MODELING OF FLUID MACHINES AS SOURCES OF SOUND IN DUCT AND PIPE SYSTEMS

This article presents a review on the modelling of fluid machines as s ources of fluid-borne sound. Source models are necessary to calculate the interaction between a source and its surrounding; this interaction will among other things determine the sound power emitted by the sour ce. Accurate source models are therefore important when trying to find efficient noise control solutions. This is especially true as long as the size of an acoustic problem measured in wavelengths (the Helmholt z number) is of the order one or less. In this low- or mid-frequency r egion large errors can result from characterizing a source simply by t he acoustic power it generates in a specified surrounding (e.g., refle ction-free). Methods based on this type of approach are described in t he international standards which treat the testing of acoustic sources . Alternative methods valid in the low or mid-frequency region are des cribed in this article. Although the article focuses on the modelling of fluid-borne sound sources, it should be noted that most of the idea s are applicable also to describe structure-borne sound sources.