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Aerodynamic noise dependent on mean shear

Published online by Cambridge University Press:  28 March 2006

Ian S. F. Jones
Ian S. F. Jones
Affiliation:
Department of Mechanical Engineering, University of Waterloo, Waterloo, Ontario
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Abstract

New factors illustrating the effect of convection on acoustic radiation are deduced from Lighthill's theory of aerodynamic noise. For sound dependent on mean velocity variations for its generation, that is shear noise, the new factors are (1 − M cos θ)−3 and (1 − M cos θ)−1 in contrast with (1 − M cos θ)−5 for self noise.

Comparison with the measured far-field directionality patterns reported by Howes (1960) shows that the factor (1 − M cos θ)−3 provides considerably better agreement with the experimental observations than the self noise factor.

The source terms discussed by Lighthill (1954) when considering shear amplification are examined and shown to contain the terms produced by the analysis of Csanady (1966) as well as a new term dependent on the second derivative of the mean velocity.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 33 , Issue 1 , 12 July 1968 , pp. 65 - 72
Copyright
© 1968 Cambridge University Press

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References

Csanady, G. T. 1966 J. Fluid Mech. 26, 183.
Howes, W. L. 1960 N.A.S.A. T.R. R-52.
Lighthill, M. J. 1952 Proc. Roy. Soc. A, 211, 564.
Lighthill, M. J. 1954 Proc. Roy. Soc. A, 222, 1.
Williams, J. E. Ff. 1963 Phil. Trans. A, 255, 469.
Wills, J. A. B. 1964 J. Fluid Mech. 20, 417.