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One of the major environmental problems facing the aviation industry is that of aircraft noise. The work
presented in this paper, done as part of the EU’s OPENAIR Project, looks at reducing spoiler noise whilst
maintaining aerodynamic performance, through means of large-scale fractal porosity. It is hypothesised that
the highly turbulent flow generated by fractal grids from the way the multiple-length-scales are organised in
space, would reduce the impact of the re-circulation region and with it, the low frequency noise it generates.
In its place, a higher frequency noise is introduced which is more susceptible to atmospheric attenuation and
is less offensive to the human ear. A total of nine laboratory scaled spoilers were looked at, seven of which
had a fractal design, one with a regular grid design and one solid for reference. The spoilers were inclined at
an angle of 30. Force, acoustic and flow visualisation experiments on a flat plate were carried out and it was
found that the present fractal spoilers reduce the low frequency noise by 2.5dB. Results show that it is possible
to improve the acoustic performance by modifying a number of parameters defining the fractal spoiler, some
of them very sensitively. From these experiments, two fractal spoilers were chosen for a detailed aero-acoustic
study on a three-element wing system, where it was found that the fractal spoilers had a reduction of up to 4dB
in the sound pressure level while maintaining similar aerodynamic performances as conventional solid spoilers
on the measured wing system.
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