Sound propagation attenuation in lined annular-variable area ducts using bulk-reacting liners

The sound propagation through the annular lined variable-area ducts is controlled by the design parameters of the duct liner. The bulk-reacting liners are liners that permit propagation of sound in more than one direction. This research presents the solution of the three-dimensional complex partial differential equations of the sound wave propagation in the duct, using the method of multiple scales. The effect of liner design parameters such as, duct liner length, duct outer diameter, liner thickness, resistivity, and porosity of porous material on sound attenuation has been computed by a special computer program. The results show that the attenuation of sound is directly proportional to the liner length, liner thickness and porosity to some extent, and inversely proportional to liner resistivity and duct area.