| The exhaust from an aircraft engine
is not only loud, it’s hot. While new low noise
engine nozzle designs can and should be tested at cold
conditions first, the most promising nozzles must eventually
be tested with hot gas flowing through them.
Unfortunately, the equipment needed to safely operate
a hot jet acoustic test rig is often very expensive,
which is why you won’t find many such facilities
at universities. NASA Glenn’s Small Hot Jet
Acoustic Rig (SHJAR, pronounced “shar”)
gives researchers nationwide a place to run high-quality
acoustic experiments of heated jets.
SHJAR is one of three rigs installed inside the
anechoic dome of the Aeroacoustic Propulsion Lab.
It can be used to test single stream nozzles up to
5 cm in diameter, Mach 2.0 and 800 K. Researchers
at NASA Glenn have been using SHJAR to develop advanced
measurement techniques like Rayleigh Scattering and
Particle Image Velocimetry. These techniques hold
the promise of unlocking some of the mysteries of
how the turbulence caused by the nozzle creates noise.
The data from this rig is used to validate the computer
codes that are being developed to calculate jet noise.
Better noise prediction codes will help engineers
design quieter nozzles.
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