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  • 1.
    Andersson, Anders G.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Modelling and validation of flow over a wall with large surface roughness2012Conference paper (Refereed)
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    FULLTEXT01
  • 2.
    Andersson, Anders G.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Effect of spatial resolution of rough surfaces on numerically computed flow fields with application to hydraulic engineering2014In: Engineering Applications of Computational Fluid Mechanics, ISSN 1994-2060, E-ISSN 1997-003X, Vol. 8, no 3, p. 373-381Article in journal (Refereed)
    Abstract [en]

    In numerical simulations of flow over rough surfaces, the roughness is often not resolved but represented by a numerical model. The validity of such an assumption is investigated in this paper by Reynolds-Averaged Navier-Stokes simulations of flow over a surface with a large roughness. The surface was created from a high-resolution laser scanning of a real rock blasted tunnel. By reducing the geometrical resolution of the roughness in two steps, the importance of an appropriate surface description could be examined. The flow fields obtained were compared to a set-up with a geometrical flat surface where the roughness was represented by a modified form of the Launder and Spalding wall-function. The flow field over the surface with the lowest resolution was substantially different from those of the two finer resolutions and rather close to the results from the set-up with the wall-function. The results also yield that the finer the resolution is the more vorticity is formed close to the rough surface and more turbulence is generated.

  • 3.
    Andersson, Anders
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Leonardsson, Kjell
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Lindberg, Dan-Erik
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundqvist, Hans
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Describing fish passage in a river confluence with telemetry and CFD2016In: / [ed] Webb, JA, Costelloe, JF, CasasMulet, R, Lyon, JP, Stewardson, MJ, Melbourne: University of Melbourne , 2016Conference paper (Refereed)
    Abstract [en]

    The confluence between hydropower tailrace and the old river bed in Stornorrfors in the river Umeälven in the northern part of Sweden has shown to be the largest obstacle for upstream migrating salmon and sea trout during the migrating season. Fish are attracted to the high flow rate from the tailrace and will not migrate upstream in the old river bed being the passage to the fishway leading past the hydropower dam. By triangulating the movements of radio tagged fish using eight antennas in the confluence, it is here possible to describe the individual fish tracks left by radio tagged fish during the migrating season. These tracks are then compared with three-dimensional Computational Fluid Dynamics (CFD) simulations of the confluence. By simulating the most common combinations of turbine flow and spill flow in the old river bed it is then possible to find correlations between individual fish movements and flow parameters such as velocity, turbulence intensity or vorticity for different flow combinations. It was previously assumed that fish had trouble locating the old river bed, the results of the triangulation however shows that most fish finds the old river bed within a few days but does not chose to migrate until several days (or weeks) later. The main issue to be solved is therefore not how to attract the fish to the old river bed but rather how to create favorable conditions in the old river bed so that migrating fish are more inclined to take that path upstream.

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  • 4.
    Andersson, L. Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall Research and Development AB, Älvkarleby, Sweden.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Estimating localized pressure fluctuations in Gävunda hydropower tunnel2020In: Proceedings of the 8th IAHR International Symposium on Hydraulic Structures ISHS2020, The University of Queensland , 2020Conference paper (Refereed)
    Abstract [en]

    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.

  • 5.
    Andersson, L. Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, I. A. Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Burman, Anton J.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall Research and Development, Älvkarleby, Sweden.
    Localized roughness effects in non-uniform hydraulic waterways2021In: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 59, no 1, p. 100-108Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Andersson, L. Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall Research and Development, Älvkarleby.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Characterization of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations2018In: Engineering, ISSN 1947-3931, Vol. 10, p. 399-416Article in journal (Refereed)
    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.

  • 7.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Vattenfall Research & Development.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Grade of geometric resolution of a rough surface required for accurate prediction of pressure and velocities in water tunnels2014Conference paper (Refereed)
    Download full text (pdf)
    FULLTEXT01
  • 8.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Burman, Anton
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall Research and Development, Älvkarleby.
    Inlet Blockage Effects in a Free Surface Channel With Artificially Generated Rough Walls2018In: Proceedings of the 7th IAHR International Symposium on Hydraulic Structures / [ed] Daniel Bung ; Blake Tullis, 2018, p. 723-732Conference paper (Refereed)
    Abstract [en]

    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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    fulltext
  • 9.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gävunda case studyManuscript (preprint) (Other academic)
  • 10.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall AB Research and Development, Älvkarleby Laboratory, Älvkarleby.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical investigation of a hydropower tunnel: Estimating localised head-loss using the manning equation2019In: Water, E-ISSN 2073-4441, Vol. 11, no 8, article id 1562Article in journal (Refereed)
    Abstract [en]

    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. 

  • 11.
    Andersson, Robin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental Study of Head Loss over Laser Scanned Rock Tunnel2016In: Experimental Study of Head Loss over Laser Scanned Rock Tunnel: Hydraulic Structures and Water System Management, ISHS 2016, Portland, United States, 27 - 30 June 2016, Portland: Utah State University , 2016, p. 22-29Conference paper (Refereed)
    Abstract [en]

    Flow in hydropower tunnels is characterized by a high Reynolds number and often very rough rock walls. Due to the roughness of the walls, the flow in the tunnel is highly disturbed, resulting in large fluctuations of velocity and pressure in both time and space. Erosion problems and even partial collapse of tunnel walls are in some cases believed to be caused by hydraulic jacking from large flow induced pressure fluctuations. The objective of this work is to investigate the effects of the rough walls on the pressure variations in time and space over the rock surfaces. Pressure measurement experiments were performed in a 10 m long Plexiglas tunnel where one of the smooth walls was replaced with a rough surface. The rough surface was created from a down-scaled (1:10) laser scanned wall of a hydraulic tunnel. The differential pressure was measured at the smooth surface between points placed at the start and end of the first four 2 m sections of the channel. 10 gauge pressure sensors where flush mounted on the rough surface; these sensors measure the magnitude and the fluctuations of the pressure on the rough surface. The measurements showed significant spatial variation of the pressure on the surface. For example, sensors placed on protruding roughness elements showed low gauge pressure but high fluctuations. The differential pressure indicated a head loss through the tunnel that was almost four times higher than a theoretical smooth channel.

  • 12.
    Bin Asad, S M Sayeed
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Leonardsson, Kjell
    Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Wall shear stress measurement on curve objects with PIV in connection to benthic fauna in regulated rivers2019In: Water, E-ISSN 2073-4441, Vol. 11, no 4, article id 650Article in journal (Refereed)
    Abstract [en]

    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.

  • 13.
    Bin Asad, S M Sayeed
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    A Review of Particle Image Velocimetry for Fish Migration2016In: World Journal of Mechanics, ISSN 2160-049X, E-ISSN 2160-0503, Vol. 6, no 4, p. 131-149Article in journal (Refereed)
    Abstract [en]

    Understanding the flow characteristic in fishways is crucial for efficient fish migration. Flow characteristic measurements can generally provide quantitative information of velocity distributions in such passages; Particle Image Velocimetry (PIV) has become one of the most versatile techniques to disclose flow fields in general and in fishways, in particular. This paper firstly gives an overview of fish migration along with fish ladders and then the application of PIV measurements on the fish migration process. The overview shows that the quantitative and detailed turbulent flow information in fish ladders obtained by PIV is critical for analyzing turbulent properties andvalidating numerical results.

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  • 14.
    Bin Asad, S M Sayeed
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Velocity distribution measurements in a fishway like open channel by Laser Doppler Anemometry (LDA)2016In: / [ed] Dancova, P; Vesely, M, 2016Conference paper (Refereed)
    Abstract [en]

    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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  • 15.
    Burman, Anton
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Inherent damping in a partially dry river2019In: E-proceedings of the 38th IAHR World Congress, International Association for Hydro-Enviroment Engineering and Research (IAHR) , 2019, p. 5091-5100Conference paper (Refereed)
    Abstract [en]

    As intermittent power sources such as solar power and wind power gains traction in Scandinavia it is likely that the electricity production will become increasingly dependent on hydro power as a buffer in times of power deficit from intermittent power sources due to weather conditions. Rapid changes in hydro power demand can rapidly change the flow conditions in proximity to the power plant. This paper aims to model the transient behavior and quantify the inherent damping in a dry reach in proximity to the largest hydro power plant in Sweden, with respect to production. A two-dimensional model solving the Navier-Stokes equations with shallow water approximations was set up using the open-source solver Delft3D. The Manning numbers in the reach was calibrated with measured steady state water surface elevation data. The simulation data was then validated with transient water level measurements. The results show that it's possible to calibrate the Manning numbers using steady state water level measurements. The model also shows that it's possible to capture the inherent damping and more transient behavior using Delft3D. The results can be used to better model rivers without the need for resolving the upstream reach. The results can also be used for ecohydraulical applications where the transient behavior is important.

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    fulltext
  • 16.
    Burman, Anton
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Xie, Qiancheng
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ecohydraulical Applications and Limitations of Calibrated Numerical 2D Models2022In: Proceedings of the 39th IAHR World Congress: From Snow To Sea / [ed] Miguel Ortega-Sánchez, International Association for Hydro-Environment Engineering and Research (IAHR) , 2022, p. 1557-1564Conference paper (Refereed)
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    fulltext
  • 17.
    Burman, Anton J.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hydraulic classification of hydropeaking stages in a river reach2023In: Rivers Research and Applications: an international journal devoted to river research and management, ISSN 1535-1459, E-ISSN 1535-1467, Vol. 39, no 4, p. 692-702Article in journal (Refereed)
    Abstract [en]

    Hydropower is an important tool in the struggle for low-emission power production. In the Nordic countries, hydropower operating conditions are expected to change and work more in conjunction with intermittent power production. This in turn might increase the amount of hydropeaking events in the reaches downstream of hydropower plants. The current work investigates the influence of highly flexible, high-frequency hydropeaking on the hydrodynamics in the downstream reach. By quantifying four different dynamic stages in the study reach, the influence of the hydropeaking frequencies was investigated in the bypass reach of the Stornorrfors hydropower plant in the river Umeälven in northern Sweden. The hydrodynamics in the study reach were numerically modelled using the open source solver Delft3D. Eight different highly flexible future hydropeaking scenarios, varying from 12 to 60 flow changes per day, were considered. A method for identifying four hydropeaking stages—dewatering, dynamic, alternating and uniform —was introduced. The hydropeaking frequency directly decided the stage in most of the study reach. Furthermore, a Fourier analysis showed a significant difference between the stages and their corresponding power spectra. The classification of stages put forward in this work provides a novel, simple method to investigate the hydrodynamics due to hydropeaking in a river reach.

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  • 18.
    Burman, Anton J.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Investigating damping properties in a bypass river2020In: River Flow 2020: Proceedings of the 10th Conference on Fluvial Hydraulics (Delft, Netherlands, 7-10 July 2020) / [ed] Wim Uijttewaal; Mário J. Franca; Daniel Valero; Victor Chavarrias; Clàudia Ylla Arbós; Ralph Schielen; Alessandra Crosato, London: Taylor & Francis Group, 2020, p. 2361-2366Conference paper (Refereed)
    Abstract [en]

    The operating conditions of hydropower plants in Sweden are expected to change in the coming decades with potentially many hydropeaking events every day. It is therefor important to understand how inherent damping properties in rivers can be used to mitigate potential negative influences on fluvial ecosystems. The effect of the upstream dam closing time and the Manning number distribution in the reach on the transient behavior of the downstream water level and wetted area is investigated. In the study reach the shallow-water equations are solved using the open-source solver Delft3D. The simulations show that the transient change in water level is mainly dependent on the upstream dam closing time. The dynamics of the wetted area is considerably affected by the closing time of the dam. The Manning number has a negligible effect on the transient behavior for the wetted area and the waterlevel. The results in this study can be used for future ecohydraulical applications such as identifying potential stranding zones.

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  • 19.
    Burman, Anton J.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Angele, Kristian
    Vattenfall Research and Development, Älvkarlebylaboratoriet, 814 70 Älvkarleby, Sweden.
    Case Study of Transient Dynamics in a Bypass Reach2020In: Water, E-ISSN 2073-4441, Vol. 12, no 6, article id 1585Article in journal (Refereed)
    Abstract [en]

    The operating conditions of Nordic hydropower plants are expected to change in the coming years to work more in conjunction with intermittent power production, causing more frequent hydropeaking events. Hydropeaking has been shown to be detrimental to wildlife in the river reaches downstream of hydropower plants. In this work, we investigate how different possible future hydropeaking scenarios affect the water surface elevation dynamics in a bypass reach in the Ume River in northern Sweden. The river dynamics has been modeled using the open-source solver Delft3D. The numerical model was validated and calibrated with water-surface-elevation measurements. A hysteresis effect on the water surface elevation, varying with the downstream distance from the spillways, was seen in both the simulated and the measured data. Increasing the hydropeaking rate is shown to dampen the variation in water surface elevation and wetted area in the most downstream parts of the reach, which could have positive effects on habitat and bed stability compared to slower rates in that region.

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  • 20.
    Burman, Anton J.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hedger, Richard D.
    Norwegian Institute for Nature Research – NINA, NO-7034 Trondheim, Norway.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sundt-Hansen, Line E.
    Norwegian Institute for Nature Research – NINA, NO-7034 Trondheim, Norway.
    Modelling the downstream longitudinal effects of frequent hydropeaking on the spawning potential and stranding susceptibility of salmonids2021In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 796, article id 148999Article in journal (Refereed)
    Abstract [en]

    Hydropower plant operating conditions are expected to change to be more in tandem with intermittent power production so as to meet the requirements of the Paris Agreement, which in turn may negatively impact ecological conditions downstream of the hydropower plants. The current study investigates how highly flexible hydropower operating conditions may impact several salmonid species (European grayling, Atlantic salmon and brown trout) in the River Umeälven, a major river in northern Sweden; specifically, how changes in hydropeaking frequency may affect the area of the downstream watercourse that is hydraulically suitable for spawning (potential spawning area) and how changes in spill gate closing time may affect the propensity to stranding. River hydrodynamics were modeled using the open-source solver Delft3D, with a range of hydropeaking frequencies (from 10 to 60 starts and stops per day) and a range of spill gate closing times from (1–30 min). Increasing the hydropeaking frequency caused a reduction in potential spawning area, but also a reduction in dewatering of potential spawning area at low flows. Increasing spill gate closing time caused a decrease in propensity to stranding. Effects were dependent on both species and life-stage, and declined longitudinally with distance downstream from the spillway outlet. The modelling approach used here provides an effective method for predicting likely outcomes of flexible hydropower operating conditions, taking into account fish species and life-stages present and watercourse characteristics.

  • 21.
    Fabricius, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Miroshnikova, Elena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Wall, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Darcy's law for flow in a periodic thin porous medium confined between two parallel plates2016In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 115, no 3, p. 473-493Article in journal (Refereed)
    Abstract [en]

    We study stationary incompressible fluid flow in a thin periodic porous medium. The medium under consideration is a bounded perforated 3D-domain confined between two parallel plates. The distance between the plates is \(\delta \), and the perforation consists of \(\varepsilon \)-periodically distributed solid cylinders which connect the plates in perpendicular direction. Both parameters \(\varepsilon \), \(\delta \) are assumed to be small in comparison with the planar dimensions of the plates. By constructing asymptotic expansions, three cases are analysed: (1) \(\varepsilon \ll \delta \), (2) \(\delta /\varepsilon \sim \text {constant}\) and (3) \(\varepsilon \gg \delta \). For each case, a permeability tensor is obtained by solving local problems. In the intermediate case, the cell problems are 3D, whereas they are 2D in the other cases, which is a considerable simplification. The dimensional reduction can be used for a wide range of \(\varepsilon \) and \(\delta \) with maintained accuracy. This is illustrated by some numerical examples.

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  • 22.
    Fallahjoybari, Nima
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Maerefat, Mehdi
    Department of Mechanical Engineering, Tarbiat Modares University.
    Nimvari, Majid E.
    Department of Mechanical Engineering, Tarbiat Modares University, Faculty of Engineering Technologies, Amol University of Special Modern Technologies, Amol.
    Numerical Computation of Macroscopic Turbulent Quantities in a Porous Medium: an Extemsion to a macroscopic Turbulent model2016In: Journal of Porous Media, ISSN 1091-028X, E-ISSN 1934-0508, Vol. 19, no 6, p. 497-513Article in journal (Refereed)
    Abstract [en]

    A numerical study is conducted using a standard numerical model for a porous medium consisting of a staggered arrangement of square cylinders. Fully developed macroscopic turbulent kinetic energy and dissipation rate are derived and analyzed for different porosities of the medium at different Reynolds numbers. The results obtained are used to extend the applicability range of an existing macroscopic turbulence model in porous media to low-Reynolds-number turbulent flows. It is shown that the levels of normalized macroscopic turbulent kinetic energy and dissipation rate are not constant over the entire range of Reynolds number. These quantities increase from lower levels at low Reynolds numbers up to an asymptotic value being independent of Reynolds number. The constants in the closure expression of the macroscopic turbulence equations are modified using the present results. Finally, in order to highlight the importance of the present modifications, the results of the macroscopic turbulence model before and after the modifications are compared for two cases.

  • 23.
    Forslund, Tobias O. M.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, I. A. Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    A dual-lattice hydrodynamic-thermal MRT-LBM model implemented on GPU for DNS calculations of turbulent thermal flows2022In: International journal of numerical methods for heat & fluid flow, ISSN 0961-5539, E-ISSN 1758-6585, Vol. 35, no 5, p. 1703-1725Article in journal (Refereed)
    Abstract [en]

    Purpose

    The purpose of this paper is to present a fast and bare bones implementation of a numerical method for quickly simulating turbulent thermal flows on GPUs. The work also validates earlier research showing that the lattice Boltzmann method (LBM) method is suitable for complex thermal flows.

    Design/methodology/approach

    A dual lattice hydrodynamic (D3Q27) thermal (D3Q7) multiple-relaxation time LBM model capable of thermal DNS calculations is implemented in CUDA.FindingsThe model has the same computational performance compared to earlier publications of similar LBM solvers. The solver is validated against three benchmark cases for turbulent thermal flow with available data and is shown to be in excellent agreement.

    Originality/value

    The combination of a D3Q27 and D3Q7 stencil for a multiple relaxation time -LBM has, to the authors’ knowledge, not been used for simulations of thermal flows. The code is made available in a public repository under a free license.

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  • 24.
    Forslund, Tobias O. M.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, I. A. Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    The Effects of Periodicity Assumptions in Porous Media Modelling2021In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 137, no 3, p. 769-797Article in journal (Refereed)
    Abstract [en]

    The effects of periodicity assumptions on the macroscopic properties of packed porous beds are evaluated using a cascaded Lattice-Boltzmann method model. The porous bed is modelled as cubic and staggered packings of mono-radii circular obstructions where the bed porosity is varied by altering the circle radii. The results for the macroscopic properties are validated using previously published results. For unsteady flows, it is found that one unit cell is not enough to represent all structures of the fluid flow which substantially impacts the permeability and dispersive properties of the porous bed. In the steady region, a single unit cell is shown to accurately represent the fluid flow across all cases studied

  • 25.
    Forslund, Tobias O. M.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, I. A. Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Non-Stokesian flow through ordered thin porous media imaged by tomographic-PIV2021In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 62, no 3, article id 46Article in journal (Refereed)
    Abstract [en]

    The 3D flow-fields in a staggered and cubic arrangement of mono-radii cylinders are investigated using tomographic-PIV. The cylinder Reynolds-number is in the range of ≈10 to ≈800 giving an almost complete overview of the transition region. Two pore-scale effects are discovered. The first, visible in the cubic packing, is a spatially alternating lateral velocity field, which has a significant impact on the pressure drop and transversal dispersion. The second effect, present in the staggered array, is an example of a disturbance propagation effect that takes place in the laminar steady region; this manifests as a peculiar and complex flow-pattern. In accordance with other studies, it is shown that Darcy’s law can, from an engineering point of view be valid far beyond the limit for Stokesian flow.

  • 26.
    Forslund, Tobias O.M.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, I. A. Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Steady-State Transitions in Ordered Porous Media2023In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 149, no 2, p. 551-577Article in journal (Refereed)
    Abstract [en]

    Previously performed experiments on flow through an ordered porous media cell with tomographic particle image velocimetry reveal a complex three-dimensional steady-state flow pattern. This flow pattern emerge in the region where inertial structures have been previously reported for a wide range of packings. The onset of these steady-state inertial flow structures is here scrutinized for three different types of packing using a finite difference method. It is concluded that the onset of the flow structure coincides with a symmetry break in the flow field and discontinuities in the pressure drop, volume averaged body forces and heat transfer. A quantity for identifying the transition is proposed, namely the pressure integral across the solid surfaces. It is also shown that the transition can both increase and decrease the heat transfer dependent on the actual geometry of the porous medium.

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  • 27. Frishfelds, Vilnis
    et al.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Flow-induced deformation of non-crimp fabrics during composites manufacturing2009In: Proceedings of ITP2009: Interdisciplinary Transport Phenomena VI: Fluid, Thermal, Biological, Materials and Space Sciences, October 4-9, 2009, Volterra, Italy, 2009, article id ITP-09-52Conference paper (Refereed)
    Abstract [en]

    Flow induced alteration in permeability of deformable systems of fibres is studied. Low Reynolds number transversal flow through random arrays of aligned cylinders is considered by using a combined methodology of directly solving the twodimensional Navier-Stokes equations for the flow in the vicinity of a single fibre and minimisation of the dissipation rate in a system of fibres. The permeability of large random arrays increases always which is most apparent for compact systems with equal sized fibres. The permeability can also decrease but then for structured or small systems. The elastic deformations of fibre bundles are calculated basing microscopic fibre structure.

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  • 28.
    Frishfelds, Vilnis
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Faculty of Physics and Mathematics, University of Latvia, Zellu 8, Riga, LV-1002, Latvia.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mattsson, Hans
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Fluid Flow Induced Deformation of Porous Medium, Modeling of Theno Erosion Filter Test Experiment2010In: Proceedings of the 3rd International Conference on Porous Media and its Applications in Science and Engineering: ICPM3, 2010Conference paper (Refereed)
    Abstract [en]

    To study internal erosion in depth it is necessary to know either the detailed flow or how it varies in a statistical manner. It is also important to know how the internal erosion process initiates and progresses due to the fluid flow-induced forces. The underlying reason for this is that internal erosion will initiate exactly where the forces from the fluid are higher than the retaining forces that keep the particles together. Hence, a new model is here developed where fluid flow induced deformations of a large number of particles is studied. The model is applied to the No Erosion Filter test and simulated results resemble experimental results from the literature. The NEF test is used to investigate parameters such as the hydraulic conductivity and also in detail the process of internal erosion. The simulations are performed on different set-ups to exemplify successful and unsuccessful sealing. In the model, minimization of the dissipation rate of energy is accompanied with discretization of the system with modified Voronoi diagrams. Then Computational Fluid Dynamics is applied to solve the flow within each part of the Voronoi diagrams. Different parameters, such as the vorticity, calculated with the CFD-software are then used as input to the Monte Carlo-simulations. An overall good conformity between simulated results and experimental results from the literature is obtained.

  • 29.
    Frishfelds, Vilnis
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Alteration of permeability caused by transversal flow-induced deformation of fibres during composites manufacturing2010In: Proceedings of The 10th International Conference on Flow Processes in Composite Materials (FPCM10): Monte Verità, Ascona, CH – July 11-15, 2010, 2010Conference paper (Refereed)
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  • 30.
    Frishfelds, Vilnis
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Flow-induced deformations within random packed beds of spheres2014In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 104, no 1, p. 43-56Article in journal (Refereed)
    Abstract [en]

    Low Reynolds number flow-induced alterations of permeability of random packing of mono-sized spheres is studied. The number of spheres is several thousands and the porosities ranges between 0.4 and 0.6. The change of permeability is obtained for elastic deformations of the positions of the spheres using either of two methods. Each sphere is elastically attached to single points or the spheres that are connected via an elastic porous network. The system of spheres is divided into smaller volumes with Voronoi diagrams and the flow is derived by usage of a dual stream function. The local saturated flow fields are approximated as for close packed spheres and the overall flow pattern is obtained by minimising the dissipation rate of energy. The results show that the permeability for large random systems increases as a function of velocity and thus the deformation. The alteration is, however, much less than for two-dimensional cases like parallel cylinders. The relative increase in permeability becomes larger as the porosity increases from 0.4 to 0.6.

  • 31.
    Frishfelds, Vilnis
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mattsson, Hans
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Fluid flow induced internal erosion within porous media: modelling of the no erosion filter test experiment2011In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 89, no 3, p. 441-457Article in journal (Refereed)
    Abstract [en]

    An investigation of the potential to numerically model the no erosion filter test is performed here, where the flow through a large ensemble of particles is considered by applying minimisation of dissipation rate of energy on the ensemble that is discretised with modified Voronoi diagrams and Delaunay triangulation. Low-Reynolds number simulations are applied to each part of the Voronoi diagram using computational fluid dynamics. The mechanical friction between particles is modelled by increasing the effective viscosity for closely spaced particles. Microscopic mechanisms for successful and unsuccessful sealing of filters are obtained. The numerical results agree with previously presented experimental observations by Sherard and Dunnigan. A conformity is that the sealing starts from the end of the channel and continues outwards in the radial direction. The sealing implies that the permeability can be reduced several orders of magnitude during a test.

  • 32.
    Gebart, Rikard
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Bengtsson, Per-Erik
    Lund University.
    Schmidt, Florian
    Umeå University.
    Wiinikka, Henrik
    RISE-ETC.
    Broström, Markus
    Umeå University.
    Backman, Rainer
    Umeå University.
    Carlborg, Markus
    Umeå University.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Umeki, Kentaro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Weiland, Fredrik
    RISE-ETC.
    SFC – Annual Summary from Bio4Gasification (B4G)2020Report (Other (popular science, discussion, etc.))
  • 33.
    Ghasemi Monfared, Zahra
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Umeki, Kentaro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    The Impact of Discrete Element Method Parameters on Realistic Representation of Spherical Particles in a Packed Bed2024In: Processes, E-ISSN 2227-9717, Vol. 12, no 1, article id 183Article in journal (Refereed)
    Abstract [en]

    Packed bed reactors play a crucial role in various industrial applications. This paper utilizes the Discrete Element Method (DEM), an efficient numerical technique for simulating the behavior of packed beds of particles as discrete phases. The focus is on generating densely packed particle beds. To ensure the model accuracy, specific DEM parameters were studied, including sub-step and rolling resistance. The analysis of the packed bed model extended to a detailed exploration of void fraction distribution along radial and vertical directions, considering the impact of wall interactions. Three different samples, spanning particle sizes from 0.3 mm to 6 mm, were used. Results indicated that the number of sub-steps significantly influences void fraction precision, a key criterion for comparing simulations with experimental results. Additionally, the study found that both loosely and densely packed beds of particles could be accurately represented by incorporating appropriate values for rolling friction. This value serves as an indicator of both inter-particle friction and friction between particles and the walls. An optimal rolling friction coefficient has been thereby suggested for the precise representation for the densely packed bed of spherical char particles.

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  • 34.
    Hadi Jafari, Pantea
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    On the Influence from Turbulence Modeling on Particle Suspension Flow in Cyclone Gasifiers2014Conference paper (Refereed)
    Abstract [en]

    Air-blown cyclone gasification is an entrained flow gasification process in which biomass powder fuel is burnt in a gasifier that operates similarly to a cyclone separator. Cyclone separators are widely used in industry to separate a dispersed solid phase (e.g. particles) from a continuous flow of gas based on density differences. Due to its simple design, the cyclone is a reliable apparatus with low cost for manufacture and maintenance.The performance of an isothermal cyclone separator can be predicted satisfactorily with the model developed by Muschelknautz et al. However, the flow in a non-isothermal cyclone gasifier has additional complexities, e.g. the production of gas from the fuel particles, that are outside the scope of the Muschelknautz model. In order to incorporate these effects more advanced modeling based on Computational Fluid Dynamics is needed. One problem with the CFD approach in combination with turbulent heat transfer and chemical reactions is that the complexity of the global model makes it difficult to assess the accuracy of the sub-models. Recently published models are based on relatively simple eddy-viscosity turbulence models. The agreement between these models and experiments has been encouraging but one cannot rule out the possibility that the apparently good performance of the model is a lucky coincidence due to cancellation of errors in the different sub models.The present paper is focusing on the fluid dynamics modeling of the flow in a cyclone gasifier in order to develop a better foundation for continued modeling. Since simulation of dispersed phase behavior is based on a precise modeling of the continuous phase flow field, it is valuable to assess different numerical approaches to find the most promising one for simulating the turbulent gas phase flow. Due to the complexity of turbulent swirling flow in a cyclone gasifier, a careful selection of turbulence models is needed to fulfill accurate numerical calculations of flow parameters. Two families of turbulence models are supposed to be tested: the two-equation eddy viscosity models including k-epsilon and k-omega, and the Reynolds stress model. For the k-epsilon model, steady-state and transient simulations are implemented. The gas cyclone of Obermair et al. with relevant operating conditions was chosen as a benchmark. The simulation results are compared to the Laser Doppler Anemometry (LDA) velocity measurements of the gas cyclone. The simulations are implemented in the commercial CFD (computational fluid dynamics) code ANSYS CFX 14.5; which uses an element-based finite volume approach. The method involves discretization of the spatial domain using a three-dimensional mesh to build up finite volumes over which relevant quantities like mass, momentum, and energy are conserved. In all, the capability of the mentioned approaches for representing the flow field in general and the precessing vortex core and its related fluctuations in particular will be discussed.

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  • 35.
    Hadi Jafari, Pantea
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Turbulence Modelling of a Single-Phase Flow Cyclone Gasifier2017In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, no 9, p. 779-799, article id 79329Article in journal (Refereed)
    Abstract [en]

    The current work aims to make a foundation for an engineering design of a cyclone gasifier to be able not only to predict its flow field with a suitable accuracy but also to investigate a large number of design alternatives with limited computer resources. A good single-phase flow model that can form the basis in an Euler-Lagrange model for multi-phase flow is also necessary for modelling the reacting flow inside a cyclone gasifier. The present paper provides an objective comparison between several popular turbulence modelling options including standard k-ε and SST with curvature corrections, SSG-RSM and LES Smagorinsky models, for the single-phase flow inside cyclone separators/gasifiers that can serve as a guide for further work on the reacting multi-phase flow inside cyclone gasifiers and similar devices. A detailed comparison between the models and experimental data for the mean velocity and fluctuating parts of the velocity profiles are presented. Furthermore, the capabilities of the turbulence models to capture the physical phenomena present in a cyclone gasifier that affects the design process are investigated.

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    Turbulence Modelling of a Single-Phase Flow Cyclone Gasifier
  • 36.
    Hadi Jafari, Pantea
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Misiulia, Dzmitry
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Modeling of Particle-Laden Cold Flow in a Cyclone Gasifier2018In: Journal of Fluids Engineering, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 141, no 2, article id 021302Article in journal (Refereed)
    Abstract [en]

    Isothermal transient Eulerian–Lagrangian simulation of the turbulent gas–solid flow in a cyclone gasifier with two inlet tubes at 890 °C has been performed. The single-phase gas flow is modeled using SSG Reynolds stress turbulence model. Ten thousand representative solid particles of different sizes are injected from each inlet continuously at every second of simulation time. Particles are finally stopped as soon as they arrive at the outlet or reach the bottom plate of the gasifier. The effect of particle-to-gas coupling on the pressure and velocity of the flow and particles motion inside the gasifier is studied. The numerical approach can reasonably predict the impact of particle load on the gas flow as presented in the experimental results. Single particles are traveled throughout the transient gas flow field by using Lagrangian approach. High temperature of the gas flow inside the gasifier has significant effects on the swirl intensity reduction, damping the turbulence in the core region, pressure, and particle behaviors. However, the presence of solid particles does not have a notable influence on the swirl intensity and turbulence.

  • 37.
    Hadi Jafari, Pantea
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Numerical Simulation of Biomass Gasification in an Entrained Flow Cyclone Gasifier2020In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 34, no 2, p. 1870-1882Article in journal (Refereed)
    Abstract [en]

    A transient, two-way coupled Eulerian−Lagrangian computational fluid dynamics model has been developed for numerically investigating the gasification process of wood powder inside a cyclone-shaped reactor. The suggested model has considered heat and mass transfer, drying, devolatilization, and homogeneous and heterogeneous reactions. The model is validated using the experimental data from a commercial entrained-flow cyclone gasifier. The changes in gas composition as a function of equivalence ratio and the behavior of gasification process agreed well with the experimental measurement. Trajectories of individual particles were captured, and the behavior, mass fraction, and temperature distribution of several representative particles in different sizes were studied. Moreover, the model was successful in prediction of produced gas lower heating value, cold gas efficiency, and carbon conversion.

  • 38.
    Hadi Jafari, Pantea
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Wingren, Anders
    Meva Energy AB, Hisings Backa.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Effect of process parameters on the performance of an air-blown entrained flow cyclone gasifier2020In: International Journal of Sustainable Energy, ISSN 1478-6451, E-ISSN 1478-646X, Vol. 39, no 1, p. 21-40Article in journal (Refereed)
    Abstract [en]

    Entrained flow gasification of biomass in a cyclone reactor combined by a gas engine has been applied in Nordic countries as one of the preferred methods for generating combined heat and power in small scales. The purpose of the current study was to optimise the gasification plant efficiency and understanding the influence of operating conditions. The experiments were carried out in a 2.4 MW(th) commercial gasification power plant. The gasifier was operated in optimum at a rather low lambda around 0.27 and a temperature of 950°C. The lower heating value of the clean product gas at this lambda was 5.95 MJ/Nm3. The experimental results also were compared with the predicted values from thermodynamic equilibrium calculations by Factsage 7.0. The performance of five different types of biofuels including torrefied spruce, peat, rice husk, bark and stemwood were assessed and compared with each other using thermodynamic equilibrium and available experimental data.

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  • 39.
    Hang, Trieu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Bergström, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Vattenfall.
    Image-based river surface velocimetry: considerations from a case studyManuscript (preprint) (Other academic)
  • 40.
    Hang, Trieu
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Bergström, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall, Research & Development Hydraulic Laboratory, 81426 Älvkarleby, Sweden.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Photogrammetry for Free Surface Flow Velocity Measurement: From Laboratory to Field Measurements2021In: Water, E-ISSN 2073-4441, Vol. 13, no 12, article id 1675Article in journal (Refereed)
    Abstract [en]

    This study describes a multi-camera photogrammetric approach to measure the 3D velocityof free surface flow. The properties of the camera system and particle tracking velocimetry (PTV)algorithm were first investigated in a measurement of a laboratory open channel flow to prepare forfield measurements. The in situ camera calibration methods corresponding to the two measurementsituations were applied to mitigate the instability of the camera mechanism and camera geometry.There are two photogrammetry-based PTV algorithms presented in this study regarding differenttypes of surface particles employed on the water flow. While the first algorithm uses the particletracking method applied for individual particles, the second algorithm is based on correlation-basedparticle clustering tracking applied for clusters of small size particles. In the laboratory, referencedata are provided by particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). Thedifferences in velocities measured by photogrammetry and PIV, photogrammetry and LDV are 0.1%and 3.6%, respectively. At a natural river, the change of discharges between two measurement timesis found to be 15%, and the corresponding value reported regarding mass flow through a nearbyhydropower plant is 20%. The outcomes reveal that the method can provide a reliable estimation of3D surface velocity with sufficient accuracy.

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  • 41.
    Hatem, Mohammed
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Pusch, Roland
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Knutsson, Sven
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Rheological Properties of Cement-Based Grouts Determined by Different Techniques2014In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 6, no 5, p. 217-229Article in journal (Refereed)
    Abstract [en]

    The rheological properties of cement-based grouts containing talc or palygorskite were investigated for optimizing fluidity and quick strengthening at injection. The fluidity controls the ability of grout to penetrate fractures and can be determined by pipe flow tests, Marsh funnel tests, mini-slump cone tests and rheometer tests. The grouts were 1) Talc for fluidity and strength by reacting with cement, 2) Palygorskite (attapulgite) for early gelation by being thixotropic, and 3) Powdered quartz for chemical integrity. The freshly prepared grouts behaved as Bingham fluids with viscosities from 0.151 to 0.464 Pas and yield stresses 5.2 Pa to 36.7 Pa. Statistical analysis of the flow test data converted Marsh flow time into viscosity. The pipe flow tests gave 26.5% higher values than the viscometer for grout with Portland cement and talc, and about 13.7% lower than the viscometer data for the grout with low-pH cement and talc. The big Marsh funnel gave valuesdiffering by 5.2% - 5.3% from those of the viscometer for grout with talc and Portland, and Merit 5000 cements. For grout with palygorskite the viscosity was at least twice that of the other grouts. Grout fluidity was positively affected by talc and negatively by palygorskite and early cement hydration

  • 42.
    Hazim, Ammar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Turbulent modulation in particulate flow: A review of critical variables2015In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 7, no 10, p. 597-609, article id 8102444Article in journal (Refereed)
    Abstract [en]

    A review of the main mechanisms influencing turbulent modulation in the presence of spherical and non-spherical particles is presented. The review demonstrates the need for more numerical and experimental work with higher accuracy than obtained so far and the need to resolve the flow near the surface of particles with the aim to re-evaluate the quantitative effect of different parameters on turbulent modulation. The review reveals that non-spherical particles have more adverse effect on turbulence as compared to spherical ones, for the same ambient conditions

  • 43.
    Hazim, Ammar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental study of the effect from bio-solid particles on fully developed turbulent duct flow2014Conference paper (Refereed)
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  • 44.
    Hedberg, P. A. Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andreasson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Vattenfall Research and Development, Älvkarleby, Sweden.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Angele, K.
    Vattenfall Research and Development, Älvkarleby, Sweden .
    Andersson, L. Robin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical modelling of flow in parallel spillways2020In: Proceedings of the 8th IAHR International Symposium on Hydraulic Structures ISHS2020, The University of Queensland , 2020Conference paper (Refereed)
    Abstract [en]

    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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  • 45.
    Hedberg, P. A. Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Solheim, Nils
    Norwegian University of Science and Technology, 2, Trondheim, Norway.
    Experimental and computational evaluation of fish passageway with porous media boundary2023In: Proceedings of the 40th IAHR World Congress - 2023: Rivers - Connecting Mountains and Coasts / [ed] Helmut Habersack; Michael Tritthart; Lisa Waldenberger, International Association for Hydro-Environment Engineering and Research (IAHR) , 2023, p. 2422-2428Conference paper (Refereed)
  • 46.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Parallel computing of fluid flow through porous media2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fluid flow through porous media takes place in a variety of technical areas including ground water flow, flow through embankment dams, paper making, composites manufacturing, filtering, drying and sintering of iron ore pellets. When modelling these kinds of flows it is common practice to use averaging techniques rather than computing the detailed flow field in every single pore. This approach is very efficient when averaged quantities are sough for but it is not very convenient for local problems such as forces on particles within an embankment dam and drying of individual iron ore pellets. In this thesis the focus is set on the former and how such forces alter as a function of Reynolds number. Of particular interest are the effects of inertia and turbulence and when they need to be considered. For problem like this a Computational Fluid Dynamics (CFD) approach is well suited since rather complex geometries and flow conditions can be studied by using parallel computing techniques. By using this technique it is also possible to determine at which flow regimes Darcy law is applicable and thus when more elaborate descriptions of the flow like the Forchheimer equation and the Navier-Stokes equations need to be applied. In order to isolate the question above and be able to use advanced models for turbulence a neat geometry is applied being an array of quadratic packed cylinders. To start with the parallel computing capacity of the in-house cluster is scrutinized showing very promising results with up to almost full scalability. Following this study focus is set on the porous media and when inertia-effects need to be taken into account. The significance of this phenomenon turns out to be when Reynolds number is above 10. Then a study in when the flow has to be solved with a full turbulent description has been carried out with the results that as the Reynolds number increases above 100 the significance is clear. In addition a manuscript for a state of the art literature survey is appended.

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  • 47.
    Hellström, Gunnar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Leonardsson, Kjell
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Lycksam, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundqvist, Hans
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Simulation and experiments of entrance flow conditions to a fishway2016Conference paper (Refereed)
    Abstract [en]

    When migrating fish tries to pass around man made obstacles such as hydropower dams with the aid of fish passages it is important that the migrating path is constructed in an efficient manner. By designing the entrance of the fishway in a manner that gives attractive flow conditions for migrating fish, the overall passage efficiency can be increased. In this study two alternative design solutions have been studied with numerical simulations, lab-scale experiments and in-field testing to achieve such attractive flow. Designs studied are constructions yielding a submerged jet, in order to increase the velocity of the flow at the entrance, and a half-cylinder, in order to create vortices that the fishes can utilize when continuing their journey towards their spawning grounds. A combination of the previous mentioned setups was also investigated. A first result shows that the increase in velocity decreases the residence time downstream the fishway and increases the total passage efficiency while the result from the vorticity generation is inconclusive at this point. The combination of the two designs shows similar passage efficiency as with only velocity increase although it does not show the same decrease in residence time. Improvements on the design of the vorticity generator and shape optimization of the construction generating the jet could further improve the efficiency of the fishway

  • 48. Hellström, Gunnar
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Flow through porous media at moderate Reynolds number2006In: Proceedings, 4th International Scientific Colloquium Modelling for Material Processing, 2006, p. 129-134Conference paper (Refereed)
    Abstract [en]

    In modelling of flow through porous media inertia-effects must sometimes be considered. This is often done by usage of the empirically derived Ergun equation that can describe the response of several porous media but does not reveal the real mechanisms for the flow. In order to increase the understanding of such flows we have therefore performed a micromechanically based study of moderate Re' flow between parallel cylinders using a Computational Fluid Dynamics approach. The simulations are carried out with quality and trust by using grid refinement techniques and securing that the iteration error is sufficiently small. Main results are that the Ergun equation fits well to simulated data up to Re' 20, that inertia-effects must be taken into account when Re' exceeds 10 and that results from stationary simulations replicate time resolved ones at least up to Re' 880.

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  • 49.
    Hellström, Gunnar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, Daniel
    Lundström, Staffan
    Parallel CFD simulations of an original and redesigned hydraulic turbine draft tube2007In: Advances in Engineering Software, ISSN 0965-9978, E-ISSN 1873-5339, Vol. 38, no 5, p. 338-344Article in journal (Refereed)
    Abstract [en]

    The design of hydraulic turbine draft tubes has traditionally been based on simplified analytic methods, model and full-scale experiments. In the recent years the use of numerical methods such as computational fluid dynamics (CFD) has increased in the design process, due to the rapid escalation in computer performance. Today with parallel computer architectures, new aspects of flow can be considered. However, several problems have still to be solved before CFD can routinely be applied in product development. This paper aims to investigate the parallel performance of commercial CFD software on homogeneous computer networks, as common solutions encountered in the industry today. In addition, the efficiency improvements obtained in earlier experiments by modifying the shape of the draft tube will be considered, to deduce if the improvements can be captured with aid of CFD. Results from both the steady and the unsteady CFD simulations show that almost full scalability is obtained with the commercial CFD software CFX-5.7.1. Furthermore, no noticeable improvement in the pressure recovery factor or the flow field is noticed in the CFD simulations as compared to experiments. The discrepancy may be to the applied inlet boundary conditions and/or the turbulence model.

  • 50.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Internal erosion in embankment dams: fluid flow through and deformation of porous media2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A basic understanding of fluid flow through a porous media facilitates a comprehensive understanding of internal erosion in embankment dams. Hence, it is necessary to reveal the detailed seepage flow, the flow-induced forces acting within the porous media and the fluid flow deformation of the porous media. In order to increase the knowledge of the fluid flow a Computational Fluid Dynamics approach is applied to investigate different flow regimes. The regimes ranges from creeping flow, where a Darcy law formulation is sufficient, via an inertia dominated region, where a non-linear term must be added to the Darcy's law such as the Ergun equation, to the turbulent region, where the full Navier-Stokes equations must be solved including a Reynolds decomposition. Since it is not obvious when these transitions takes place the CFD-simulations are used to calculate the apparent permeability, the Blake-type friction factor and the normal and shear forces for a variety of model geometries. This includes quadratic and hexagonal packing of cylinders as well as spheres. One result is that the Reynolds number, where inertia-effects become significant, varies with the packing and the porosity. For a quadratic arrangement of cylinders this occurs around a Reynolds number about 10 while for a hexagonal arrangement it takes place between 30 and 50 depending on the porosity. Another result is that for quadratic arrangement the turbulent set-up at high Reynolds number gives higher forces than a corresponding laminar set-up regardless of the porosity. For hexagonal packing a turbulent set-up can, however, give lower forces. These ranges, regarding the Reynolds number, have been utilized in order to develop an expression for theoretical limits of the effective diameter and the applied pressure gradient to be applied when designing down-scaled geotechnical experimental setups. Regarding the deformation of the porous media there are several methods that has the potential to model the internal erosion process. One way is a mesh deformation approach where the normal and shear forces acting on the particles generate the motion. This methodology requires that the computational mesh is upgraded in every time-step resulting in rather computational heavy simulations. Another way is to combine CFDsimulations of flow in the vicinity of single particles with Monte-Carlo simulations of a system of a large number of particles by using the fact that the distribution of the stream function follows the known principle of minimal dissipation rate of energy. Main result is that the more compact the system is the larger is the possible relative change of permeability by applying a high flow rate. When applying this technique on a classical geotechnical experimental setup, the No Erosion Filter test, results indicate that the developed model captures the main characteristics of the sought particle transportation, both for a sealing as well as a non-sealing design of the filter and fine combination.

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