Splitter-plates to Reduce Drag and Noise of a Flatback Thick Airfoil for Wind Turbine Blades

The inboard section of wind turbine blades requires very thick airfoils, whose performance in terms of C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</inf> can be improved with a flatback trailing edge in order to reduce the adverse pressure gradient. On the other hand, this solution hugely increases aerodynamic drag and noise, and to address these issues, the use of a splitter-plate has been proposed in the past. However, traditional splitters aligned with the chord-line are unable to avoid a drop in C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</inf>, due to the reduction in the degree of cambering of the resulting overall geometry. In this study we use 2D CFD to analyze the behavior of a splitter characterized by a downward slope with respect to the chord-line; it is applied to an airfoil having maximum thickness of 30% and flatback trailing edge thickness of 10%. The results of the investigation, conducted for different lengths and slopes of the splitter and for different Re, show that it is possible to achieve significant reduction in drag (up to 26%), in aerodynamic force fluctuations (up to 90%) and in noise (up to 22 dB), while maintaining the same C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</inf> of the clean airfoil thanks to an improvement of the cambering brought by the splitter, if its length and slope are sufficient.