A numerical study of the laminar necklace vortex system and its effect on the wake for a circular cylinder

dc.contributor.authorKirkil, Gökhan
dc.contributor.authorConstantinescu, George
dc.date.accessioned2019-06-27T08:04:03Z
dc.date.available2019-06-27T08:04:03Z
dc.date.issued2012
dc.departmentFakülteler, Mühendislik ve Doğa Bilimleri Fakültesi, Endüstri Mühendisliği Bölümüen_US
dc.description.abstractLarge eddy simulation (LES) is used to investigate the structure of the laminar horseshoe vortex (HV) system and the dynamics of the necklace vortices as they fold around the base of a circular cylinder mounted on the flat bed of an open channel for Reynolds numbers defined with the cylinder diameter D smaller than 4460. The study concentrates on the analysis of the structure of the HV system in the periodic breakaway sub-regime which is characterized by the formation of three main necklace vortices. Over one oscillation cycle of the previously observed breakaway sub-regime the corner vortex and the primary vortex merge (amalgamate) and a developing vortex separates from the incoming laminar boundary layer (BL) to become the new primary vortex. Results show that while the classical breakaway sub-regime in which one amalgamation event occurs per oscillation cycle is present when the nondimensional displacement thickness of the incoming BL at the location of the cylinder is relatively large (delta*/D > 0.1) a new type of breakaway sub-regime is present for low values of delta*/D. This sub-regime which we call the double-breakaway sub-regime is characterized by the occurrence of two amalgamation events over one full oscillation cycle. LES results show that when the HV system is in one of the breakaway sub-regimes the interactions between the highly coherent necklace vortices and the eddies shed inside the separated shear layers (SSLs) are very strong. For the relatively shallow flow conditions considered in this study (H/D congruent to 1 H is the channel depth) at times the disturbances induced by the legs of the necklace vortices do not allow the SSLs on the two sides of the cylinder to interact in a way that allows the vorticity redistribution mechanism to lead to the formation of a new wake roller. As a result the shedding of large-scale rollers in the turbulent wake is suppressed for relatively large periods of time. Simulation results show that the wake structure changes randomly between time intervals when large-scale rollers are forming and are convected in the wake (von Karman regime) and time intervals when the rollers do not form. When the wake is in the von Karman regime the shedding frequency of the rollers is close to that observed for flow past infinitely long cylinders.en_US]
dc.identifier.citation41
dc.identifier.doi10.1063/1.4731291en_US
dc.identifier.issn1070-6631en_US
dc.identifier.issn1089-7666en_US
dc.identifier.issn1070-6631
dc.identifier.issn1089-7666
dc.identifier.issue7
dc.identifier.scopus2-s2.0-84864772382en_US
dc.identifier.scopusqualityQ1
dc.identifier.urihttps://hdl.handle.net/20.500.12469/883
dc.identifier.urihttps://doi.org/10.1063/1.4731291
dc.identifier.volume24en_US
dc.identifier.wosWOS:000308406000018en_US
dc.identifier.wosqualityQ1
dc.institutionauthorKirkil, Gökhanen_US
dc.language.isoenen_US
dc.publisherAmer Inst Physicsen_US
dc.relation.journalPhysics of Fluidsen_US
dc.relation.publicationcategoryMakale - Uluslararası Hakemli Dergi - Kurum Öğretim Elemanıen_US
dc.rightsinfo:eu-repo/semantics/openAccessen_US
dc.subjectBoundary layersen_US
dc.subjectConvectionen_US
dc.subjectExternal flowsen_US
dc.subjectFlow separationen_US
dc.subjectFlow simulationen_US
dc.subjectFluid oscillationsen_US
dc.subjectLaminar flowen_US
dc.subjectNumerical analysisen_US
dc.subjectTurbulenceen_US
dc.subjectVorticesen_US
dc.subjectWakesen_US
dc.titleA numerical study of the laminar necklace vortex system and its effect on the wake for a circular cylinderen_US
dc.typeArticleen_US
dspace.entity.typePublication
relation.isAuthorOfPublicationc777ed76-9b8f-43f2-a3b0-0222883181af
relation.isAuthorOfPublication.latestForDiscoveryc777ed76-9b8f-43f2-a3b0-0222883181af

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