The acoustic response of a nozzle flow to an externally applied low frequency pressure field
✍ Scribed by J.R. Jacques
- Publisher
- Elsevier Science
- Year
- 1975
- Tongue
- English
- Weight
- 1018 KB
- Volume
- 41
- Category
- Article
- ISSN
- 0022-460X
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✦ Synopsis
A theoretical discussion is presented of the noise generated when a jet exhausts from a constant pressure plenum chamber into an unsteady atmosphere. That unsteadiness provokes fluctuations at the nozzle exit and these are evaluated by taking into account a model of the axisymmetricjet instability modes. It is found that the radiated noise is virtually omnidirectional and that it depends strongly on both the jet Mach number and nozzle contraction ratio. This sound mechanism vanishes completely when the jet becomes sonic. Then, despite the unsteady external field, the nozzle flow is unperturbed. The sound power radiated scales on the sixth power of jet speed so that it is likely to dominate over the jet mixing noise at low Mach number. The mechanism can be driven by any aerodynamic perturbation around the nozzle, but it is found that if the perturbation is acoustic, the scattered energy is an altogether negligible fraction of that incident on the nozzle area.