Hostname: page-component-cd9895bd7-dzt6s Total loading time: 0 Render date: 2024-12-29T14:03:55.385Z Has data issue: false hasContentIssue false
  • English
  • Français

The acoustics of turbulence near sound-absorbent liners

Published online by Cambridge University Press:  29 March 2006

John E. Ffowcs Williams
John E. Ffowcs Williams
Affiliation:
Department of Mathematics, Imperial College, London
Get access Rights & Permissions [Opens in a new window]

Abstract

Acoustic liners are often perforated screens backed by sound-absorbent material. Turbulence can interact with these screens to generate additional sound. The dynamics of the generation process is examined in this paper, where the liner is modelled as an infinite rigid plane boundary with a homogeneous array of circular orifices or rigid pistons. The acoustic properties of these boundaries are derived in the long wavelength limit. Small-scale turbulence is scattered by individual apertures into sound. Acoustically transparent surfaces support dipole scattering centres while more ‘opaque’ surfaces have monopoles at the apertures which convert turbulence into sound more effectively. It is shown that the process can be described once the response of an individual aperture in an infinite baffle is known. At low Mach numbers the screen can increase the sound radiated by adjacent turbulence by a factor equal to the inverse fourth power of the Mach number. Mean-flow effects are ignored but they are thought to increase the effects deduced in this preliminary study.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 51 , Issue 4 , 22 February 1972 , pp. 737 - 749
Copyright
© 1972 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Benjamin, T. B. 1963 The threefold classification of unstable disturbances in flexible surfaces bounding inviscid flows. J. Fluid Mech. 16, 436.Google Scholar
Copson, E. T. 1947 On the problem of the electrified disk. Proc. Edinb. Math. Soc. 3 (8), 14.Google Scholar
Curle, N. 1955 The influence of solid boundaries upon aerodynamic sound. Proc. Roy. Soc. A 231, 412.Google Scholar
Ffowcs Williams, J. E. 1965 Sound radiation from turbulent boundary layers formed on compliant surfaces. J. Fluid Mech. 22, 347.Google Scholar
Hughes, R. G. 1970 Some acoustic properties of porous surfaces. D.I.C. thesis, Imperial College London.
Lanb, H. 1925 The Dynamical Theory of Sound. Constable.
Leppington, F. G. & Levine, H. 1971 Reflection and transmission at a plane screen with periodically arranged circular perforation. To appear.
Lighthill, M. J. 1952 On sound generated aerodynamically. I. General theory. Proc. Roy. Soc.
Mechel, F. 1960 Schalldämpfung und Schallverstarking in Luftstromungcn durch Absorbierend Ausgekleidete Kanäle. Acustica, 10, 133–148.Google Scholar
Mechel, F., Mertens, P. & Schilz, W. 1962 Research on sound propagation on sound absorbent ducts with superimposed airstreams. 4 volumes. Tech. Doc. Rep. AMRL-TDR-62-140.
Miles, J. W. 1956 On the reflection of sound at an interface of relative motion. J. Acoust. Soc. Am. 29, 226.Google Scholar
Powell, A. 1960 Aerodynamic noise and the plane boundary. J. Acoust. Soc. Am. 32, 8982.Google Scholar
Rayleigh, Lord 1896 The Theory of Sound. Macmillan.