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- Title
Source-mechanism identification by nearfield-farfield pressure correlations in subsonic jets.
- Authors
Laurendeau, E.; Jordan, P.; Delville, J.; Bonnet, J.-P.
- Abstract
Simultaneous pressure measurements are performed in the near and farfield regions of a subsonic jet, and natural and fluidically controlled cases are studied. The measurements are used to examine: (1) the causal relationship between the coherent dynamic of the flow and the sound field it produces; and, (2) the localisation and directive character of a broadband high-frequency component of the sound field which is sometimes associated with the fine-scale turbulence. By varying the axial and radial positions of a nearfield microphone, correlations with 10 farfield microphones are used to study the source signatures in three regions: the near-nozzle region (nearfield microphone at x/D = 1), the mixing-layer region (nearfield microphone at x/D = 3), and the end of the potential core (nearfield microphone at x/D = 5). The correlations reveal a number of distinctive signatures in both baseline and controlled flows, and arguments are presented which relate these to the following kinds of source mechanism: (1) a wavy-wall mechanism associated with Kelvin-Helmholtz structures in the initial stages of the flow, and which comprises a distinctive tri-modal structure with marked directivity patterns in the upstream regions; (2) a more monochromatic wave-like mechanism at the end of the potential core; (3) a broadband high-frequency source whose directivity is a strong function of axial position, in contrast with the common assumption that this component radiates omnidirectionally; and, (4) a highly directive, localised source associated with vortex shedding from the blunt trailing edge of the nozzle. The comparison of results between the controlled and uncontrolled cases demonstrates the relative inefficiency of this kind of control in producing a fundamental change in the said source mechanisms.
- Subjects
AERODYNAMICS; BOUNDARY layer noise; MICROPHONES; TURBULENCE; NOISE
- Publication
International Journal of Aeroacoustics, 2008, Vol 7, Issue 1, p41
- ISSN
1475-472X
- Publication type
Article
- DOI
10.1260/147547208784079908