On the impact of swirl on the growth of coherent structures

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dc.contributor.authorOberleithner, Kilian
dc.contributor.authorPaschereit, Christian Oliver
dc.contributor.authorWygnanski, I.
dc.date.accessioned2017-10-27T12:54:47Z
dc.date.available2017-10-27T12:54:47Z
dc.date.issued2014
dc.descriptionDieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.de
dc.descriptionThis publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.en
dc.description.abstractSpatial linear stability analysis is applied to the mean flow of a turbulent swirling jet at swirl intensities below the onset of vortex breakdown. The aim of this work is to predict the dominant coherent flow structure, their driving instabilities and how they are affected by swirl. At the nozzle exit, the swirling jet promotes shear instabilities and, less unstable, centrifugal instabilities. The latter stabilize shortly downstream of the nozzle, contributing very little to the formation of coherent structures. The shear mode remains unstable throughout generating coherent structures that scale with the axial shear-layer thickness. The most amplified mode in the nearfield is a co-winding double-helical mode rotating slowly in counter-direction to the swirl. This gives rise to the formation of slowly rotating and stationary large-scale coherent structures, which explains the asymmetries in the mean flows often encountered in swirling jet experiments. The co-winding single-helical mode at high rotation rate dominates the farfield of the swirling jet in replacement of the co- and counter-winding bending modes dominating the non-swirling jet. Moreover, swirl is found to significantly affect the streamwise phase velocity of the helical modes rendering this flow as highly dispersive and insensitive to intermodal interactions, which explains the absence of vortex pairing observed in previous investigations. The stability analysis is validated through hot-wire measurements of the flow excited at a single helical mode and of the flow perturbed by a time- and space-discrete pulse. The experimental results confirm the predicted mode selection and corresponding streamwise growth rates and phase velocities.en
dc.identifier.eissn1469-7645
dc.identifier.issn0022-1120
dc.identifier.urihttps://depositonce.tu-berlin.de/handle/11303/7065
dc.identifier.urihttp://dx.doi.org/10.14279/depositonce-6374
dc.language.isoen
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/
dc.subject.ddc530 Physik
dc.subject.otherabsolute/convective instabilityen
dc.subject.otherturbulent flowsen
dc.subject.otherwakes/jetsen
dc.titleOn the impact of swirl on the growth of coherent structuresen
dc.typeArticle
dc.type.versionpublishedVersion
dcterms.bibliographicCitation.doi10.1017/jfm.2013.669
dcterms.bibliographicCitation.journaltitleJournal of fluid mechanics
dcterms.bibliographicCitation.originalpublishernameCambridge University Press
dcterms.bibliographicCitation.originalpublisherplaceCambridge
dcterms.bibliographicCitation.pageend199
dcterms.bibliographicCitation.pagestart156
dcterms.bibliographicCitation.volume741
tub.accessrights.dnbdomain
tub.affiliationFak. 5 Verkehrs- und Maschinensysteme::Inst. Strömungsmechanik und Technische Akustik (ISTA)::FG Experimentelle Strömungsmechanikde
tub.affiliation.facultyFak. 5 Verkehrs- und Maschinensystemede
tub.affiliation.groupFG Experimentelle Strömungsmechanikde
tub.affiliation.instituteInst. Strömungsmechanik und Technische Akustik (ISTA)de
tub.publisher.universityorinstitutionTechnische Universität Berlin

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