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Experimental study of the flow past submerged half-cylinders
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.
2017 (English)In: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 1851, article id 020001Article in journal (Refereed) Published
Abstract [en]

This investigation studies the details of the flow behind and over two identical semicircular cylinderspositioned in tandem. Laser Doppler Velocimetry (LDV) measurements are carried out in a laboratory waterflume using two different gap ratios (Sp/d = 1 and Sp/d = 0.5; where Sp indicates distance between the cylindersand d indicates cylinder diameter) under two different flow situations. These LDV measurement are used toderive velocities, formation length and Power spectral density for the various flow conditions. Flowvisualizations are also added in this investigation. The results indicate that the flow is significantly affected dueto gap ratios.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017. Vol. 1851, article id 020001
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-64318DOI: 10.1063/1.4984630ISI: 000412828600001Scopus ID: 2-s2.0-85022041470OAI: oai:DiVA.org:ltu-64318DiVA, id: diva2:1113198
Conference
7th BSME International Conference on Thermal Engineering, Dhaka, Bangladesh, 22–24 December, 2016
Note

2017-06-21 (andbra);Konferensartikel i tidskrift

Available from: 2017-06-21 Created: 2017-06-21 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: 2019-09-11Bibliographically approved

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Bin Asad, S M SayeedLundström, StaffanAndersson, Anders G.

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