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The effect of large-eddy breakup devices on flow noise

Published online by Cambridge University Press:  26 April 2006

A. P. Dowling
A. P. Dowling
Affiliation:
The University Engineering Department, Trumpington Street, Cambridge CB2 1PZ, UK
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Abstract

The installation of large-eddy breakup devices (LEBUs) or ‘flow manipulators’ in a turbulent boundary layer over a rigid plane surface is known to lead to reductions in skin-friction coefficient, turbulence intensity and fluctuating Reynolds stress. We investigate the effect of such devices on the surface pressure spectrum and the far-field sound radiation. A model problem, in which a two-dimensional elliptical vortex is convected past a LEBU, is solved analytically in the low-Mach-number limit. The main noise source mechanisms are identified in this idealized problem and we go on to obtain scaling laws for the sound produced by a turbulent boundary-layer flow over a LEBU. The introduction of a LEBU reduces the strength of the Lighthill quadrupole source terms, but it produces an additional dipole source. However, the pressure fluctuations in this dipole field decay rapidly with distance from a LEBU, and we find that an array of LEBU's could have a beneficial effect on the flow noise for radian frequencies which are large in comparison with c/30Δ, where c is the sound speed and Δ denotes the boundary-layer thickness. At lower frequencies the LEBUs are predicted to increase the flow noise.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 208 , November 1989 , pp. 193 - 223
Copyright
© 1989 Cambridge University Press

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