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Spectral analysis of jet turbulence

Schmidt, Oliver T. and Towne, Aaron and Rigas, Georgios and Colonius, Tim and Brès, Guillaume A. (2018) Spectral analysis of jet turbulence. Journal of Fluid Mechanics, 855 . pp. 953-982. ISSN 0022-1120. http://resolver.caltech.edu/CaltechAUTHORS:20180618-080041218

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Abstract

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.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1017/jfm.2018.675DOIArticle
https://arxiv.org/abs/1711.06296arXivDiscussion Paper
ORCID:
AuthorORCID
Schmidt, Oliver T.0000-0002-7097-0235
Towne, Aaron0000-0002-7315-5375
Rigas, Georgios0000-0001-6692-6437
Colonius, Tim0000-0003-0326-3909
Brès, Guillaume A.0000-0003-2507-8659
Additional Information:© 2018 Cambridge University Press. Received 9 November 2017; revised 7 June 2018; accepted 16 August 2018; first published online 21 September 2018. O.T.S., T.C. and G.R. gratefully acknowledge support from the US Office of Naval Research under contract N00014-16-1-2445. The LES studies were supported by NAVAIR SBIR project under the supervision of J. T. Spyropoulos, with computational resources provided by DoD HPCMP at the ERDC DSRC supercomputer facility.
Funders:
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-16-1-2445
Naval Air Systems Command (NAVAIR)UNSPECIFIED
Subject Keywords:absolute/convective instability, jet noise, shear layer turbulence
Record Number:CaltechAUTHORS:20180618-080041218
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180618-080041218
Official Citation:Schmidt, O., Towne, A., Rigas, G., Colonius, T., & Brès, G. (2018). Spectral analysis of jet turbulence. Journal of Fluid Mechanics, 855, 953-982. doi:10.1017/jfm.2018.675
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87180
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:18 Jun 2018 21:15
Last Modified:08 Oct 2018 21:42

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