| Imagine sitting on one of Lake
Erie’s dock’s on a sunny summer day when
you see a jet-skier speed away. Not long afterwards,
waves from the wake of the jet-ski lap upon the dock.
Now, imagine you are sitting on a stator vane downstream
of a turbofan rotor. As air passes through, wakes from
the rotor hit the stator. Unlike the pleasant sound
of Lake Erie’s waves, rotor wakes hitting turbofan
stators create loud and annoying broadband and tone
noise.
Rotor/stator interaction noise is the engineering
term used to describe noise created this way and is
one of many ways that air passing through an engine
makes noise. Since we cannot see wakes in an airstream
like we can see wakes in water, we must use special
instrumentation like hotwire probes and Laser Doppler
Velocimeters (LDV) to measure the air velocity between
the rotor and the stator. Plots of the velocity measurements
can be made which allow us to “see” the
disturbances that the rotor created.
Since periodic disturbances results in tone noise
and random turbulence generates broadband noise, detailed
velocity measurements play an important role in identifying
noise sources. Hotwire and LDV data are routinely used
to validate calculations used to estimate noise from
turbofan engines.
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