Spectral analysis of jet turbulence

Informed by large-eddy simulation (LES) data and resolvent analysis of the mean flow, we examine the structure of turbulence in jets in the subsonic, transonic and supersonic regimes. Spectral (frequency-space) proper orthogonal decomposition is used to extract energy spectra and decompose the flow...

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Vydáno v:Journal of fluid mechanics Ročník 855; s. 953 - 982
Hlavní autoři: Schmidt, Oliver T., Towne, Aaron, Rigas, Georgios, Colonius, Tim, Brès, Guillaume A.
Médium: Journal Article
Jazyk:angličtina
Vydáno: Cambridge, UK Cambridge University Press 25.11.2018
Témata:
Acoustics
Analysis
Data processing
Eddy kinetic energy
Energy spectra
Experiments
Fluid dynamics
JFM Papers
Large eddy simulation
Modes
Noise
Nozzle geometry
Nozzles
Numerical analysis
Oceanic eddies
Predictions
Proper Orthogonal Decomposition
Reynolds number
Shear
Spectral analysis
Stability
Stability analysis
Turbulence
United States > US
shear layer turbulence
absolute/convective instability
jet noise
ISSN:0022-1120, 1469-7645
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Popis
Shrnutí:Informed by large-eddy simulation (LES) data and resolvent analysis of the mean flow, we examine the structure of turbulence in jets in the subsonic, transonic and supersonic regimes. Spectral (frequency-space) proper orthogonal decomposition is used to extract energy spectra and decompose the flow into energy-ranked coherent structures. The educed structures are generally well predicted by the resolvent analysis. Over a range of low frequencies and the first few azimuthal mode numbers, these jets exhibit a low-rank response characterized by Kelvin–Helmholtz (KH) type wavepackets associated with the annular shear layer up to the end of the potential core and that are excited by forcing in the very-near-nozzle shear layer. These modes too have been experimentally observed before and predicted by quasi-parallel stability theory and other approximations – they comprise a considerable portion of the total turbulent energy. At still lower frequencies, particularly for the axisymmetric mode, and again at high frequencies for all azimuthal wavenumbers, the response is not low-rank, but consists of a family of similarly amplified modes. These modes, which are primarily active downstream of the potential core, are associated with the Orr mechanism. They occur also as subdominant modes in the range of frequencies dominated by the KH response. Our global analysis helps tie together previous observations based on local spatial stability theory, and explains why quasi-parallel predictions were successful at some frequencies and azimuthal wavenumbers, but failed at others.
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ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2018.675