Abstract
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.
Highlights
The development of innovative add-ons, and their combination, are topics of high interest for wind turbine manufacturers. 15 Such devices can increase the energy yield of a wind turbine by a few percent, leading to potentially significant reductions in levelised cost of energy
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
Since vortex generators are commonly used to improve the performances of wind turbine blades, this paper presents results obtained when placing VGs on the main airfoil alone
Summary
The development of innovative add-ons, and their combination, are topics of high interest for wind turbine manufacturers. 15 Such devices can increase the energy yield of a wind turbine by a few percent, leading to potentially significant reductions in levelised cost of energy. A good example of such devices are low-drag vortex generators (VGs), which are typically used at the inboard or mid-board sections of the blade. At these locations, the airfoil sections are rather thick with a high maximum lift in order to 20 allow for the chord length to be reduced, without penalising greatly the overall energy yield. In order to mitigate this, and increase the lift-todrag ratio, vortex generators can be positioned in arrays in front of the separation line. These devices trigger the formation of small vortices in the boundary layer that re-energise the near-wall flow, preventing the flow to separate (Schubauer 25 and Spangenberg, 1960).
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