In the literature, several recent studies, both numerical and experimental, involved finlet fences, while only one publication examined the aeroacoustic behaviour of finlets of a geometry alternative to fences, the so-called finlet rails. The results on the aeroacoustic performances of the finlet rails from the aforementioned sole work evidenced that this geometry can lead to higher levels of noise attenuation compared with the finlet fences. However, only a limited number of configurations was tested so far, and absolutely no quantifications were reported in relation to how the surface treatment affects the drag coefficient. Another aspect that was left unexplored is the mechanism by which finlet rails produced a noise mitigation, and how the flow field around the airfoil with inserts is modified in consequence of bespoke treatment. These aspects were for first time addressed in this project.
The research results on finlet fences presented some remarkable elements of novelty and breakthrough findings too. A wider range of configurations, in terms of finlets height and transversal spacing, was in fact tested compared to past analyses. And for each configuration, both the far-field noise spectrum and the drag coefficient of the airfoil were measured as a function of of the angle of attack and the Reynolds number. It was found that the transversal spacing has a stronger impact on the noise mitigation than the height, while the opposite is true for the drag coefficient, with the height being dominant. This is a very important finding, as it suggests that an optimum exists in the design of the finlet fences, which maximizes the aeroacoustic performances and minimizes the drag penalty.
Overall, the potential socio-economic impact of this research lies in the attenuation of the acoustic emissions of aircrafts and of on-shore wind turbines, while minimizing the inevitable penalties in terms of drag, and thus the reduced efficiency associated with these treatments. Civil aviation and clean energy are sectors that have experienced a considerable increase in the past decade, and that are pivotal to the wealth of the European Union in the years ahead. Reducing their impact on civilians is the main long-term achievement that this project is envisaged to produce, with the ultimate goal to make air transportation sustainable, and to accelerate the transition from fossil fuels to renewable sources of energy, such as wind energy is.
