City Research Online

Abstract

This paper presents an acoustic study of a standard NACA 0012 aerofoil with additional self-oscillating passive flaplets attached to the trailing edge. The tests with varying geometries of the flaplets were conducted in the anechoic wind tunnel at Brandenburg University of Technology, at chord based Reynolds numbers, $Re_c = 100,000 - 900,000$ at three geometric angles of attack $\alpha_g = 0^\circ, 10^\circ$ and $15^\circ$. It was observed that all flaplet configurations reduce tonal noise and that the key geometric parameter to reduce this noise component is the width of the flaplets. The narrowest configuration tested almost completely removed the tonal noise, leading to an average overall sound pressure level reduction of up to 9 dB across the entire $Re_c$ range at $\alpha_g = 10^\circ$. It was also observed that, in the low frequency regime, a further noise reduction can be achieved by tuning the natural frequency of the oscillating flaplets. The thereby affected frequency range in the noise spectrum moves to higher frequencies when the natural frequency of the flaplets is increased and vice versa. Hence we show a novel way to target specific frequencies in passive aerofoil self-noise cancellation.

Publication Type:	Article
Additional Information:	© 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
Publisher Keywords:	Aeroacoustics, Bioinspiration, Self-oscillating flaplets, Aerofoil self-noise
Subjects:	Q Science > QC Physics T Technology > TJ Mechanical engineering and machinery T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Science & Technology > Engineering
SWORD Depositor:	Symplectic Administrator

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