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Published online by Cambridge University Press: 28 July 2016
Before discussing the noise associated with supersonic flight, it is pertinent to restate the sources of noise at subsonic speeds.
As Lilley has pointed out, noise at subsonic speeds is due to turbulence, such as occurs in jets, wakes, boundary layers, and regions of separation, and to vortices and regions of shear flow. In all these types of flow viscosity plays a predominant part, and therefore at subsonic speeds the noise of an aircraft depends very much upon the viscosity of the fluid: in an inviscid fluid, an aircraft would make no noise, because, at subsonic speeds, the pressure changes induced by its motion would be too gradual to be audible.
Note on page 240 * Some Aspects of the Noise Propagation from Supersonic Aircraft. G. M. Lilley, R. Westley, A. H. Yates, and J. R. Busing. Journal of the Royal Aeronautical Society, June 1953.
Note on page 242 * Powell, A. (1951). A Schlieren study of small scale air jets and some noise measurement on two-inch diameter air jets. A.R.C. 14726, December 1951.
Note on page 242 † Powell, A. (1952). On the noise emanating from a two-dimensional jet above the critical pressure. A.R.C. 15472, June 1952; Aeronautical Quarterly, February 1953.
Note on page 242 ‡ Powell, A. (1952). On the mechanism and reduction of choked jet noise. A.R.C, 15623, December 1952.
Note on page243 * Powell, A. (1952). Edge tones and associated phenomena. A.R.C 15333, October 1952.