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Exhaust and muffler noise is a challenging problem in the transport industry. While the main purpose of the system is to reduce the intensity of the acoustic pulses originating from the engine exhaust valves, the back pressure induced by these systems must be kept to a minimum to guarantee maximum performance of the engine. Emitted noise levels have to ensure comfort of the passengers and must respect community noise regulations. In addition, the exhaust noise plays an important role in the brand image of vehicles, especially with sports car where it must be tuned to be “musical”. However, to achieve such performances, muffler and exhaust designs have become quite complex, often leading to the rise of undesired self-induced noise. Traditional purely acoustic solvers, like Boundary Element Methods (BEM), have been applied quite successfully to achieve the required acoustic tuning.

Automotive exhaust mufflers are not only attenuating noise, but can, in fact, along with other exhaust components, generate noise within the exhaust system. This type of noise is commonly called “flow generated noise” to distinguish it from the “pulsation noise” excited by the combustion engine. Flow generated noise is normally very broad band but it can also have tonal regions. This tonal flow noise can sound like a whistle. In this contribution an experimental study of the generation and prevention of such whistle tones will be presented. The study was focused on perforated pipes in mufflers with different perforation patterns, hole sizes and hole shapes. The noise spectra have been measured on a flow bench at room temperature as well as under real (hot) conditions on a vehicle. The results will be correlated in terms of frequency and Strouhal number. Concepts to avoid or suppress these tones will also be discussed.

This paper describes the application of a “Design of Experiment”-Method (Taguchi-Method) to reduce the tail-pipe noise of an exhaust system. The aim of this work was to find out how effective and useful this method is in developing the acoustic behavior of an exhaust system. For that purpose the Taguchi-Method [1] was applied to three different exhaust systems. Several geometric parameters, such as pipe diameter and length or muffler volume, have been changed at each exhaust system. The time domain engine/exhaust simulation code WAVE was used to calculate the tail-pipe noise. The benefit of Taguchi's Method is, that only a slight number of parameter combinations is necessary to measure, in order to obtain the optimal configuration of a vast number of possible combinations. In addition one gets also the response intensity of each parameter. These informations lead to an optimum combination of the parameters according to the desired target.