Abstract
The sound pressure level of flow induced noise from a muffler may become high for particular muffler sizes and flow velocities. This phenomenon is mainly one of resonance as it is related to muffler natural frequencies. Usually, the sound pressure level is much higher in the case when predominance of tail pipe resonance rather than cavity resonance occurs. The predominance of tail pipe resonance intervenes for particular combinations of flow velocities and cavity lengths. The phenomena are considered to be strongly related to vortex ring generation at constant frequency inside the cavity by feedback mechanism from resonance noise to flow. The predominance of tail pipe resonance can be controlled by changing distributions of the flow velocity in the cavity through bellmouth shaped structure mounted at the entrance of the cavity. It can be also controlled through bellmouth shaped structure mounted at the exit of the cavity and/or by using absorbing material that is stuck to the cavity walls, reducing thus the sound pressure level of the tail pipe resonance.
