Because phenomena observed in noise radiated from high-performance military aircraft are not fully understood, different analysis techniques can yield complementary insights into their characteristics. Here, a coherence analysis from a 120-microphone near-field array is used to identify and characterize the noise radiation and source-related properties of a T-7A-installed F-404-GE-103 engine over a broad range of frequencies. Some of the noteworthy findings include: a) coherence trends for mixing noise and spatiospectral lobes generally match those observed for previously studied aircraft; and b) bands of coherence between upstream and downstream locations are observed at higher engine powers, suggesting a coherent interaction between upstream broadband shock-associated noise radiation and downstream Mach wave radiation. [Work supported by ONR Grant No. N00014-21-1-2069.]

Spatiospectral lobes are features identified in the noise fields surrounding full-scale tactical aircraft that are unseen in most lab-scale experiments. Prior studies have explored their characteristics in the frequency domain, but a joint time-frequency domain (JTFD) analysis has potential to further explore these phenomena and connect them to source-related events. This paper applies the event-based beamforming technique developed by Vaughn et al. [AIAA J. 2021] to acoustical data collected at a 120-microphone array near a T-7A-installed F404 engine. The algorithm correlates time-domain events between pairs of adjacent microphones to find an event propagation direction and then ray traces to the jet nozzle lipline to identify an apparent source location. In addition to the large-derivative events used previously to identify crackle-related phenomena, this paper uses a JTFD wavelet analysis to expand the possible triggers to extract physical insights into the lobes. The lobe directivities are explored and compared to frequency-domain studies. [Work supported by Grant No. N00014-21-1-2069.]

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