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Flow topology of rare back flow events and critical points in turbulent channels and toroidal pipes
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-6570-5499
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-1663-3553
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2018 (English)In: Journal of Physics: Conference Series, Institute of Physics Publishing (IOPP), 2018, Vol. 1001, no 1, article id 012002Conference paper, Published paper (Refereed)
Abstract [en]

A study of the back flow events and critical points in the flow through a toroidal pipe at friction Reynolds number Reτ ≈ 650 is performed and compared with the results in a turbulent channel flow at Reτ ≈ 934. The statistics and topological properties of the back flow events are analysed and discussed. Conditionally-averaged flow fields in the vicinity of the back flow event are obtained, and the results for the torus show a similar streamwise wall-shear stress topology which varies considerably for the spanwise wall-shear stress when compared to the channel flow. The comparison between the toroidal pipe and channel flows also shows fewer back flow events and critical points in the torus. This cannot be solely attributed to differences in Reynolds number, but is a clear effect of the secondary flow present in the toroidal pipe. A possible mechanism is the effect of the secondary flow present in the torus, which convects momentum from the inner to the outer bend through the core of the pipe, and back from the outer to the inner bend through the pipe walls. In the region around the critical points, the skin-friction streamlines and vorticity lines exhibit similar flow characteristics with a node and saddle pair for both flows. These results indicate that back flow events and critical points are genuine features of wall-bounded turbulence, and are not artifacts of specific boundary or inflow conditions in simulations and/or measurement uncertainties in experiments.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018. Vol. 1001, no 1, article id 012002
Series
Journal of Physics: Conference Series, ISSN 1742-6588 ; 1001
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-238246DOI: 10.1088/1742-6596/1001/1/012002ISI: 000454926900002Scopus ID: 2-s2.0-85046100946OAI: oai:DiVA.org:kth-238246DiVA, id: diva2:1260117
Conference
3rd Madrid Summer School on Turbulence, School of Aeronautics of the Universidad Politecnica de MadridMadrid, Spain, 29 May 2017 through 30 June 2017
Note

QC 20181101

Available from: 2018-11-01 Created: 2018-11-01 Last updated: 2019-01-18Bibliographically approved

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Vinuesa, RicardoÖrlü, RamisNoorani, AzadSchlatter, Philipp

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