Sound transmission through micro-perforated double-walled cylindrical shells lined with porous material

Abstract

Sound transmission through a double-walled cylindrical shell with porous cores and the inner shell micro-perforated is studied analytically in this paper. The Donnell's thin shell theory is used to govern shell motions and the Biot's theory is applied to describe sound propagation in the porous layer. Boundary condition at the perforated shell is presented by the mean particle velocity model. When excited by an oblique plane wave with external mean flow, transmission losses through typical configurations are numerically computed. Results show that perforating the inner shell of different sandwich configurations would produce improvement of transmission loss below the ring frequency. In further analysis regarding the perforated configuration with two airgaps in annular space, it retains superiority against the corresponding non-perforated one in the low frequency range despite alteration of the incidence angle, the azimuthal angle or the external flow. In parametrical studies, increase of either the aperture diameter or the perforation ratio is validated to enhance low-frequency sound insulation of this configuration through the imaginary part of the impedance constant.