Design and analysis of a novel muffler for wide-band transmission loss, low back pressure and reduced flow-induced noise

With the advancements in quiet engine technology, reduction of the fan noise sources, and use of higher mean flow speeds, the aerodynamic noise generation due to unsteady and turbulent mean flow in the ducts of automotive exhaust muffler may become a significant source of exhaust noise, thereby limiting the net insertion loss of the muffler. Three-pass double-reversal muffler is often used in automotive exhaust systems. This muffler is characterized by a fairly wideband transmission loss (TL) curve as well as relatively low back pressure. However in the flow-reversal end chambers, it produces a lot of aerodynamic noise due to impingement of jets on the end plates, generation of free shear layer and vortex shedding. This paper deals with the design and analysis of the muffler with a novel feature (tubular bridges in the end-chambers) specially configured to minimize the free shear layer in the end chambers of the three-pass doubler eversal muffler as well as to provide adequate acoustic transmission loss and to further reduce the back pressure of the muffler. The TL curve predicted by means of the 1-D integrated transfer matrix (ITM) approach is validated against the 3-D FEM and compared with that of the base muffler (without tubular bridges). Back pressure of the configuration with tubular bridges, estimated by means of the lumped flow-resistance network, is shown to be considerably less than that of the base muffler.