Upstream-travelling acoustic jet modes as a closure mechanism for screech

Experimental evidence is provided to demonstrate that the upstream-travelling waves in two jets screeching in the A1 and A2 modes are not free-stream acoustic waves, but rather waves with support within the jet. Proper orthogonal decomposition is used to educe the coherent fluctuations associated wi...

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Bibliographic Details
Published in:Journal of fluid mechanics 2018-11, Vol.855, Article R1
Main Authors: Edgington-Mitchell, Daniel, Jaunet, Vincent, Jordan, Peter, Towne, Aaron, Soria, Julio, Honnery, Damon
Format: Article
Language:English
Subjects:
Acoustics
Computational fluid dynamics
Engineering Sciences
Fluids mechanics
Fourier transforms
Frequency ranges
JFM Rapids
Mechanics
Noise
Nozzle geometry
Phase velocity
Propagation
Proper Orthogonal Decomposition
Reactive fluid environment
Screech tones
Sheet modelling
Sound waves
Traveling waves
Upstream
Variation
Velocity distribution
Vortices
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Summary:Experimental evidence is provided to demonstrate that the upstream-travelling waves in two jets screeching in the A1 and A2 modes are not free-stream acoustic waves, but rather waves with support within the jet. Proper orthogonal decomposition is used to educe the coherent fluctuations associated with jet screech from a set of randomly sampled velocity fields. A streamwise Fourier transform is then used to isolate components with positive and negative phase speeds. The component with negative phase speed is shown, by comparison with a vortex-sheet model, to resemble the upstream-travelling jet wave first studied by Tam & Hu (J. Fluid Mech., vol. 201, 1989, pp. 447–483). It is further demonstrated that screech tones are only observed over the frequency range where this upstream-travelling wave is propagative.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2018.642