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The effect of gravity on a shaped sonic boom

Published online by Cambridge University Press:  03 February 2016

T. Cain
T. Cain*
Affiliation:
[email protected], Gas Dynamics Ltd, Farnborough, UK
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Abstract

Previously it was demonstrated that gravity is directly responsible for the attenuation of sonic booms as they propagate towards the ground, while the gradient in acoustic impedance has no effect on the wave strength. This was a significant departure from the well accepted acoustic theory and naturally led to questions concerning comparison with experiment and the implications for low boom design. This paper presents a comparison of measured ground signatures of the Northrup-Grumman Shaped Sonic Boom Demonstrator (SSBD) with a method of characteristics extrapolation from a close proximity flight measurement of static pressure under the aircraft. Comparison is also made with Whitham’s theory, extended to include gravity and the ambient temperature variation, as presented in the previous paper. The calculations are both in good agreement with the experimental ground signature. The usual equations that define the acoustic propagation (gravitational body force neglected) are transformed so that the computational algorithms of the extended Whitham theory are applicable. The transformation simplifies the acoustic model and reveals the conditions under which the errors in its prediction will be large. At the Mach number of 1.4, corresponding to the SSBD flight, the error is relatively small and the acoustic prediction is also in close agreement with the ground signature.

Type
Research Article
Information
The Aeronautical Journal , Volume 114 , Issue 1160 , October 2010 , pp. 651 - 656
Copyright
Copyright © Royal Aeronautical Society 2010 

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