Exhaust jet noise reduction is due to the impact on the flow of gas changing its direction, temperature, density, creating obstacles, but unfortunately all of these activities increase the power loss.

In fact there is no such reliable methods of calculation, mufflers simply chosen from a number of models, respectively, more effective and established a real product.

Petr thanks for your answer and time, but what makes me wonder is there are many commercial 1-D codes available in market to do all these calcualations like Ricardo Wave and GT- power, i was kind of thinking what all equations they use of a simplied but reliable results. I guess they might use Transfer Matrix Method. Do you have any insights on these commercial tools or TMM ? if yes, please give your opinion.

Hello Sidharath! Usually, in silencer simulations, the easiest approach is based on the 1-D linear equations (continuity and momentum) under the assumption of isoentropic process and harmonic time dependence of all the variables. Under these hypotheses the above equations can be """easily""" (!) solved in each part constituting the silencer, and eventually they can by combined by using a product between the transfer matrices of the elements. The TM of the entire muffler is given by the product of the TMs of all the components, and the Transmission loss of the muffler can be expressed as a function of the global TM (at each frequency).

I'm not very sure about Ricardo Wave but GT-Power allows to perform linear-calculations. Anyways, the most used acoustic tool of GT-Power is the one based on non-linear equations solved through a time domain approach. The equations are no more linear and there's no more harmonic dependence of the variables. So the complexity in that case is higher, but the program can exploit the time-domain formulation used for the fluid-dynamic simulations of the manifolds (which is he main goal of the software).

GT-power also uses some "hybrid" 0D-1D elements (flow splits) to fill the expansion chambers. My suggestion is: pay attention when you simulate short chambers with big diameters.....

In conclusion, if you want to program a little tool to simulate simple silencer configurations, then you should definitely use the 1D linear approach. One of the best gurus in this field is Munjal, and his book is a sort of Bible for the acousticians (no offense for the other guys)! Good luck and let us know about your simulations!

Hi Fabio...thanks a lot for your input...am currently using the same very approach of Transfer Matrix Method, to split the whole muffler into smaller area applying continuety and momentum transfer equations and product of [ T ] to get the get global TL, its just an having some problems on how to split and implicating 1-d equations but am working on it, using Dr. Mujal's notes.

PS. I've met Prof Munjal in person on many occasions, he is teaching in IISc Banglore and getting to learn from him.

Once again thanks for your input

Good day.

HI Sidharath,  the effect of perforated baffles can be taken into account by the newly developed method called the "Integrated Transfer Matrix Method (ITMM)" developed by Vijayasaree and Munjal which makes use of the empirical relations for the acoustic impedance of perforates. For details on the methodology, kindly refer to https://www.researchgate.net/publication/256800314_On_an_Integrated_Transfer_Matrix_method_for_multiply_connected_mufflers

This technique is also available in the second edition of the Acoustics of Ducts and Mufflers.

I have used this method extensively for my Master's dissertation. 

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