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Characterization of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. (Strömningslära)ORCID iD: 0000-0001-9426-2375
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. (Strömningslära)ORCID iD: 0000-0002-4916-9566
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0002-8360-9051
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall Research and Development, Älvkarleby.
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2018 (English)In: Engineering, ISSN 1947-3931, Vol. 10, p. 399-416Article in journal (Refereed) Published
Abstract [en]

High Reynolds number flow inside a channel of rectangular cross section is examined using Particle Image Velocimetry. One wall of the channel has been replaced with a surface of a roughness representative to that of real hydropower tunnels, i.e. a random terrain with roughness dimensions typically in the range of ≈10% - 20% of the channels hydraulic radius. The rest of the channel walls can be considered smooth. The rough surface was captured from an existing blasted rock tunnel using high resolution laser scanning and scaled to 1:10. For quantification of the size of the largest flow structures, integral length scales are derived from the auto-correlation functions of the temporally averaged velocity. Additionally, Proper Orthogonal Decomposition (POD) and higher-order statistics are applied to the instantaneous snapshots of the velocity fluctuations. The results show a high spatial heterogeneity of the velocity and other flow characteristics in vicinity of the rough surface, putting outer similarity treatment into jeopardy. Roughness effects are not confined to the vicinity of the rough surface but can be seen in the outer flow throughout the channel, indicating a different behavior than postulated by Townsend’s similarity hypothesis. The effects on the flow structures vary depending on the shape and size of the roughness elements leading to a high spatial dependence of the flow above the rough surface. Hence, any spatial averaging, e.g. assuming a characteristic sand grain roughness factor, for determining local flow parameters becomes less applicable in this case.

Place, publisher, year, edition, pages
Scientific Research Publishing, 2018. Vol. 10, p. 399-416
Keywords [en]
CFD, Validation, Hydraulic Roughness, PIV, Hydropower
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-71097DOI: 10.4236/eng.2018.107028OAI: oai:DiVA.org:ltu-71097DiVA, id: diva2:1253280
Available from: 2018-10-04 Created: 2018-10-04 Last updated: 2019-08-12Bibliographically approved
In thesis
1. Modelling flow over rough surfaces in hydropower waterways
Open this publication in new window or tab >>Modelling flow over rough surfaces in hydropower waterways
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-71104 (URN)978-91-7790-224-9 (ISBN)978-91-7790-225-6 (ISBN)
Public defence
2018-11-23, E632, Luleå tekniska universitet, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2018-10-08 Created: 2018-10-04 Last updated: 2018-11-21Bibliographically approved

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Andersson, L. RobinLarsson, SofiaHellström, J. Gunnar I.Andreasson, PatrikAndersson, Anders G.Lundström, Staffan

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