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Aeroacoustics

Published online by Cambridge University Press:  04 July 2016

J. E. Ffowcs Williams
J. E. Ffowcs Williams*
Affiliation:
Department of EngineeringUniversity of CambridgeCambridge, UK
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Summary

The high noise levels of early turbojet aircraft forced attention to be given to the mechanics of the noise generation process and ways were urgently sought for silencing their high speed propulsive flows. The subject of aeroacoustics was born with this problem, the subject being the variety of ways in which sound and flow interact, with the early emphasis being on sound generated aerodynamically. Sound was thought to be a by-product of the flow arid believed to have a negligible back-reaction on it.

The search for noise suppression has been extremely successful, so much so, that engine noise is no longer a problem likely to constrain future aircraft operations. Silencing technology has made enormous strides by avoiding as much as possible the very high speed jet flows that were a feature of early engines. But that avenue is not available to supersonic aircraft, which still wait for ways of making their operation acceptably quiet to be identified.

Aeroacoustics has brought into being a much deeper insight into the interactions of sound and flow, and some of the early presumptions about the mechanisms of noise creation have had to be rethought. Some of the advances have come from entirely new directions, for example, from anti-sound, a silencing idea based on the destructive cancellation of interfering waves, which has advanced to a state that provides a useful new technology. Some new understanding follows the discovery that flow-acoustic interactions are not always the one-way process previously assumed. Sound can affect flow, especially so when the flow is unstable. It is of course the very unstable flows that make most noise so, taken together, these developments indicate that control might one day be exercised by actively managing the unsteady flows, making them more useful and desirable than before. Indeed examples are now known where control has made possible the avoidance of a powerful performance-limiting instability that previously made that flow regime a prohibited operational zone, a development of aeroacoustics that is probably far more significant than its noise suppression role. That line of thought is expanded in this paper, which concludes with the speculation that active control might now be offering an avenue for approaching die high speed jet noise problem from a completely new direction. Of course it is far too early to know whether that approach can provide a way for removing the take-off noise constraint currently threatening the viability of supersonic transports, but it might; that makes it very important indeed, for it is hard to see any alternative.

Type
Research Article
Information
The Aeronautical Journal , Volume 100 , Issue 1000 , December 1996 , pp. 530 - 537
Copyright
Copyright © Royal Aeronautical Society 1996 

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References

1. Fleming, N. The silencing of aircraft, J Roy Aeronaut Soc, 1946, 50, pp 639–663.Google Scholar
2.Lord Rayleigh Theory of Sound (2 vols), 2nd edn, Macmillan, London, 1896.Google Scholar
3. Lighthill, M.J. On sound generated aerodynamically. I. General theory, Proc Roy Soc A, 1952, 211, pp 564–587.also Lighthill M.J. On sound generated aerodynamically: II. Turbulence as a source of sound, Proc Roy Soc A, 1954, 222, pp 1-32.Google Scholar
4. Smith, M.J.T. Aircraft Noise, Cambridge Aerospace Series, Cambridge University Press, 1989.Google Scholar
5.Noise Mechanisms, AGARD Conference Preprint No 131, Nato, 1973.Google Scholar
6. SirHooker, Stanley, Not Much of an Engineer, Airlife Publishing, 1984, pp 140–159.Google Scholar
7. Whitfield, O.J. Novel Schemes for Jet Noise Control, PhD Thesis, Cambridge University, 1975.Google Scholar
8. Carpenter, P.W. The effects of swirl on the performance of supercritical convergent-divergent nozzles, May 1981, Aeronaut Q, 32, pp 126–152.Google Scholar
9. Smith, M.J.T. Where to with aircraft noise control? World Aerospace Technology International 95, pp 32–35.Google Scholar
10. Moore, C.J. The role of shear layer instability waves on jet exhaust noise, J Fluid Mech, 1977, 80, pp 321–367.Google Scholar
11. Bechert, D. and Pfizenmaier, E. On the amplification of broad band jet noise by pure tone excitation, J Sound Vib, 1957, 43, pp 581–587.Google Scholar
12. Ffowcs Williams, J.E. and Gordon, C.G. Noise of highly turbulent jets at low exhaust speeds, AlAA J, April 1965, 3, (4), pp 791–793.Google Scholar
13. Pannu, S.S. and Johannesen, N.H. The structure of jets from notched nozzles, J Fluid Mech, 1976, 74, pp 515–528.Google Scholar
14. Crighton, D.G., Ffowcs Williams, J.E. and Cheeseman, I.C. The outlook for simulation of forward flight effects on aircraft noise, J Aircr, 1977, 14, (11).Google Scholar
15. Michalke, A. and Michel, U. Relation between static and in-flight directivities of jet noise, J Sound Vib, 1979, 63, pp 602–605.also Michalke A. and Michel U. Prediction of jet noise in flight from static tests, J Sound Vib, 1979, 67, pp 341-367.Google Scholar
16.The flight effect of Michalke and Michel vis-á-vis Lighthill's model, letters to the editor, J Sound Vib, 1979, 67, (3), pp 425–431.Google Scholar
17. Hawkins, R. and Hoch, R. Studies into Concorde's engine noise, emission and reduction, Proceedings of 10th International Aeronautical Congress, Paris, 1971.Google Scholar
18. Lueg, P. Process of silencing sound oscillations, US Patent No 2,043,416, 1936.Google Scholar
19. Swinbanks, M. A. The active control of sound propagation in long ducts, J Sound Vib, 1973, 27, p 411.Google Scholar
20. Ross, C.F. Active Control of Sound, PhD Thesis, Cambridge University, 1980.Google Scholar
21. Guicking, D. Active Noise and Vibration Control, Reference Bibliography, 3rd Edn, University of Gottingen, 1988 Google Scholar
22. Dines, P.J. Active Control of Flame Noise, PhD Thesis, Cambridge University, 1984.Google Scholar
23. Stansell, J. Anti-sound heralds a silent era, Science-Technology- Industry “Link up”, 14-16, July-Sept 1985, Home & Law Scientific Publications.Google Scholar
24. Heckl, M. Active Control of the Rijke Tube, PhD Thesis, Cambridge University, 1985.Google Scholar
25. Bloxsidge, G.J., Dowling, A.P., Hooper, N. and Langhorne, P.J. Active control of reheat buzz, AlAA J, 1988, 26, pp 783–790.Google Scholar
26. Huang, X.Y. Active control of aerofoil flutter, AlAA J, 1987, 25, (8), p 1126.Google Scholar
27. Ffowcs Williams, J.E. and Zhao, B.C. The active control of vortex shedding, J Fluids Structures, 1989, 3, pp 115–122.Google Scholar
28. Roussopoulos, K. Feedback control of vortex shedding at low Reynolds numbers, J Fluid Mech, 1993, 248, pp 267–296.Google Scholar
29. Sunyach, M. and Ffowcs Williams, J.E. The active suppression of oscillation in flow-excited cavities, CR Acad Sc Paris, 303, Serie II, 12, pp 1085–1088, 1986.Google Scholar
30. Emmons, H.W., Pearson, C.E. and Grant, H.P. Compressor surge and stall propagation, Transactions of the ASME, 77, pp 455–469.Google Scholar
31. Epstein, A.H., Ffowcs Williams, J.E. and Greitzer, E.M. Active suppression of compressor instabilities, AlAA 10th Aeroacoustics Conference, Paper No AIAA-86-1994, 1986.Google Scholar
32. Ffowcs Williams, J.E. and Huang, E.Y. Active stabilisation of compressor surge, J Fluid Mech, 1989, 204, pp 245–262.Google Scholar
33. Day, I.J. Stall inception in axial flow compressors, J Turbomachinery, 1993, 115/1, pp 1–9.Google Scholar
34. Ffowcs Williams, J.E. and Graham, W.R. An engine demonstration of active surge control, Presented at the Gas Turbine and Aeroengine Congress and Exposition, Brussels, Belgium, 1990.Google Scholar