吸音ダクトにおける騒音の伝搬とその低減率

概要

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The sound propagating in an acoustically lined duct of an aeroengine is incident to the acoustic treatment with oblique angle of incidence, rather than normal to the surface. Therefore, the frequency band where the largest absorption can be obtained changes from that calculated in the assumption that the sound would propagate perpendicularly against the surface. So the specification of acoustic treatment should be determined in terms of impedance in order to maximize noise attenuation at a certain frequency range. The impedance varies with frequency, kind of modes, main flow Mach number and duct geometries. In this paper, the relation between the impedance of the duct wall and the noise attenuation is analyzed, and acoustic test using a turbofan engine is conducted to evaluate the feasibility of the design technique of acoustic treatment.
1980-12-25