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The aerodynamic noise of small-perturbation subsonic flows

Published online by Cambridge University Press:  29 March 2006

Roy Amiet  and
W. R. Sears
Roy Amiet
Affiliation:
Cornell University
W. R. Sears
Affiliation:
Cornell University
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Abstract

The method of matched asymptotic expansions is used to simplify calculations of noise produced by aerodynamic flows involving small perturbations of a stream of non-negligible subsonic Mach number. This technique is restricted to problems for which the dimensionless frequency ε, defined as ωb/a0, is small, ω being the circular frequency, b the typical body dimension, and a0 the speed of sound. By combining Lorentz and Galilean transformations, the problem is transformed to a space in which the approximation appropriate to the inner region is found to be incompressible flow and that appropriate to the outer, classical acoustics. This approximation for the inner region is the unsteady counterpart of the Prandtl-Glauert transformation, but is not identical to use of that transformation in a straightforward quasi-steady manner. For wings in oscillatory motion, it is the same approximation as was given by Miles (1950).

To illustrate the technique, two examples are treated, one involving a pulsating cylinder in a stream, the other the impinging of plane sound waves upon an elliptical wing in a stream.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 44 , Issue 2 , 11 November 1970 , pp. 227 - 235
Copyright
© 1970 Cambridge University Press

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