“Buzz-saw” noise: A comparison of modal measurements with an improved prediction method

“Buzz-saw” noise is radiated from a turbofan inlet duct when the fan tip speed is supersonic. In a recent article the effect of an acoustic liner on buzz-saw noise has been examined. Spectral measurements in a rigid and an acoustically lined inlet duct have been compared. Also these measurements have been utilized to assess a buzz-saw noise prediction method. The prediction method is based on a one-dimensional nonlinear propagation model. Sound absorption by an acoustic lining can be included in the model. In this article, the buzz-saw noise prediction method is improved by the inclusion in the modelling of the effect of a boundary layer on absorption of sound in a lined duct. Also, modal measurements from a circumferential microphone array have been examined. These show that the principal source of buzz-saw noise is not always the rotor-alone pressure field. Non-rotor-alone scattered tones can be a significant source of buzz-saw noise at low supersonic fan speeds. The numerical simulations, which only predict the rotor-alone tones, have been re-evaluated in light of these new modal measurements.

[1]  Walter Eversman,et al.  Effect of Boundary Layer on the Transmission and Attenuation of Sound in an Acoustically Treated Circular Duct , 1971 .

[2]  P. Mungur,et al.  Propagation and Attenuation of Sound in a Soft-Walled Annular Duct Containing a Sheared Flow , 1969 .

[3]  Brian J. Tester,et al.  Some aspects of “sound” attenuation in lined ducts containing inviscid mean flows with boundary layers , 1973 .

[4]  Walter Eversman,et al.  Theoretical models for duct acoustic propagation and radiation , 1991 .

[5]  A. H. Nayfeh,et al.  Effect of mean-velocity profile shapes on sound transmission through two-dimensional ducts , 1974 .

[6]  Alan McAlpine,et al.  On the prediction of “buzz-saw” noise in acoustically lined aero-engine inlet ducts , 2003 .

[7]  Brian J. Tester,et al.  The propagation and attenuation of sound in lined ducts containing uniform or “plug” flow , 1973 .

[8]  Sw Sjoerd Rienstra,et al.  A classification of duct modes based on surface waves , 2001 .

[9]  Brian J. Tester,et al.  Supersonic fan tone noise prediction , 1998 .

[10]  D. Pridmore‐Brown,et al.  Sound propagation in a fluid flowing through an attenuating duct , 1958, Journal of Fluid Mechanics.

[11]  Alan McAlpine,et al.  “Buzz-saw” noise: A comparison of measurement with prediction , 2006 .

[12]  T. G. Sofrin,et al.  Axial Flow Compressor Noise Studies , 1962 .

[13]  Alan McAlpine,et al.  ON THE PREDICTION OF “BUZZ-SAW” NOISE IN AERO-ENGINE INLET DUCTS , 2001 .

[14]  Edward Rademaker,et al.  Mode detection with an optimised array in a model turbofan engine intake at varying shaft speeds , 2001 .