Despite the analysis of muffler performance for many years, most works focus mainly on reducing inlet sound and fail to consider the flow effect. Most of their results correlate well with the experimental measurements. Subsequent works have considered the mean flow effect. Owing to Doppler's effect, transmission loss curve of the muffler will shift in its corresponding frequency. However, the correlation is worse than the experimental results since the flow induced noise does not include in the analysis. This work elucidates how flow induced noise affects muffler performance by analyzing a uniform flow that passes through perforated mufflers. The flow field is calculated with the CFD method, followed by evaluation of the aerodynamic noise based on the simulation results. Additionally, the procedure is simplified by computing and comparing only the total sound power induced by the flow in the muffler interior. Two muffler types, Helmholtz resonator and plug perforated tube muffler, are analyzed and discussed.

The simple expansion chamber muffler is a base control device whose use is to attenuate sound power, and has been known for a long time. Some of the most compelling research has focused on the mufflers with a straight inlet and outlet. To date, a muffler with a right angle inlet has never been studied. Therefore, the purpose of this work is to analyze the simple expansion chamber muffler with a right angle inlet. The numerical results show a comparable agreement between the experiment and other numerical approaches. A discussion is also presented in this work on the muffler with a different radius to that of the inlet/outlet pipe, a different inlet part, etc. The result clearly shows that the attenuation of the muffler with a right angle inlet is better than that with a straight inlet at particular frequencies. In addition, the mufflers do not have any absorbent linings attached to the inside of them, unlike the right angle-inlets which do. However, the propagation of sound in the muffler with a right angle inlet can lead its sound power to be attenuated about 10 ∼ 40dB at those particular frequencies.