. Trailing vorticity, a 3-D phenomenon, is caused by the gradient of bound circulation along the blade span. Shed vorticity originates from the temporal bound circulation gradient and is thus also apparent in 2-D. Both lead to an amplitude reduction and shed vorticity additionally to a hysteresis of the lift response with regard to the deflection signal in the flap section. A greater amplitude reduction and a less pronounced hysteresis is observed on the 3-D rotor compared to the 2-D airfoil case. Blade sections neighboring the flap experience, however, an opposing impact and hence partly compensate for the negative effect of trailing vortices in the flap section with respect to integral loads. Comparisons to steady flap deflections at the 3-D rotor revealed the high influence of dynamic inflow effects.

Citation: Jost, E., Fischer, A., Bangga, G., Lutz, T., and Krämer, E.: An investigation of unsteady 3-D effects on trailing edge flaps, Wind Energ. Sci., 2, 241-256,, 2017.
Publications Copernicus
Short summary
Trailing edge flaps applied to the outer part of a wind turbine rotor blade are a very promising concept to reduce fatigue loads as they are able to increase or decrease the airfoil lift for a given angle of attack. They have been widely researched on 2-D airfoils, but only little is known about their aerodynamic characteristics on 3-D wind turbine rotor blades. The present article addresses this issue.
Trailing edge flaps applied to the outer part of a wind turbine rotor blade are a very promising...