Abstract
The turbulent atmospheric boundary layer in which wind turbines are implemented is strongly inhomogeneous and unsteady. This induces unsteady mechanical loads at different characteristic time scales from seconds to minutes which limits significantly their life time. Different control strategies have been proposed in the framework of the French ANR SmartEole project to alleviate the impact of these upstream fluctuations at the farm, wind turbine and blade scales (i.e. characteristic time scales from seconds to minutes). The present work, which is part of this ANR project, focuses on the flow control strategies at the blade scale, to manipulate lift and thus alleviate fatigue loads. The design of a NACA654-421 airfoil profile has been modified to be able to implement jet control. Slotted jet and discrete jet configurations were implemented numerically and experimentally respectively. Results show the ability of both configurations to increase the lift by up to 30% using a significant redistribution of the mean shear. Efficiency seems to be more important using slotted jets, which however needs to be confirmed from 3D simulations.
Highlights
In the last few decades many different flow control configurations were investigated with different objectives depending on the application
They can be classified in two categories: circulation control and control of separated turbulent boundary layer flows
Perturbations that arises on wind turbine blades can be viewed as a dynamic modification of the flow configuration
Summary
In the last few decades many different flow control configurations (flat plates, ramps, bumps, ducts, airfoils, wind turbines ....etc) were investigated with different objectives depending on the application. The design of a NACA654-421 airfoil profile has been modified (see figure 1) to adapt the lift to perturbations, by manipulating a separated turbulent boundary layer flow and taking advantage of Coanda effect from circulation control. Particle image velocimetry Mean velocity fields around the airfoil trailing edge were studied from 2D PIV measurements in order to analyze flow topology with and without jet control in longitudinal planes of the airfoil model. Pressure measurements around the chord in the jet control airfoil is obtained using the pressure integration of surface squared holes (diameter D = 1mm) in each transverse line To validate this unusual procedure, pressure measurements were measured against pressure measurements from the PRISME airfoil (see for example figure 6b). These results are found sufficient to compare control effect presented below
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