Intensity analysis of peak-frequency region in noise produced by a military jet aircraft

Acoustic intensity measurements of the F-22A Raptor are analyzed as part of ongoing efforts to characterize the noise radiation from military jet aircraft. Data were recorded from a rig of microphones and an attached tetrahedral intensity probe at various locations to the sideline and aft of the aircraft. Recently, techniques such as coherence, similarity spectra analyses, and near-field acoustical holography have indicated a peak-frequency region comprised of two maxima that have very different radiation directionalities. Acoustic vector intensity is analyzed as a function of frequency to further assess the behavior of this double-peak phenomenon, which is not accounted for by current jet noise models. The results thus far confirm the discrete nature of the peaks and their directionalities.