SOUND PROPAGATION IN CIRCULAR DUCTS LINED WITH NOISE CONTROL FOAMS

Finite element predictions and corresponding measurements for sound attenuation and phase speed in a circular duct lined with poroelastic noise control foams are presented in this article. In the present study, four configurations having different lining thickness are considered for three types of foam samples. An axisymmetric foam finite element formulation based on Biotʹs theory is presented. The macroscopic physical properties of the foam lining samples were estimated using an optimization procedure based on measured physical and acoustical data. The results are also compared with Morseʹs local reaction solutions. The effects of lining thickness and foam properties on the sound attenuation are illustrated. Finally, by comparing measurements for thick and thin linings with predictions made using constrained and lubricated boundary conditions it is demonstrated that the manner in which lining materials are fitted into ducts can affect the sound attenuation.