Acoustic characteristics of circular dissipative reversing chamber mufflers

In this work, a three-dimensional analytical model is presented for the propagation of sound in circular dissipative reversing chamber mufflers with perforated frontal plates and bulk-reacting fibrous material. The procedure is based on the mode matching method that couples the acoustic pressure and particle velocity at each geometrical discontinuity, and includes the presence of axisymmetric as well as asymmetric modes in the air regions and also within the absorbent material. The complex characteristic impedance and wavenumber are taken into account to model the sound propagation in the bulk-reacting fibrous material. To validate the procedure, the analytical muffler transmission loss predictions are compared with finite element results, showing a good agreement. A detailed study is then performed to assess the acoustical effect of the resistivity of the absorbent material, the porosity of the perforated plates and the main geometrical parameters, such as the location of inlet/outlet ducts, the thickness of the dissipative region and its axial location.