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On the scaling and topology of confined bluff-body flows
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).ORCID iD: 0000-0003-0976-2004
2019 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 876, p. 1018-1040Article in journal (Refereed) Published
Abstract [en]

An experimental study of bluff bodies in confinement is presented. Two Reynolds matched rigs (pipe diameters: D D 40 mm and D D 194 mm) are used to derive a picture of the flow topology of the primary-shedding mode (Karman vortex, mode-I). Confined bluff bodies create an additional spectral mode (mode-II). This is caused by the close coupling of the shedder blockage and the wall and is unique to the confined bluff-body problem. Under certain conditions, modes-I and II can interact, resulting in a lock-on, wherein the modes cease to exist at independent frequencies. The topological effects of mode interaction are demonstrated using flow visualisation. Furthermore, the scaling of mode-II is explored. The two experimental facilities span Reynolds numbers (based on the shedder diameter, d) 104 < Red < 105 and bulk Mach numbers 0 : 02 < Mb < 0 : 4. Bluff bodies with a constant blockage ratio (d = D), forebody shape and various splitter-plate lengths (l) and thicknesses (t) are used. Results indicate that the flow topology changes substantially between short (l < d) and long (l > d) tailed geometries. Surface flow visualisation indicates that the primary vortex becomes anchored on the tail when l & 3h (2h D d t). This criterion prohibits the development of such a topology for short-tailed geometries. When mode interaction occurs, which it does exclusively in long-tailed cases, the tail-anchored vortex pattern is disrupted. The onset of mode-II occurs at approximately the same Reynolds number in both rigs, although the associated dimensionless frequency is principally a function of Mach number. Accordingly, mode interaction is avoided in the larger-scale rig, due to the increased separation of the modal frequencies.

Place, publisher, year, edition, pages
Cambridge University Press, 2019. Vol. 876, p. 1018-1040
Keywords [en]
vortex shedding, vortex streets
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Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-257425DOI: 10.1017/jfm.2019.583ISI: 000480580100001Scopus ID: 2-s2.0-85070742692OAI: oai:DiVA.org:kth-257425DiVA, id: diva2:1347772
Note

QC 20190902

Available from: 2019-09-02 Created: 2019-09-02 Last updated: 2019-10-04Bibliographically approved

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Ford, Christopher L.

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