Abstract
Noise measuring tests of a low-bypass-ratio turbofan engine were conducted, using the hybrid bulk-resonator type acoustic treatment in the fan section and the lobe type internal mixer in the exhaust section.The bulk-resonator type acoustic treatment is composed with a thin layer of polyamid fiber felt protected by the perforated sheet metal on its surface and backed by an air cavity behind the felt layer. Test results revealed that this kind of acoustic treatment was effective for reduction of fan noise thru broad frequency rang from approach to take-off power, and the mixing nozzle was effective for jet noise reduction in high power range with a slight thrust loss which was not considered to be caused only by installation of the mixing nozzle.
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