Since the early 70’s, theories
have hinted that fan noise could be reduced by changing
the orientation of the fan outlet guide vanes. It wasn’t
until 1997, though, that tests in NASA Glenn’s
9’ x 15’ Low Speed Wind Tunnel proved those
theories right. NASA Glenn researchers, collaborating
with engineers from the Allison Engine Company, used
the traversing microphone system in the
9’ x 15’ Tunnel to measure noise levels of
a scale model fan stage in simulated takeoff and landing
conditions. The acoustic and aerodynamic measurements
recorded during these tests convincingly demonstrated
that sweeping and leaning the outlet guide vanes reduced
noise without sacrificing aerodynamic performance. The
noise levels recorded for the swept and leaned outlet
guide vanes were typically 3EPNdB than a
conventional design.
The 9x15 Low Speed Wind Tunnel is specially designed
to give researchers a controlled environment in which
to study aircraft engine aerodynamics and acoustics.
Scale-model tests like these help engineers to isolate
noise sources, focus attention where it is most needed,
and develop more effective ways to reduce engine noise.
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