分形扰流片的气动声学性能
One of the major environmental problems facing the aviation industry is that of aircraft noise. The workpresented in this paper, done as part of the EU’s OPENAIR Project, looks at reducing spoiler noise whilstmaintaining aerodynamic performance, through means of large-scale fractal porosity. It is hypothesised thatthe highly turbulent flow generated by fractal grids from the way the multiple-length-scales are organised inspace, 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 andis less offensive to the human ear. A total of nine laboratory scaled spoilers were looked at, seven of whichhad a fractal design, one with a regular grid design and one solid for reference. The spoilers were inclined atan angle of 30. Force, acoustic and flow visualisation experiments on a flat plate were carried out and it wasfound that the present fractal spoilers reduce the low frequency noise by 2.5dB. Results show that it is possibleto improve the acoustic performance by modifying a number of parameters defining the fractal spoiler, someof them very sensitively. From these experiments, two fractal spoilers were chosen for a detailed aero-acousticstudy on a three-element wing system, where it was found that the fractal spoilers had a reduction of up to 4dBin the sound pressure level while maintaining similar aerodynamic performances as conventional solid spoilerson the measured wing system.