<DOC>
<DOCNO>
209
</DOCNO>
<TITLE>
boundary layer induced noise in the interior of aircraft .
</TITLE>
<AUTHOR>
ribner,h.s.
</AUTHOR>
<BIBLIO>
utia r37, 1956.
</BIBLIO>
<TEXT>
  at high speeds the turbulent boundary layer washing the
airplane fuselage excites appreciable skin vibration, promoting strong
noise in the interior .  the fluctuating exciting pressure distribution
can be represented as a pattern of moving waves (fourier integral) .
a running ripple in the skin follows underneath each wave, and the noise
is ultimately due to these ripples .
  the acoustic effects of the running ripples are calculated
for an infinite sheet,. this is considered the main result of the
paper .  supersonically moving ripples radiate strong sound in the form
of mach waves,. subsonically moving ripples radiate no sound .  formulas
for the mean square surface pressure and the energy flux are obtained
for an assumed idealized turbulent pressure spectrum .
  the results are adapted to provide a tentative estimate of
the noise generated at subsonic speeds in a practical fuselage .  the
running ripples are almost noise-free, but multiple reflections at the
frames and stringers promote standing waves .  an assumption is used
to link the two kinds of waves, and this leads to provisional
calculations of noise level ..  on this basis the noise level is
predicted to vary as for thin boundary layers, changing
progressively to for thick layers ( = external air
density, = speed, = layer thickness, = panel thickness) .  some
comparisons are made with experiment .  finally, an idea for
minimizing the noise is presented .
</TEXT>
</DOC>
