On sound power determination in flow ducts

The following problems associated with sound power determination in circula r ducts carrying mean flow are discussed: axial standing waves due to sound reflections from the duct end; acoustic loading of the source; turbulent f low pressures superimposed on the sound field: discrimination between sound pressures and turbulent flow pressures; radial measurement position in the duct in view of higher order mode sound propagation and directional charac teristic of the microphone probe used; modal distribution of sound power. E arly and recent work on the above topics is reviewed. Brief descriptions of the standardized in-duct method ISO 5136:1990 (International Organization for Standardization. Geneva, Switzerland, International Standard) [1] and t he revised measurement procedure ISO/DIS 5136:1999 (International Organizat ion for Standardization, Geneva Switzerland, Layout for a Draft Internation al Standard) [2] are given. (C) 2001 Academic Press.