Transmission Loss Of Muffler Research Articles

Numerical Assessment of Optimal One-Chamber Perforated Mufflers by Using GA Method

Research on new techniques of perforated silencers has been addressed; however, the research work in shape optimization for a volume-constrained silencer requested upon the demands of operation and maintenance inside a constrained machine room is rare. Therefore, the main purpose of this paper is not only to analyze the sound transmission loss of a one-chamber perforated muffler but also to optimize the best design shape under space-constrained conditions. In this paper, both the generalized decoupling technique and plane wave theory are used. The four-pole system matrix used to evaluate acoustic performance is also deduced in conjunction with a genetic algorithm (GA); moreover, numerical cases of sound elimination with respect to pure tones (150, 550, 950 Hz) are fully discussed. Before GA operation can be carried out, the accuracy of the mathematical model has to be checked using Crocker’s experimental data. The results reveal that the maximum value of sound transmission loss (STL) can be optimally and precisely achieved at the desired frequencies. Consequently, the approach used for the optimal design of the one-chamber perforated mufflers is indeed easy and quite effective.

Sound attenuation of a circular multi-chamber hybrid muffler

The sound attenuation of perforated dissipative circular mufflers including a folded resonator and a short expansion chamber is investigated in detail by means of a two-dimensional axisymmetrical analytical approach based on the mode matching technique. The acoustical properties of the bulk reacting porous material and the perforated screen are taken into account to obtain the governing eigenequation for the wave propagation through the absorbent material and central perforated passage. Once the solution of the transverse eigenproblem is computed in all regions, the muffler transmission loss is determined by matching the acoustic pressure and axial velocity across each geometrical discontinuity. In addition, finite element results and experimental measurements are utilized for validation. The acoustic attenuation performance is examined considering the effect of the internal geometry of the muffler, the properties of the sound absorbent material and the porosity of the perforated pipe. Comparison is also provided with hybrid mufflers of earlier studies. It is shown that the acoustic contribution of the folded resonator is reinforced by the presence of the short expansion chamber, providing a good noise attenuation performance in the low and mid frequency range, whereas the dissipative effects associated with the central chamber suppress the high frequency noise, thus leading to a broadband attenuation of sound energy.

Numerical studies on venting system with multi-chamber perforated mufflers by GA optimization

Research on new techniques of perforated silencers has been well addressed and developed; however, the research work in shape optimization for a volume-constrained silence requested upon the demands of operation and maintenance inside a constrained machine room is rare. Therefore, the main purpose of this paper is to not only analyze the sound transmission loss of a multi-chamber perforated muffler but also to optimize the best design shape under space-constrained condition. In this paper, both the generalized decoupling technique and plane wave theory are used. The four-pole system matrix in evaluating the acoustic performance of sound transmission loss (STL) is also deduced in conjunction with a genetic algorithm (GA). To demonstrate the precision of the tuning ability in a muffler, various targeted pure tones are proposed in numerical cases. Results reveal that the maximal acoustical performance precisely occurred in the desired frequency. Furthermore, a noise reduction with respect to full-band exhausted noise emitted from a diesel engine is also introduced and assessed. To achieve a better optimization in GA, several test parameter values were used. Before a GA operation can be carried out, the accuracy of the mathematical models have to be checked by experimental data. The optimal result in eliminating full-band noise reveals that the overall noise reduction of a multi-chamber muffler can achieve 68 dB under space-constraint conditions. Consequently, the approach used for the optimal design of the STL proposed in this study is indeed easy, economical and quite effective.

Evaluation of transmission loss using the boundary element method for mufflers with two inlets

Mufflers with multiple inlets and multiple outlets are commonly used in exhaust systems which provide the benefits of lower restriction and higher engine performance. In this paper, the direct mixed-body boundary element method (BEM) is used to predict the transmission loss (TL) of mufflers with two inlets and one or two outlets. To do this, the impedance matrix of the muffler is first computed by the BEM. The transmission loss (TL) can then be evaluated from the impedance matrix which relates the sound pressure at the inlets and the outlets to their corresponding normal particle velocities. A complex-number ratio of the sound pressure at the second inlet to the sound pressure at the first inlet will need to be supplied before the TL can be evaluated. However, the exact value of this ratio may not be known a priori in real applications, let alone the ratio would be a function of frequency. Therefore, an estimate has to be made and the TL needs to be presented with different possible values of the ratio. Numerical test cases are given in the paper, and results are verified by comparing to the five-point method and the six-point method.

Modeling and applications of partially perforated intruding tube mufflers

In this study, a new approach is presented for modeling concentric partially perforated intruding tube mufflers. For acoustic impedance in the linear regime, a closed form solution of the partially perforated intruding tube muffler transmission loss was first obtained. With this restriction and in the case of zero mean flow, excellent agreement between predicted and experimental results for various muffler configurations demonstrates the utility and potential of the modeling approach used in the present study. By tuning the lengths and associated physical parameters to the in-situ case of various straight-through tubular elements, one can achieve rapid and economical modeling of those that are frequently used in many commercial reactive mufflers. This modeling ability is very useful to a muffler designer especially in the preliminary design stage.

A study on the transmission loss of straight‐through type reactive mufflers

Abstract The following study presents a newly developed approach for modeling perforated muffler components, such as partially perforated extended inlet/outlet elements. After evaluating the transfer matrices of all sub‐elements, the transfer matrices product is obtained by multiplication of partially perforated extended inlet/outlet elements. For acoustic impedance in the linear regime, a closed form solution of the partially perforated intruding tube muffler transmission loss was first obtained. In the case of zero mean flow, the predicted results for the various muffler configurations strongly corresponds to the measured values within the limitations of the one‐dimensional theory. By tuning the lengths and associated physical parameters to the in‐situ case of various tubular elements, one can achieve rapid and economical modeling of frequently used commercial reactive mufflers as well as mufflers for other industrial applications can be achieved. This aeroacoustic modeling ability is very useful for vehicular muffler designer especiallly during the preliminary design stages.

The transmission loss of double expansion chamber mufflers with unequal size chambers

The double expansion chamber muffler is a commonly used silencing element in duct noise applications. The transmission loss for the case of equal size chambers is known and easily calculated. A closed form expression for the transmission loss for the case of chambers of unequal length and area is presented here. It is also shown that significant tuning benefits result with chambers of unequal size. For evenness of response, with a minimum passband, chamber length ratios of 2:1 and connecting tube lengths equal to the shortest chamber are superior.

Measured performance and predicted transmission loss of plug mufflers

Predicted transmission loss characteristics of plug mufflers are compared to measurements of both transmission loss and insertion loss. A plug muffler is a cross flow expansion and a cross flow contraction perforated tube element connected in series. The predictions were based on transfer matrix calculations using a decoupling approach which gives closed form expressions for the matrix terms [K. Jayaraman and K. Yam, J. Acoust. Soc. Am. 69, 390–396 (1981)]. Transmission loss measurements with and without flow were made on an impedance tube with a horn‐driver as a noise source. Insertion loss measurements were made on the impedance tube, a cold flow facility, and on an engine. Results (zero) are shown for Mach numbers from 0–0.18 at ambient and elevated temperatures. The agreement between the measured and predicted results is excellent.

A finite element method for damped acoustic systems: An application to evaluate the performance of reactive mufflers

The approximate equations governing the forced harmonic motion of a damped acoustic system are set up by using a variational principle. Acoustic finite elements are then used in a computer program to study the transmission loss and insertion loss performance of some expansion chamber mufflers. The manner in which the equations are set up allows a number of input and output nodes, and two-dimensional effects involving the influence of transverse acoustic modes to be taken into account. Although only the simplest of elements and coarse mesh sizes are used the resulting accuracy of the solutions is extremely good; thus the method should be a viable one for studying the performance of more complicated mufflers, having variable cross-sections and internal energy dissipation.

Standing waves in the presence of a temperature gradient

In many practical problems such as those involving the measurement of the impedance of materials and of the transmission loss of mufflers, it is necessary to measure standing waves. Temperature gradients in the fluid can complicate the analysis problem. The standing-wave equation is derived for the case of standing waves in the presence of a linear temperature gradient. A closed-form solution is developed and the shape of the standing waves are shown for arbitrary test eases. A numerical technique is also developed as an alternate solution consisting of a discrete element approximation. The results of each type of solution are compared using the test cases.