| 1. |
- Andersson, L. Robin, et al.
(författare)
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Localized roughness effects in non-uniform hydraulic waterways
- 2021
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Ingår i: Journal of Hydraulic Research. - : Taylor & Francis. - 0022-1686 .- 1814-2079. ; 59:1, s. 100-108
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Tidskriftsartikel (refereegranskat)abstract
- Hydropower tunnels are generally subject to a degree of rock falls. Studies explaining this are scarce and the current industrial standards offer little insight. To simulate tunnel conditions, high Reynolds number flow inside a channel with a rectangular cross-section is investigated using Particle Image Velocimetry and pressure measurements. For validation, the flow is modelled using LES and a RANS approach with k - ε turbulence model. One wall of the channel has been replaced with a rough surface captured using laser scanning. The results indicate flow-roughness effects deviating from the standard non-asymmetric channel flow and hence, can not be properly predicted using spatially averaged relations. These effects manifest as localized bursts of velocity connected to individual roughness elements. The bursts are large enough to affect both temporally and spatially averaged quantities. Both turbulence models show satisfactory agreement for the overall flow behaviour, where LES also provided information for in-depth analysis.
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| 2. |
- Andersson, L. Robin, et al.
(författare)
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Characterization of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations
- 2018
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Ingår i: Engineering. - : Scientific Research Publishing. - 1947-3931 .- 1947-394X. ; 10, s. 399-416
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Andersson, L. Robin, 1987-, et al.
(författare)
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Estimating localized pressure fluctuations in Gävunda hydropower tunnel
- 2020
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Ingår i: Proceedings of the 8th IAHR International Symposium on Hydraulic Structures ISHS2020. - : The University of Queensland.
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Konferensbidrag (refereegranskat)abstract
- A numerical investigation of a hydropower tunnel has been implemented in this project. The tunnel geometry data were taken from a laser scanning of a tunnel positioned in Gävunda, Sweden. While the average cross-section of the tunnel is even, in accordance with the pre-excavation schematics, the instantaneous deviations are significant. ANSYS-CFX was applied for the simulations using a RANS approach with k-ε model for turbulence closure. To evaluate the results, the pressure was area averaged in 30 planes evenly spaced perpendicular to the flow direction inside the tunnel. Additionally, the pressure was sampled along a line running from the inlet to the outlet of the tunnel. Results show that the area averaged pressure is similar to the pressure modelled along the center line. This means that the roughness has a dominating effect on the bulk flow inside of the tunnel. Hence, cross-sectional based methods of evaluation (e.g. Gauckler-Manning) could potentially be used to evaluate the localized pressure inside the tunnel. Further evaluation show that the Gauckler-Manning and Haaland equation both can be used as an estimate of the modelled pressure inside of the tunnel. Both equations are highly dependent on the hydraulic radius and cross-sectional area. These results have many implications, continuous pressure measurements can potentially be used to monitor the structural integrity of tunnels. Similarly, tunnel data could be used to estimate pressure effects within the tunnel, which would enable easier and reliable risk assessment studies.
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| 4. |
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| 5. |
- Andersson, Robin, 1987-, et al.
(författare)
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Gävunda case study
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Andersson, Robin, et al.
(författare)
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Inlet Blockage Effects in a Free Surface Channel With Artificially Generated Rough Walls
- 2018
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Ingår i: Proceedings of the 7th IAHR International Symposium on Hydraulic Structures. - 9780692132777 ; , s. 723-732
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Konferensbidrag (refereegranskat)abstract
- When considering free surface flow in channels, it is essential to have in-depth knowledge about the inlet flow conditions and the effect of surface roughness on the overall flow field. Hence, we hereby investigate flow inside an 18m long channel by using Particle Tracking Velocimetry (PTV) and Acoustic Doppler Velocimetry (ADV). The roughness of the channel walls is generated using a diamond-square fractal algorithm and is designed to resemble the actual geometry of hydropower tunnels. Four different water levels ranging from 20 to 50cm are investigated. For each depth, the inlet is blocked by 25 and 50% at three positions each, at the centre, to the right and to the left in the flow-direction. The flow is altered for each depth to keep the flow velocity even throughout the measurements. PTV is applied to measure the velocity of the free water surface; four cameras are placed above the setup to capture the entirety of the channel. The results show a clear correlation between roughness-height and velocity distribution at depths 20-30 cm. The surface roughness proved effective in dispersing the subsequent perturbations following the inlet blockage. At 50cm, perturbations from the 50% blockage could be observed throughout the channel. However, at 20cm, most perturbations had subsided by a third of the channel length. The ADV was used to capture the velocity in a total of 375 points throughout the channel, at a depth of 50 cm with no inlet perturbations.
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| 7. |
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| 8. |
- Andersson, Robin, 1987-, et al.
(författare)
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Numerical investigation of a hydropower tunnel : Estimating localised head-loss using the manning equation
- 2019
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Ingår i: Water. - : MDPI. - 2073-4441. ; 11:8
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Tidskriftsartikel (refereegranskat)abstract
- The fluid dynamics within a water tunnel is investigated numerically using a RANS approach with the k-ε turbulence model. The computational model is based on a laser scan of a hydropower tunnel located in Gävunda, Sweden. The tunnel has a typical height of 6.9 m and a width of 7.2 m. While the average cross-sectional shape of the tunnel is smooth the local deviations are significant, where some roughness elements may be in the size of 5 m implying a large variation of the hydraulic radius. The results indicate that the Manning equation can successfully be used to study the localised pressure variations by taking into account the varying hydraulic radius and cross-sectional area of the tunnel. This indicates a dominant effect of the tunnel roughness in connection with the flow, which has the potential to be used in the future evaluation of tunnel durability. ANSYS-CFX was used for the simulations along with ICEM-CFD for building the mesh.
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| 9. |
- Hedberg, P. A. Mikael, et al.
(författare)
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Measurements and Simulations of the Flow Distribution in a Down-Scaled Multiple Outlet Spillway with Complex Channel
- 2024
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Ingår i: Water. - : Multidisciplinary Digital Publishing Institute (MDPI). - 2073-4441. ; 16:6
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of mass flow through a three-outlet spillway modeled after a scaled-down spillway were conducted. The inlet and channel leading up to the outlets were placed to lead the water toward the outlet at an angle. With this, measurements of the water level at three locations were recorded by magnetostrictive sensors. The volumetric flow rates for each individual outlet were recorded separately to study the differences between them. Additionally, Acoustic Doppler Velocimetry was used to measure water velocities close to the outlets. The conditions changed were the inlet volume flow rate and the flow distribution was measured at 90, 100, 110, and 200 L per second. Differences between the outlets were mostly within the error margin of the instruments used in the experiments with larger differences shown for the 200 L test. The results produced together with a CAD model of the setup can be used for verification of CFD methods. A simulation with the k-epsilon turbulence model is included and compared to earlier experiments and the new experimental results. Larger differences are seen in the new experiments. Differing inlet conditions are assumed as the principal cause for the differences seen.
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| 10. |
- Hedberg, P. A. Mikael, 1989-, et al.
(författare)
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Numerical modelling of flow in parallel spillways
- 2020
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Ingår i: Proceedings of the 8th IAHR International Symposium on Hydraulic Structures ISHS2020. - : The University of Queensland.
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Konferensbidrag (refereegranskat)abstract
- Mathematical modelling of single spillways is well documented in literature. For parallel spillways however, there is a lack of documented, verified, and validated cases. Here, in this article, ANSYS-CFX is used to simulate the flow over three parallel ogee-crested spillways. For mesh size verification, a grid convergence study is performed by Richardson extrapolation. The turbulence model chosen for this simulation is the k-ε model and the volume of fluid method is used to simulate the water-air interface. This article details the models ability to accurately predict flow distribution at the spillways, and the water levels. The mesh is kept relatively coarse at the channel inlet with increased mesh density at the spillways. The results are validated against experimental data from Vattenfall AB, R&Ds laboratories. The geometry and boundary conditions of the experiment are tailored for CFD. The flow rate of each spillway is measured separately with high accuracy, and for several different inlet volumetric flows. The simulation results lie within the error estimates of the measuring tools used in the experiments, within ±1%. The volume flow rate differences between the three outlets is very small, within ±1%.
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