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In this paper a unique experimental facility designed for a complete determination of the sound transmission in turbochargers is introduced. The facility can be used to characterize the passive acoustic effect for turbocharger compressors and turbines working in realistic operating conditions by extracting the acoustic two-port data. The acoustic pressure transmission loss results for a passenger car turbocharger compressor and turbine measured in up- and downstream directions regarding the mean flow are presented. The data are obtained for various operating points of the turbocharger and the influence of operating conditions on the sound transmission is discussed.

Non-linear 1-D CFD time domain prediction codes are used to calculate the performance of the gas exchange process for IC-engines. These softwares give time-varying pressures and velocities in the exhaust and intake systems. They could therefore in principle be used to predict radiated orifice noise. However, the accuracy is not sufficient for them to be used as a virtual design tool. More accurate results might be provided by dividing the problem into a source domain and a transmission domain and use linear 3-D frequency domain codes to describe the transmission part. Radiated shell noise and frequency dependent damping could also be included in the frequency domain models. The simplest source model used in the low frequency plane wave range for simulation of dominating engine harmonics is the linear time invariant 1-port model. This acoustic source data is usually obtained from experimental tests where the multi-load methods and especially the two-load method are most commonly used.

Both linear (frequency domain) and non-linear (time domain) prediction codes are used for the simulation of duct acoustics in exhaust systems. Each approach has its own set of advantages and disadvantages. One disadvantage of the linear method is that information about the engine as an acoustic source is needed in order to calculate the insertion loss of mufflers or the level of radiated sound. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. This source characterization data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. These measurements are time consuming and expensive. However, this data can also be extracted from an existing 1-D non-linear CFD code describing the engine gas exchange process.