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Study the Flow behind a Semi-Circular Step Cylinder (Laser Doppler Velocimetry (LDV) and Computational Fluid Dynamics (CFD))
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0002-4546-1607
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0002-1033-0244
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0001-9789-6293
Number of Authors: 32017 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 3, article id 332Article in journal (Refereed) Published
Abstract [en]

Laser Doppler Velocimetry (LDV) measurements, flow visualizations and unsteadyReynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) simulations havebeen carried out to study the turbulent wake that is formed behind a semi-circular step cylinder ata constant flow rate. The semi-circular cylinder has two diameters, a so-called step cylinder. Theresults from the LDV measurements indicate that wake length and vortex shedding frequency varieswith the cylinder diameter. This implies that a step cylinder can be used to attract fish of differentsize. By visualizations of the formation of a recirculation region and the well-known von Kármánvortex street behind the cylinder are disclosed. The simulation results predict the wake length andshedding frequency well for the flow behind the large cylinder but fail to capture the dynamics ofthe flow near the step in diameter to some extent and the flow behind the small cylinder to a largerextent when compared with measurements.

Place, publisher, year, edition, pages
http://www.mdpi.com/: MDPI, 2017. Vol. 10, no 3, article id 332
Keywords [en]
laser doppler velocimetry (LDV); computational fluid dynamics (CFD); fish migration; step cylinder; shedding; vortex street
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-62378DOI: 10.3390/en10030332ISI: 000398736700072Scopus ID: 2-s2.0-85017626866OAI: oai:DiVA.org:ltu-62378DiVA, id: diva2:1080371
Note

Validerad; 2017; Nivå 2; 2017-03-13 (andbra)

Available from: 2017-03-10 Created: 2017-03-10 Last updated: 2019-04-03Bibliographically approved
In thesis
1. Laser Based Flow Measurements to Evaluate Hydraulic Conditions for Migrating Fish and Benthic Fauna
Open this publication in new window or tab >>Laser Based Flow Measurements to Evaluate Hydraulic Conditions for Migrating Fish and Benthic Fauna
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Laserbaseradeflödesmätningar för utvärdering av hydrauliska förhållanden för vandrande fisk ochbottenfauna
Abstract [en]

Hydropower is one of the main sources for Sweden’s energy, which is clean and renewable. It is a clean energy source because no fuels are burned which does not pollute the air and it is a renewable energy source as it only uses natural water cycle for generating energy. However, hydropower has some consequences in nature, such as creating dams in rivers and changing water flow directions, which alters the natural behaviour of the river. These problems are mostly studied from a biological point of view but more detailed studies are required from a fundamental fluid mechanics point of view. For instance, fish migrates when an ecological imbalance is created and one of the reasons for this imbalance is having dams for hydropower that alter the natural flow of the river. This flow alteration of the river flow has other environmental effects such as flow alteration changes benthic (bottom) structure of the riverbed or stream that affects the fish and invertebrates. Fishes, as well as invertebrates, are adapted for different flows and habitats but flow alteration affects their life cycles. Therefore, flow measurements when the flow is altered due to the hydropower are one of the important issues concerning environmental problems. These flow measurements in the lab scale can increase the understanding of what happens in a river when the flow is altered.

Flow characteristic measurements can provide quantitative information on the velocity distribution in the altered flow. Recent studies suggest that turbulence created due to flow alteration has a major effect on fish migration, for example, attracting fishes to enter fishway. This is why obtaining flow information from well-defined turbulent flows, such as flow past cylindrical objects is one of the prime objectives of work. However, flow alteration due to the dam for hydropower production has a significant environmental effect on the river ecosystem. Lotic species often adapt to prevailing flow conditions; and as a crude example, two species of caddis larvae: Hydropsyche instabilis and Plectrocnemia conspersa respectively are found to thrive on fast and slow-moving water flows. For some instances, changes in river velocity may merely mean the relocation of one species whilst the flourishing of another. Therefore, flow measurement in stones embedded riverbed in lab scale is another important objective of this work.

Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) have become the most popular and promising techniques for these types of non-contact flow measurements. PIV techniques are used to visualize and measure the flow characteristic in a selected area while LDV techniques are suited for point-based measurement.  The works included in this thesis are reviewing PIV techniques previously used in fish movement related studies, LDV measurements both at upstream (bow wake) and downstream wake of vertical cylindrical obstructions, Computational Fluid Dynamics (CFD) simulations to supplement wake information and PIV measurements over the horizontal semicircular cylinders to explore wall shear stress. Apart from this, flow visualization was also included in this work. The results from all these works can be useful to evaluate hydraulic conditions for migrating fish and benthic fauna.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Fish Migration; Step Cylinder; Shedding; Vortex Street; Shear stress; PIV; benthic fauna; river; stones
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-73021 (URN)978-91-7790-318-5 (ISBN)978-91-7790-319-2 (ISBN)
Public defence
2019-04-26, E632, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2019-02-26 Created: 2019-02-26 Last updated: 2019-04-16Bibliographically approved

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