Frequency-domain nonlinearity analysis of noise from a high-performance jet aircraft

Characterization of far-field jet noise spectral evolution can be performed locally with a single microphone measurement using a gain factor that stems from the ensemble-averaged, frequency-domain version of the generalized Burgers equation. The factor quantifies the nonlinear change in the sound pressure level spectrum over distance [B. O. Reichman et al., J. Acoust. Soc. Am. 139, 2505-2513 (2016)]. Here, noise waveforms from a high-performance military jet aircraft are characterized with this gain factor and compared to propagation losses from geometric spreading and atmospheric absorption. Far-field results show that the high-frequency nonlinear gains at high frequencies tend to balance the absorption losses, thus establishing the characteristic spectral slope present in shock-containing noise. Differences as a function of angle, distance, and engine condition are explored.