<DOC>
<DOCNO>
219
</DOCNO>
<TITLE>
on the strength distribution of noise sources along
a jet .
</TITLE>
<AUTHOR>
ribner,h.s.
</AUTHOR>
<BIBLIO>
utia r51, 1958.
</BIBLIO>
<TEXT>
  the spatial distribution of noise sources along a jet is
investigated by application of lighthill's
theory to regions of 'similar'
profiles .  the analysis refers to the
noise power emitted by a 'slice' of
jet (section between two adjacent planes
normal to the axis) as a function
of distance x of the slice from the nozzle .
it is found that this power
is essentially constant with x in the initial
mixing region (x law), then
further downstream (say 8 or 10 diameters
from the nozzle) falls off
extremely fast (x law or faster) in the
fully developed jet .  because
of this striking attenuation of strength
with distance, it is concluded that
the mixing region produces the bulk of
the noise and must dominate in
muffler behavior,. conversely, the 'fat'
part of the jet must contribute
much less to the total noise power than is commonly supposed .
  powell's experiments on the effects of nozzle velocity profile
on total noise power are interpreted
qualitatively .  the behavior of
multiple-nozzle or corrugated mufflers,
both as to overall quieting and
frequency-shifting, is also interpreted
in the light of the results .  the
possibility emerges that such mufflers
may be improved without serious
thrust loss by the addition of a sound-attenuating shroud .
</TEXT>
</DOC>
