Decomposition of military jet aircraft mixing noise into fine and large-scale turbulent components

Abstract

Many far-field measurements of laboratory-scale jet noise have shown good agreement with the two similarity spectra developed to represent the contributions of fine-scale and large-scale turbulent structures [Tam et al., AIAA paper 96-1716, 1996]. Measurements near an F-22A Raptor provide a means to study how accurately the similarity spectra describe the noise from a full-scale, high-performance, jet engine. Comparisons have been made using ground-based microphones at 60° to 150° for three engine conditions: intermediate, military and afterburner, with more detailed analyses than described previously [Neilsen et al., J. Acoust. Soc. Am. 129, 2242 (2011) ]. The good agreement with Tam’s predictions - the fine-scale spectrum at upstream and sideline angles and the large-scale spectrum in the maximum radiation direction - permits a quantitative analysis of the contributions of the two spectra at other angles. The radiated spectra and overall levels for all three engine conditions have been decomposed into contributions from the two spectra as functions of angle. Of particular interest is the appreciable contribution of fine-scale turbulence aft of the maximum radiation directions at military and afterburner conditions. [Work sponsored by the Office of Naval Research.]