| Short duration tests had indicated
fan noise could be reduced by blowing air through the
trailing edge of the rotor blades. But it was clear that
longer and more detailed tests in a continuous flow facility
were needed. Hollow fan blades were constructed and installed
in the Advanced Noise Control Fan Rig.
Both aerodynamic and acoustic measurements were taken
since the goal was to reduce noise without sacrificing
fan performance. Being able to readily change test
parameters, and having access to special instrumentation
like the Rotating Microphone Rake enabled engineers
to study the problem more closely.
Not only do we now know that far field sound power
levels can be reduced by as much as 10-12 dB using
trailing edge blowing, but we also have learned a bit
about why this is possible. Sharing what we’ve
learned about the physics of noise helps whole industries
to use and optimize these techniques for their products.
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