Nonlinear propagation and shock formation are shown in noise radiated from full-scale military jet aircraft. Perception of sound is not only affected by the overall sound pressure level of the noise, but also characteristics of the sound itself. In the case of jet noise, acoustic shocks within the waveforms result in a characteristic commonly referred to as"crackle." The origin of shocks in the far-field of jet noise is shown to be through nonlinear propagation. Metrics characterizing the shock content of a waveform are explained and given physical significance, then applied to jet noise at various distances and engine conditions to show areas where shock formation is significant. Shocks are shown to develop at different distances from the aircraft, dependent on the amplitude and frequency, and nonlinear propagation is shown to be important in determining time and frequency characteristics of jet noise at distances of up to 1220 m from the aircraft. The shock content is also characterized during flyover experiments, and the shock content between the two scenarios is compared. While some reduction in overall level and shock content is seen in the maximum radiation region, level increases in the forward direction during flight result in increased shock content. Variation at distances of 305 m and beyond is considered and shown as a result of small atmospheric changes. Finally, a nonlinear numerical propagation scheme is used to model the propagation, showing accuracy in predicting frequency-domain and time-domain features that are evidence of nonlinear propagation.



College and Department

Physical and Mathematical Sciences; Physics and Astronomy



Date Submitted


Document Type





jet noise, aeroacoustics, nonlinear propagation, shock, crackle



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Physics Commons