Linearised dynamics and non-modal instability analysis of an impinging under-expanded supersonic jet

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Title: Linearised dynamics and non-modal instability analysis of an impinging under-expanded supersonic jet
Authors: Karami, S
Stegeman, PC
Theofilis, V
Schmid, PJ
Soria, J
Item Type: Conference Paper
Abstract: Non-modal instability analysis of the shear layer near the nozzle of a supersonic under-expanded impinging jet is studied. The shear layer instability is considered to be one of the main components of the feedback loop in supersonic jets. The feedback loop is observed in instantaneous visualisations of the density field where it is noted that acoustic waves scattered by the nozzle lip internalise as shear layer instabilities. A modal analysis describes the asymptotic limit of the instability disturbances and fails to capture short-time responses. Therefore, a non-modal analysis which allows the quantitative description of the short-time amplification or decay of a disturbance is performed by means of a local far-field pressure pulse. An impulse response analysis is performed which allows a wide range of frequencies to be excited. The temporal and spatial growths of the disturbances in the shear layer near the nozzle are studied by decomposing the response using dynamic mode decomposition and Hilbert transform analysis. The short-time response shows that disturbances with non-dimensionalised temporal frequencies in the range of 1 to 4 have positive growth rates in the shear layer. The Hilbert transform analysis shows that high non-dimensionalised temporal frequencies (>4) are dampened immediately, whereas low non-dimensionalised temporal frequencies (<1) are neutral. Both dynamic mode decomposition and Hilbert transform analysis show that spatial frequencies between 1 and 3 have positive spatial growth rates. Finally, the envelope of the streamwise velocity disturbances reveals the presence of a convective instability.
Editors: Jimenez, J
Issue Date: 1-Jan-2018
Date of Acceptance: 29-May-2017
ISSN: 1742-6588
Publisher: Institute of Physics (IoP)
Journal / Book Title: Journal of Physics : Conference Series
Volume: 1001
Issue: Conference 1
Copyright Statement: © 2018 IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence ( Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Conference Name: Third Madrid Summer School on Turbulence
Keywords: Science & Technology
Physical Sciences
Physics, Applied
Physics, Multidisciplinary
02 Physical Sciences
09 Engineering
Publication Status: Published
Start Date: 2017-05-29
Finish Date: 2017-06-30
Conference Place: Univ Politecnica Madrid, Sch Aeronaut, Madrid, Spain
Online Publication Date: 2018-04-12
Appears in Collections:Applied Mathematics and Mathematical Physics
Faculty of Natural Sciences

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