Application of event-based beamforming to the study of acoustic shocks in installed supersonic engine noise

Crackle is a dominant component of the noise from supersonic military-style jet engines. Because the study of crackle is tied to the characterization of acoustic shocks, examination of the locations and propagation direction of the largest-derivative waveform events in the near field can provide insights regarding source radiation and propagation characteristics. This paper describes initial results of applying an event-based beamforming algorithm to a ground-based microphone array located in the near-field of a T-7A Red Hawk aircraft with its afterburner-capable F-404 engine. The work builds on recent work by Vaughn et al. [AIAA Paper 2019-2664]; the algorithm identifies large-derivative events at pairs of adjacent microphones and determines the propagation direction by applying a cross correlation to short time segments around the events. Statistical analysis of these events, and associated beamforming, for the T-7A noise radiation leads to an improved understanding of the noise radiation of temporal events tied to acoustic shocks and, therefore, to crackle. [Work supported by AFRL.]