Session 1pNS: Noise 1pNS5. On near-field acoustical inverse measurements of partially coherent sources

The sources of jet noise have been investigated through the use of near-field array measurements. An understanding of spatial coherence properties in the jet near field leads to insight about source composition. A metric called coherence length is a useful tool for summarizing near-field coherence information. Near-field coherence lengths are presented in this work for a full-scale jet, which show that jet noise is composed of two distinct components: (1) highly spatially coherent, low-frequency, large-scale turbulent structures and (2) high-frequency fine-scale turbulence with very low spatial coherence. The spatial extent and coherence of jet noise sources support the use of near-field acoustical holography as a viable jet-noise-source imaging technique.