| 1. |
- Bin Asad, S M Sayeed, 1985-, et al.
(författare)
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Experimental study of the flow past submerged half-cylinders
- 2017
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Ingår i: AIP Conference Proceedings. - : American Institute of Physics (AIP). - 0094-243X .- 1551-7616. ; 1851
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Bin Asad, S M Sayeed, 1985-
(författare)
-
Laser Based Flow Measurements to Evaluate Hydraulic Conditions for Migrating Fish and Benthic Fauna
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 3. |
- Bin Asad, S M Sayeed, 1985-, et al.
(författare)
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Study the Flow behind a Semi-Circular Step Cylinder (Laser Doppler Velocimetry (LDV) and Computational Fluid Dynamics (CFD))
- 2017
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Ingår i: Energies. - Basel, Switzerland : MDPI. - 1996-1073. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Bin Asad, S M Sayeed, 1985-, et al.
(författare)
-
Velocity distribution measurements in a fishway like open channel by Laser Doppler Anemometry (LDA)
- 2016
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Konferensbidrag (refereegranskat)abstract
- Experiments in an open channel flume with placing a vertical half cylinder barrier have been performed in order to investigate how the upstream velocity profiles are affected by a barrier. An experimental technique using Laser Doppler Velocimetry (LDV) was adopted to measure these velocity distributions in the channel for four different discharge rates. Velocity profiles were measured very close to wall and at 25, 50 and 100 mm upstream of the cylinder wall. For comparing these profiles with well-known logarithmic velocity profiles, velocity profiles were also measured in smooth open channel flow for all same four discharge rates. The results indicate that regaining the logarithmic velocity profiles upstream of the half cylindrical barrier occurs at 100 mm upstream of the cylinder wall.
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| 5. |
- Bin Asad, S M Sayeed, 1985-, et al.
(författare)
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Wall shear stress measurement on curve objects with PIV in connection to benthic fauna in regulated rivers
- 2019
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Ingår i: Water. - : MDPI. - 2073-4441. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- The flow characteristics in the vicinity of a set of half-cylinders of different sizes simulating benthic objects were studied experimentally using particle image velocimetry (PIV). The cylinders were mounted on the bottom of an open channel, and the influence of the flow speed on the distribution of the shear stress along the bottom geometry was investigated. Of special interest was how the shear stress changes close to the wall as a function of the flow speed and cylinder arrangement. It was found that the shear stress varies significantly as a function of position. This implies habitat heterogeneity allowing benthic invertebrates with different shear stress tolerance exists when the bottom consists of differently sized stones. It was also shown that direct measurements of near wall velocity gradients are necessary to accurately calculate the wall shear stress for more complex geometries.
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