Acoustics of Turbochargers

Noise from turbo-chargers is increasingly becoming an issue. Partly due to improved noise control of other components and partly due to increased specific mass flows. Despite that the turbocharging technique was developed in the first part of the last century the acoustical behavior is still a field where there is a lack of research. In this paper an overview of the existing research is presented including the work done in the EC-project ARTEMIS. Some first results from recently started investigations at the new gas management research centre, KTH CICERO, will also be described. A turbo-unit always consists of a compressor which normally is driven by an exhaust turbine. Both the turbine and the compressor will have an influence on how the low frequency engine pulsations propagate in the intake/exhaust system. This is referred to as the passive acoustic property of the turbo-unit. If linear acoustic models are applied the passive properties can be described using reflection and transmission coefficients. A turbo-unit will also produce high frequency aerodynamic sound, which is referred to as its active ("sound generating") acoustic property. The sound generation is associated with the rotating blade pressures and for modern turbo-units, with supersonic tip speeds, also with rotating shock waves ("buzz-saw noise").

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