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An asymptotic theory of near-field propeller acoustics

Published online by Cambridge University Press:  26 April 2006

N. Peake  and
D. G. Crighton
N. Peake
Affiliation:
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street Cambridge CB3 9EW, UK
D. G. Crighton
Affiliation:
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street Cambridge CB3 9EW, UK
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Abstract

This paper presents expressions for the harmonic components of the near-field acoustic pressure of a B-bladed unswept single-rotation propeller. These are derived using asymptotic approximations to the standard radiation integrals for steady loading and thickness noise, under the assumption that B is large. The dependence of the pressure on blade operating conditions (both supersonic and subsonic) is described by simple formulae, which provide significant insights into the mechanisms of sound generation by rotating bodies. For supersonic motion, the importance of sources satisfying the Ffowcs Williams & Hawkings sonic condition is demonstrated, whilst for subsonic blades the near-field noise is proved to be tip-dominated. Expressions for the noise (valid from close to the tips right out to infinity) are given in both cases, requiring matching across an Airy function smoothing region when the tips move subsonically. Excellent agreement between the asymptotic formulae and both full numerical evaluations (with a considerable saving in CPU time) and experimental data is achieved.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 232 , November 1991 , pp. 285 - 301
Copyright
© 1991 Cambridge University Press

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