On Broadband Shock-Associated Noise Source and Radiation Characteristics From an Installed, Afterburning GE F404 Engine

Broadband shock-associated noise (BSN) is a major source of high-frequency noise in imperfectly expanded supersonic jets. While BSN has been extensively studied, source characterization from full-scale engines remains limited. This paper investigates BSN source and radiation characteristics from a full-scale, installed GE F404 engine on the T-7A trainer aircraft using acoustic holography. Apparent BSN sources are identified along the nozzle lipline and corroborated with in-situ imaging. The observed shock spacing aligns with similar jets in the literature but deviates significantly from traditional analytical models. Likewise, BSN peak frequencies at forward angles match trends from other full-scale jets but differ from simulations and lab-scale data, likely due to temperature and scale-related differences. A widely used BSN frequency model underperforms when relying on historical analytic shock spacing predictions but yields excellent agreement when corrected with measured spacing. Coherence analysis reveals connections between upstream-directed BSN and downstream Mach wave radiation, and shows elevated coherence between shock cells, indicating a partially coherent, distributed BSN source.