LECTURE 15 
SOME CONTRIBUTIONS FROM AERONAUTICS TO THE FIELD 
OF UNDERWATER NOISE 
E.J. Richards, J. L. Willis, and D.J.M. Williams 
Department of Aeronautics and Astronautics 
University of Southampton 
Southampton, England 
15.1. INTRODUCTION 
During the last fifteen years, the introduction of jet engines into civil aircraft 
operation has accentuated the problem of noise in aviation, and many investiga - 
tions have been made which are of distinct significance in the apparently distant 
field of underwater noise. For example, withthe growth of aircraft engine power, 
the speeds of aircraft have increased to such a degree that the rough boundary 
flow along the fuselage gives rise to the majority of the noise inside the cabin; 
it gives rise to fuselage vibrations which can in certain circumstances cause 
skin cracks and fuselage and wing failures, and it is suspected that the radiated 
noise from the fuselage movement may have some effect on transition from 
laminar flow on neighboring surfaces. The noise radiated from such fuselages 
is very much a function of the modes of oscillation and the degree of damping, 
both structural and acoustic, involved in these particular modes. In the field of 
engine design also, such problems arise. It is known that compressor noise has 
a large random content which is related to the boundary-layer pressure fluctua - 
tions on the blades and is caused by the unsteadiness of the flow incident upon 
them. This problem of noise radiated from blades is now arousing major interest 
in engine design. 
The knowledge gained from investigation of these various factors is often 
directly applicable to analogous problems in underwater noise. For instance, 
the problem of the boundary-layer noise radiated from the hull of a vessel is 
closely related to that of radiation from a fuselage boundary layer; the effects 
of pressure gradients, waviness, rivets, roughness, skin discontinuities, and so 
on, have their obvious equivalents. Similarly, the skin response to boundary-layer 
pressure fluctuations has an exact analogy in the self-noise within an Asdic 
dome, and in the structural vibration of a submarine. Still further, the use of 
correlation techniques and fuselage damping to identify and supress fuselage 
vibrations must also be of interest to naval personnel seeking to reduce the 
reradiation of noise from their craft. 
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