title: Sound radiation from a flanged inclined duct.
abstract: A simple method to calculate sound radiation from a flanged inclined duct is presented. An inclined annular duct is terminated by a rigid vertical plane. The duct termination is representative of a scarfed exit. The concept of a scarfed duct has been examined in turbofan aero-engines as a means to, potentially, shield a portion of the radiated sound from being transmitted directly to the ground. The sound field inside the annular duct is expressed in terms of spinning modes. Exterior to the duct, the radiated sound field owing to each mode can be expressed in terms of its directivity pattern, which is found by evaluating an appropriate form of Rayleigh's integral. The asymmetry is shown to affect the amplitude of the principal lobe of the directivity pattern, and to alter the proportion of the sound power radiated up or down. The methodology detailed in this article provides a simple engineering approach to investigate the sound radiation for a three-dimensional problem.
authors.affiliation: Institute of Sound and Vibration Research, University of Southampton, Southampton SO17 1BJ, United Kingdom. am@isvr.soton.ac.uk
authors.forename: Alan
authors.initials: A
authors.lastname: McAlpine
authors.forename: Alex P
authors.initials: AP
authors.lastname: Daymond-King
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Kempton
mesh_terms: D000162:Acoustics / Q000295:instrumentation*; D003198:Computer Simulation; D004738:Engineering / Q000295:instrumentation*; D004867:Equipment Design; D008962:Models, Theoretical; D009038:Motion; D009716:Numerical Analysis, Computer-Assisted; D011312:Pressure; D012815:Signal Processing, Computer-Assisted; D013016:Sound; D013997:Time Factors