Experimental study of the effect of a slat on the aerodynamic performance of a thick base airfoil

There is continuous effort to try and improve the aerodynamic performance of wind turbine blades. This experimental study focusses on the addition of a passive slat on a thick airfoil typically used in the inboard part of commercial wind turbine blades. Nine different slat configurations are considered, with both a clean and tripped main airfoil. The results are compared with the performances of the airfoil without slat, as well as the airfoil equipped with vortex generators. It is found that, when the airfoil is clean, the increase in lift-to-drag ratio due to the presence of a slat is larger than when vortex generators are used. This is also true for the tripped airfoil, but only at small angles of attack. As expected, in all configurations, the presence of the slat delays flow separation and stall. Finally, for a clean airfoil and small angles of attack, the slat decreases the lift-to-drag ratio of the main airfoil only. By contrast, as the angle of attack increases, it seems that the slat changes the flow field around the main airfoil in such a way that its lift-to-drag ratio becomes larger than for the airfoil without slat. These effects are less pronounced when the airfoil is tripped. This work helps to better understand the role of slat in improving the aerodynamics of blade sections. It can also be used to validate simulation tools in the field.

Development of thick airfoils for outboard sections and investigation into their application for large rotors

The use of thick airfoils toward the outboard part of horizontal axis wind turbine blades is a promising concept to reduce the cost of wind energy. In fact, thick airfoils have higher area moments of inertia than those of thin airfoils, normally employed toward the outboard part of the blade. Replacing thin airfoils with thicker ones would therefore allow one to improve the structural properties of the blade, reducing the mass needed to ensure its structural integrity. Conventional thick airfoils, however, are generally characterized by worse aerodynamic performance with respect to those of thin airfoils, which make them less attracting for their use toward the outboard part of the blade. The research reported in this paper deals with the development of an optimization system for the aerodynamic design of thick airfoils, aiming to improve their aerodynamic performance, and therefore making them more suitable for their usage toward the outboard part of the blade. In order to determine the effect of the use of thick airfoils towards outboard sections, a blade design incorporating a newly designed 30% thick airfoil is assessed both statically and dynamically. The results showed that mass reduction can be achieved with the use of ad hoc optimized thick airfoils with limited penalty in power production.