Near-field coherence analysis of noise from an installed F404 engine

Abstract

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.]