F2010C067
Simulation Process Development of Radiation Noise and Application on the Exhaust Muffler
(Key Word : Muffler, Radiation Noise, CFD, Structure/Sound Simulation)
Muffler radiation noise is the important noise source that influence vehicle interior NVH performance. So, many car makers have estimated muffler radiation noise by simulating simply structure mode of muffler case in order to understand a robust characteristic of muffler radiation noise until now.
But, radiation is induced by the exhaust flow fluctuations and accompanied by complex interaction between fluid and structure. Especially, flow interactions are very complex because high turbulence and pressure are generated due to the high velocity flow inside of the muffler.
In other words, it is impossible to find optimum dimensions and thickness of muffler components in order to reduce radiation noise if we can not comprehend flow characteristics and fluid-structure interaction inside the muffler as a primary cause of radiation such as pressure fluctuations. And it is difficult to improve cost and weight competitiveness when simply considering stiffness of muffler structure.
So, this study investigates the effect of muffler components such as muffler case, end-plate and baffles on the radiation noise by using computer simulation method which is characterized by linking Computational Fluid Dynamics, structure simulation (NASTRAN) and sound simulation (SYSNOISE) consecutively. In order to link CFD with the structure simulation programs, data converting code between time-domain pressure data as CFD results and structure simulation input data were programmed and employed in this study.
Muffler radiation measurements are also conducted in order to confirm the reliability of simulation method. The experiments are carried out in the engine dynamometer and microphone is located 100mm away from the muffler.
As a result, various radiation noise level were observed according to design parameters of muffler components and we could identify the effect of thickness of muffler component, length of muffler inner pipe, and location of inner baffle on the radiation noise of muffler.
The results are summarized as follows: 1) The radiation noise of exhaust muffler measured in the engine dynamometer is in a good agreement with the numerical predictions result. 2) Thicknesses of case-outer and end plate-in/out panels are dominant factors which influence radiation noise level of muffler. On the other hand, thicknesses of baffle and case-inner/center panels don't affect radiation noise. 3) Change of location of baffle also has a large effect on the radiation noise level of muffler. 4) By selection of appropriate parameters of muffler components showing lower radiation noise levels, we could design the muffler having lower radiation noise and competitive cost/weight.
This abstract is supplemented by a PDF, which can be viewed here.