Three-Dimensional Numerical Study on the Pulsating Flow Inside Automotive Muffler with Complicated Flow Path

Exhaust system is composed of several parts. Among them, design of muffler system strongly influences on engine efficiency and noise reduction. Hence, thorough comprehension of flow characteristics inside muffler is necessary. In this study, three-dimensional steady and unsteady compressible flow analysis was performed to understand the flow characteristics, pressure loss and amplitude variation of pulsating pressure. The computational grid generation was carried out. And the three-dimensional fluid motion inside the muffler was analyzed by STAR-CD, the computational fluid dynamics code. RNG k- ε turbulence model was applied to consider the complexity of the geometry and fluid motion. The steady and unsteady flow field inside muffler such as velocity distribution, pulsating pressure and pressure loss was examined. In case of unsteady state analysis, velocity of inlet region was converted from measured pulsating pressure. Experimental measurement of pressure and temperature was carried out to provide the boundary and initial condition for computational study under the engine operating conditions. Computational results show that the pressure drop is derived from the sudden reduction and the sudden expansion effect of the baffle plates, located in the middle of chamber, and heavily depends on the variation of the flow direction. It is also found in good agreement within 6% of the measured values.