Sound attenuation in partially-filled perforated dissipative mufflers with extended inlet/outlet

The current study considers the acoustic characteristics of partially-filled perforated dissipative circular mufflers with extended inlet/outlet. In addition to the finite element method (FEM), a two-dimensional (2-D) axisymmetric analytical approach is developed that matches the acoustic field across the discontinuities by applying the continuity conditions of the acoustic pressure and velocity. The complex characteristic impedance, wavenumber and perforation impedance are taken into account to evaluate the axial wavenumber in the absorbing fiber and in the central perforated pipe. In addition, experimental work is considered for validation purposes. Several effects regarding the extended inlet/outlet ducts and the fiber properties are presented and discussed