• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.10
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• pp.994-1002
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• 2012

Acoustic power transmission loss(TL) is an important performance of the muffler system. TL will be affected by the velocity of the fluid in duct since acoustic pressure varies according to the fluid velocity. In this paper, two kinds of fluid model, potential flow and turbulent flow, for the fluid flowing in simple expansion chamber are considered. The effects of their two fluid models in acoustic TL are investigated for the straight and L-shaped simple expansion chamber. In higher frequency range, the characteristics of TL of the two fluid models show different results. The variation of TL according to the fluid velocity is shown more distinctly when turbulence model is used. Turbulent flow model should be used to obtain better estimation of acoustic TL in higher frequency range.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.2
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• pp.79-84
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• 2009

Turbocharger has been widely used in many passenger cars in application with diesel engines because of high power and fuel efficiency. However, flow-induced noise (whoosh or hissing noise) which is generated within a compressor during its operation at marginal surge line can deteriorate noise characteristics. Hissing noise excitation is associated with the generation of turbulence within the turbocharger compressor and radiated through the transmission path in a turbocharger system. In this study, a expansion muffler with lids is devised and installed in the transmission path to reduce the hissing noise. Acoustic and fluid dynamic characteristics for the muffler are investigated which are related to the unsteadiness of turbulence and pressure in the turbocharger system. A transfer matrix method is used to analyze the transmission loss of the muffler. A simple expansion muffler with lids is proposed for the reduction of high frequency component noise. Turbulence simulation is carried out by a standard k - ${\varepsilon}$ model. An optimal design condition of the muffler is obtained by extensive acoustic and fluid dynamic analysis on the engine dynamometer with anechoic chamber. A significant reduction of the hissing noise is achieved at the optimal design of the muffler as compared with the conventional muffler.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.11
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• pp.883-889
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• 2014

Mufflers have been widely used in the exhaust system to reduce the noise. However, installing muffler may deteriorate the efficiency due to the increase of back pressure. Mufflers usually consist of partition plates and perforated holes in a expansion chamber. In this paper, the influences of the location of the partition and hole on the acoustic TL and back pressure were examined. The acoustic TL was predicted using virtual lab commercial software, while the back pressure were predicted using CFX commercial software. The results were used to set up a database for finding their trends. The optimal muffler model in user-interested frequency range could be selected by analyzing this database.

• Journal of KSNVE
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• v.9 no.2
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• pp.340-347
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• 1999

The acoustic performance of reactive type single expansion chamber can be calculated theoretically by plane wave theory. But higher order model should be considered to widen the frequency range. Mode matching method has been developed to consider higher order modes, but very complicated algebra should be used. Munjal suggested a numerical collocation method, which can overcome the shortcomings of mode matching method, using the compatibility conditions for acoustic pressure and particle velocity at the junctions of area discontinuities. But the restriction of Munjal's method is that the ratio between the area of inlet(or outlet) pipe and that of chamber must be natural number. In this paper, the new method was suggested to overcome the shortcomings of Munjal's method. The predictions by this method was also compared with those by the finite element method and Munjal's method in order to demonstrate the accuracy of the modified method presented here.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1314-1322
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• 2000

The acoustic property of reactive type single expansion chamber can be analyzed by traditional plane wave theory. This theory can be applied in low frequency range and has good performance. But this theory can't include higher order modes, therefore another method is essential to analyze acoustic filter in high frequency range. Many researcher suggested the method that can concern higher order modes, and their methods are using mode matching technique. But there is no method that can be applied to the analysis of single expansion chamber with arbitrary inlet/outlet duct position and numbers of higher order modes of inlet/outlet duct and middle chamber. In this paper, the method which can analyze single expansion chamber with arbitrary inlet/outlet duct position and numbers of higher order modes of inlet/outlet duct and middle chamber using fundamental mode matching technique, was suggested and the predictions by this method was compared with those by the finite element method, and the influence of inlet/outlet location to acoustic performance of single expansion chamber is investigated and explained by higher order mode effects.

• Journal of KSNVE
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• v.9 no.5
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• pp.914-921
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• 1999

There are many theoretical investigations to analyze higher order mode of reactive type single expansion chambers with offset inlet/outlet locations. But the conventional method has the restriction that the ratio between the area of inlet(or outlet) pipe and that of chamber must be natural number. In the paper, a new method was suggested to apply the Kim's method to silencer with circular cross-section. Not only the offset location but also the magnitude of cross-section area of inlet/outlet pipe can be considered by the suggested method. The predictions by this new method also compared with those by the finite element method and Munjal's method in order to verify the accuracy of the suggested method presented here.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1354-1359
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• 2007

This paper discusses the acoustic performance of simple expansion chamber using computational fluid dynamics(CFD). The CFD model consists of an axisymmetric grid with a single period sinusoid of acceptable amplitude and duration imposed at the inlet boundary condition. The time history of the static pressure is recorded at two points, one in the inlet pipe and one point in outlet pipe. The time history of the static pressure is converted to the frequency domain using Fourier Transform and the transmission loss (TL) of the muffler is obtained from the ratio of the static pressure at the inlet and outlet pipe. The transmission loss of CFD result is compared with that of the computational acoustic analysis using the boundary element method (BEM). There are some differences in two results due to the pressure drop according to the inlet and outlet pipe length. Therefore, the effects of the pressure drop to the transmission loss have to be considered.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2913-2917
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• 2007

Turbocharger has been widely used in many passenger cars in application with diesel engines because of high power and fuel efficiency. However, flow-induced noise (whoosh or hissing noise) which is generated within the compressor during its operation at marginal surge line can deteriorate noise characteristics. Hissing noise excitation was associated with the generation of turbulence within the turbocharger compressor and radiated through the transmission path in turbocharger system. In this study, a sharp-edged reactive-type muffler was devised and installed in the transmission path to reduce the hissing noise. Acoustic and fluid dynamic characteristics for the muffler were investigated which is related to the unsteadiness of turbulence and pressure in turbocharger system. A transfer matrix method was used to analyze the transmission loss of the muffler. Simple expansion muffler with extended tube of the reactive type is proposed for the reduction of high frequency component noise. Turbulence computation was carried out by a standard ${\kappa}-{\varepsilon}$ model. An optimal design condition of the muffler was obtained by extensive acoustic and fluid dynamic analysis on the engine dynamometer with anechoic chamber. A significant reduction of the hissing noise was achieved at the optimal design of the muffler as compared with the conventional turbocharger system.

• Journal of KSNVE
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• v.10 no.1
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• pp.33-40
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• 2000

With the increased requirement for automobile noise, a design fo mufflers with higher performances becomes more important in recent days. For a design of some mufflers, it must satisfy both minimizing back pressure and maximizing sound attenuation in broad range of frequecny. Even for a simple Helmholtz resonator, an important element in a muffler, a resonator design with accurate resonant frequency is difficult if one want to consider standing waves within the cavity. In this paper, the genetic algorithm, one of the optimization technique with high capability of global fittest solution and robust convergence, is applied to the design process of mufflers. Results show that the genetic algorithm can be successfully and efficiently used to find the fittest model for both mufflers and Helmoltz resonators.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.1
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• pp.13-19
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• 1995

The objective of this study is do obtain the relationship between the acoustic mode and cavity tone induced in a perforated tube exhaust muffler. First, the modal frequency for the axisymmetric radial mode and the mode shape have been computed using the impedance model for the perforated tube. Then, experiment has been perfonned for the onset frequencies of the cavity tone for various design parameters and through-flow. The theoretically obtained modal frequencies are well consistent with the measured onset frequencies of the cavity tone, showing that the cavity tone is induced by the axisymmetric radial mode. And it is found that the modal frequency of a perforated tube muffler is much lower than that of a simple expansion chamber.