Influence of Liner Thickness, Mean Flow Profile, and Three-Dimensionality of Duct on Sound Wave Propagations in Lined Ducts
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This paper concerns propagation and attenuation of sound waves through acoustically lined ducts. For a cylindrical duct whose linear consists of a point-reacting porous layer backed by cellular cavities, the admittance formula derived by taking into account a wave motion within the liner is applied to an analysis of wave propagation downstream and upstream. Attenuation spectra evaluated by this analysis are compared with those based upon the semi-empirical formula widely used. For the point-reacting liner of fixed porous material properties, influences of the liner thickness, mean flow profile, and three-dimensionality of duct (i.e. cylindrical or plane) on the attenuation of waves propagating both downstream and upstream are examined. Moreover, the attenuation of waves with several spinning modes is examined for the case of uniform mean flow. The results show a significant role of the porous layer thickness for the attenuation characteristics of wave propagations.
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