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Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
• 1.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Modelling and validation of flow over a wall with large surface roughness2012Konferansepaper (Fagfellevurdert)
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FULLTEXT01
• 2.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Effect of spatial resolution of rough surfaces on numerically computed flow fields with application to hydraulic engineering2014Inngår i: Engineering Applications of Computational Fluid Mechanics, ISSN 1994-2060, E-ISSN 1997-003X, Vol. 8, nr 3, s. 373-381Artikkel i tidsskrift (Fagfellevurdert)

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.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies. Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
Describing fish passage in a river confluence with telemetry and CFD2016Inngår i: / [ed] Webb, JA, Costelloe, JF, CasasMulet, R, Lyon, JP, Stewardson, MJ, Melbourne: University of Melbourne , 2016Konferansepaper (Fagfellevurdert)

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.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall Research and Development, Älvkarleby. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Characterization of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations2018Inngår i: Engineering, ISSN 1947-3931, Vol. 10, s. 399-416Artikkel i tidsskrift (Fagfellevurdert)

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.

• 5.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall Research & Development. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Grade of geometric resolution of a rough surface required for accurate prediction of pressure and velocities in water tunnels2014Konferansepaper (Fagfellevurdert)
Fulltekst (pdf)
FULLTEXT01
• 6.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall Research and Development, Älvkarleby.
Inlet Blockage Effects in a Free Surface Channel With Artificially Generated Rough Walls2018Inngår i: Proceedings of the 7th IAHR International Symposium on Hydraulic Structures / [ed] Daniel Bung ; Blake Tullis, 2018, s. 723-732Konferansepaper (Fagfellevurdert)

When considering free surface flow in channels, it is essential to have in-depth knowledge about the inlet flow conditions and the effect of surface roughness on the overall flow field. Hence, we hereby investigate flow inside an 18m long channel by using Particle Tracking Velocimetry (PTV) and Acoustic Doppler Velocimetry (ADV). The roughness of the channel walls is generated using a diamond-square fractal algorithm and is designed to resemble the actual geometry of hydropower tunnels. Four different water levels ranging from 20 to 50cm are investigated. For each depth, the inlet is blocked by 25 and 50% at three positions each, at the centre, to the right and to the left in the flow-direction. The flow is altered for each depth to keep the flow velocity even throughout the measurements. PTV is applied to measure the velocity of the free water surface; four cameras are placed above the setup to capture the entirety of the channel. The results show a clear correlation between roughness-height and velocity distribution at depths 20-30 cm. The surface roughness proved effective in dispersing the subsequent perturbations following the inlet blockage. At 50cm, perturbations from the 50% blockage could be observed throughout the channel. However, at 20cm, most perturbations had subsided by a third of the channel length. The ADV was used to capture the velocity in a total of 375 points throughout the channel, at a depth of 50 cm with no inlet perturbations.

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• 7.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Gävunda case studyManuskript (preprint) (Annet vitenskapelig)
• 8.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall AB Research and Development, Älvkarleby Laboratory, Älvkarleby. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Numerical investigation of a hydropower tunnel: Estimating localised head-loss using the manning equation2019Inngår i: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 11, nr 8, artikkel-id 1562Artikkel i tidsskrift (Fagfellevurdert)

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.

• 9.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Experimental Study of Head Loss over Laser Scanned Rock Tunnel2016Inngår i: 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, s. 22-29Konferansepaper (Fagfellevurdert)

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.

• 10.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall Research and Development, Älvkarleby.
Localised roughness effects in non-uniform hydraulic waterwaysInngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079Artikkel i tidsskrift (Fagfellevurdert)

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.

• 11.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. 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 rivers2019Inngår i: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 11, nr 4, artikkel-id 650Artikkel i tidsskrift (Fagfellevurdert)

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.

• 12.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
A Review of Particle Image Velocimetry for Fish Migration2016Inngår i: World Journal of Mechanics, ISSN 2160-049X, E-ISSN 2160-0503, Vol. 6, nr 4, s. 131-149Artikkel i tidsskrift (Fagfellevurdert)

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.

Fulltekst (pdf)
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• 13.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Velocity distribution measurements in a fishway like open channel by Laser Doppler Anemometry (LDA)2016Inngår i: / [ed] Dancova, P; Vesely, M, 2016Konferansepaper (Fagfellevurdert)

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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• 14.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
Darcy's law for flow in a periodic thin porous medium confined between two parallel plates2016Inngår i: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 115, nr 3, s. 473-493Artikkel i tidsskrift (Fagfellevurdert)

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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• 15.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Department of Mechanical Engineering, Tarbiat Modares University. 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 model2016Inngår i: Journal of Porous Media, ISSN 1091-028X, E-ISSN 1934-0508, Vol. 19, nr 6, s. 497-513Artikkel i tidsskrift (Fagfellevurdert)

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.

• 16.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Investigation of thermal dispersion and intra-pore turbulent heat flux in porous media2020Inngår i: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 81, artikkel-id 108523Artikkel i tidsskrift (Fagfellevurdert)

In the present study, the importance of the thermal dispersion and the turbulent heat flux in porous media and their effects on the macroscopic distribution of thermal energy are investigated. To this end, turbulent flow and heat transfer within five unit-cells mimicking porous media are solved using large eddy simulation. It is shown that the thermal dispersion and the turbulent heat flux are negligible as compared to the convection term in the macroscopic energy equation. When further scrutinizing this equation, it is revealed that except for the longitudinal components of the thermal dispersion, the other components of thermal dispersion and turbulent heat flux may be neglected away from the boundaries as compared to the interfacial heat transfer. Visualizations of vortices show that the size of the turbulence structures within the cells is of the same order as the size of the pores; therefore, the turbulent heat flux is limited to the intra-pore level. Finally, a discussion is provided on the accuracy of the gradient type diffusion model commonly used for turbulent heat flux in porous media in the absence of macroscopic turbulence. It is shown that the intra-pore turbulence does not affect the macroscopic transport of thermal energy within the porous media studied.

• 17.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Investigation of Hydrodynamic Dispersion and Intra-pore Turbulence Effects in Porous Media2020Inngår i: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 131, nr 2, s. 739-765Artikkel i tidsskrift (Fagfellevurdert)

The aim of the present paper is to evaluate and compare the pore level hydrodynamic dispersion and effects of turbulence during flow in porous media. In order to compute these quantities, large eddy simulations of turbulent flow in five unit cells comprised of spherical particles are performed and the results are averaged over the cells. Visualizations of vortical structures reveal that the size of the turbulence structures is of the size of the pores. Investigations furthermore yield that volume-averaged values of the hydrodynamic dispersion are of the same order as the Reynolds stress within the pores. It is also shown that the effect of intra-pore turbulence and hydrodynamic dispersion on the redistribution of macroscopic momentum within the porous medium is negligible compared to Forchheimer term. A discussion is provided on the accuracy of the eddy viscosity hypothesis in the modeling of the volume-averaged intra-pore Reynolds stresses. Finally, the effect of variation in the pore-scale geometry on the turbulence structures and averaged values of hydrodynamic dispersion and Reynolds stress is investigated.

• 18. Frishfelds, Vilnis
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Flow-induced deformation of non-crimp fabrics during composites manufacturing2009Inngår i: Proceedings of ITP2009: Interdisciplinary Transport Phenomena VI: Fluid, Thermal, Biological, Materials and Space Sciences, October 4-9, 2009, Volterra, Italy, 2009, artikkel-id ITP-09-52Konferansepaper (Fagfellevurdert)

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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• 19. Frishfelds, Vilnis
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
Fluid flow induced deformation of porous medium: modeling of the no erosion filter test experiment2010Inngår i: Proceedings of the 3rd International Conference on Porous Media and its Applications in Science and Engineering: ICPM3, 2010Konferansepaper (Fagfellevurdert)

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.

• 20.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Alteration of permeability caused by transversal flow-induced deformation of fibres during composites manufacturing2010Inngår i: Proceedings of The 10th International Conference on Flow Processes in Composite Materials (FPCM10): Monte Verità, Ascona, CH – July 11-15, 2010, 2010Konferansepaper (Fagfellevurdert)
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• 21.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Flow-induced deformations within random packed beds of spheres2014Inngår i: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 104, nr 1, s. 43-56Artikkel i tidsskrift (Fagfellevurdert)

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.

• 22.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
Fluid flow induced internal erosion within porous media: modelling of the no erosion filter test experiment2011Inngår i: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 89, nr 3, s. 441-457Artikkel i tidsskrift (Fagfellevurdert)

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.

• 23.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Lund University. Umeå University. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. Umeå University. Umeå University. Umeå University. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
SFC – Annual Summary from Bio4Gasification (B4G)2020Rapport (Annet (populærvitenskap, debatt, mm))
• 24.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
On the Influence from Turbulence Modeling on Particle Suspension Flow in Cyclone Gasifiers2014Konferansepaper (Fagfellevurdert)

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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• 25.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Turbulence Modelling of a Single-Phase Flow Cyclone Gasifier2017Inngår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, nr 9, s. 779-799, artikkel-id 79329Artikkel i tidsskrift (Fagfellevurdert)

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
• 26.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Modeling of Particle-Laden Cold Flow in a Cyclone Gasifier2018Inngår i: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 141, nr 2, artikkel-id 021302Artikkel i tidsskrift (Fagfellevurdert)

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.

• 27.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Numerical Simulation of Biomass Gasification in an Entrained Flow Cyclone Gasifier2020Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 34, nr 2, s. 1870-1882Artikkel i tidsskrift (Fagfellevurdert)

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.

• 28.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Meva Energy AB, Hisings Backa. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Effect of process parameters on the performance of an air-blown entrained flow cyclone gasifier2020Inngår i: International Journal of Sustainable Energy, ISSN 1478-6451, E-ISSN 1478-646X, Vol. 39, nr 1, s. 21-40Artikkel i tidsskrift (Fagfellevurdert)

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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• 29.
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Rheological Properties of Cement-Based Grouts Determined by Different Techniques2014Inngår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 6, nr 5, s. 217-229Artikkel i tidsskrift (Fagfellevurdert)

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

• 30.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Influence of Inertial Particles on Turbulence Characteristics in Outer and Near Wall Flow as Revealed with High Resolution PIV2016Inngår i: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 138, nr 9, artikkel-id FE-15-1428Artikkel i tidsskrift (Fagfellevurdert)

A fully developed turbulent particle-gas flow in a rectangular horizontalchannel 100 × 10 × 4000 mm3 is disclosed with high spatial resolution2D Particle Image Velocimetry. The objective is to increase the knowledge ofthe mechanisms behind alterations in turbulent characteristics when adding twosets of relatively large solid spherical particles with mean diameters of 525and 755 μm and particle size distributions of 450 - 600 and 710 - 800 μm,respectively. Reynolds numbers are 4000 and 5600 and relatively high volumefraction of 5.4 × 10-4 and 8.0 × 10-4 are tested. Both thenear wall turbulent boundary layer flow and outer core flow are considered. Resultsshow that the carrier phase turbulent intensities increase with volume fractionof the inertial particles. The overall mean flowvelocity is affected when adding the particles but only to a minor extent. Nearthe wall, averaged velocity decreases while fluctuating velocity componentsincrease when particles are added to the flow. Quadrant analysis shows theimportance of sweep near the wall and ejection events in the region defined byy+ > 20. In conclusion, high inertia particles can enhanceturbulence even at relatively low Particle Reynolds number < 90. In the nearbottom wall region particles tend to be a source of instability reflected asenhancement in rms values of the normal velocity component.

• 31.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Turbulent modulation in particulate flow: A review of critical variables2015Inngår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 7, nr 10, s. 597-609, artikkel-id 8102444Artikkel i tidsskrift (Fagfellevurdert)

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

• 32.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Experimental study of the effect from bio-solid particles on fully developed turbulent duct flow2014Konferansepaper (Fagfellevurdert)
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• 33.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall Research and Development, Älvkarleby, Sweden. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall Research and Development, Älvkarleby, Sweden . Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Numerical modelling of flow in parallel spillways2020Inngår i: Proceedings of the 8th IAHR International Symposium on Hydraulic Structures ISHS2020, The University of Queensland , 2020Konferansepaper (Fagfellevurdert)

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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• 34.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Parallel computing of fluid flow through porous media2007Licentiatavhandling, med artikler (Annet vitenskapelig)

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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• 35.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
Simulation and experiments of entrance flow conditions to a fishway2016Konferansepaper (Fagfellevurdert)

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

• 36. Hellström, Gunnar
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Flow through porous media at moderate Reynolds number2006Inngår i: Proceedings, 4th International Scientific Colloquium Modelling for Material Processing, 2006, s. 129-134Konferansepaper (Fagfellevurdert)

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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• 37.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Parallel CFD simulations of an original and redesigned hydraulic turbine draft tube2007Inngår i: Advances in Engineering Software, ISSN 0965-9978, E-ISSN 1873-5339, Vol. 38, nr 5, s. 338-344Artikkel i tidsskrift (Fagfellevurdert)

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.

• 38.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Internal erosion in embankment dams: fluid flow through and deformation of porous media2009Doktoravhandling, med artikler (Annet vitenskapelig)

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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• 39.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Representative volume size when modelling flow through porous structures2014Konferansepaper (Fagfellevurdert)
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• 40.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
Mechanisms of flow-induced deformation of porous media2010Inngår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 664, s. 220-237Artikkel i tidsskrift (Fagfellevurdert)

The study investigates creeping flow-induced alteration in the permeability of deformable particle systems. Low-Reynolds-number transversal flow through random arrays of aligned cylinders is considered by means of a combined methodology of directly solving the two-dimensional (2D) Stokes equations for the flow in the vicinity of two particles and minimising the dissipation rate in a system comprising thousands of particles. The results demonstrate that the more compact the system, the greater the possible relative change of permeability when a high flow rate is applied. The permeability of large random arrays always increases when increasing the flow rate, which is most apparent in compact systems with equal-sized particles. The permeability can sometimes decrease but only in structured or small systems.

• 41.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Mechanisms of fluid flow induced deformation of porous medium2009Inngår i: Proceedings of 4th ICAPM: August 10-12, 2009, Istanbul, Turkey, 2009Konferansepaper (Fagfellevurdert)
• 42.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Mekanismer för flödesinducerad deformation av ett poröst material2009Inngår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 103-Konferansepaper (Annet vitenskapelig)
• 43.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Epsilon HighTech AB, Göteborg.
Laminar and turbulent flow through an array of cylinders2010Inngår i: Journal of Porous Media, ISSN 1091-028X, E-ISSN 1934-0508, Vol. 13, nr 12, s. 1073-1085Artikkel i tidsskrift (Fagfellevurdert)

When modeling fluid flow through porous media it is necessary to know when to take inertia effects into account, as well as when to switch to a turbulent description of the flow. From an engineering point of view, the problem is often solved with the empirically derived Ergun equation or a recently upgraded version by Nemec and Levec [Chem. Eng. Sci., vol. 60, pp. 6947−6957, 2005]. The drawback with this approach is, however, that the mechanisms for the transitions between the three states of flow are not revealed and time-consuming experiments have to be performed. In order to increase knowledge of the detailed flow, numerical studies of flow through arrays of quadratically packed cylinders at a variety of Re values were carried out. One result is that the laminar and turbulent approaches used both mimic experimental results for low Re, while for higher Re only the turbulent approach resembles the empirically derived equations. The deviation from Darcy’s law for different porosities of the array can be defined by usage of Re based on the hydraulic radius and the average interstitial velocity. However, to find a common Re when turbulence need to be accounted for, another Re based solely on the averaged interstitial velocity and the diameter of the cylinders was used. It was found that at low Re the laminar and turbulent setups give practically the same velocity fields, while the turbulent dissipation at higher Re results in larger circulation zones and weaker jets.

• 44. Hellström, J. Gunnar I.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Flow through a hexagonal array of perturbed spheres at low to high Reynolds number2007Inngår i: Abstracts of the Second International Conference on Porous Media and its Applications in Science, Engineering and Industry, Engineering Conferences International , 2007Konferansepaper (Fagfellevurdert)

When performing numerical simulations of fluid flow through porous media it is necessary to know when to switch from a creeping flow formulation to a more elaborate laminar description. In the creeping flow regime the Darcy law is sufficient while when inertia-effects become significant it is necessarily to use the full Navier-Stokes equations or at least add a non-linear term to Darcy's law as done in the empirically derived Ergun equation. The latter equation has also turned out to be valid for turbulent flows. It is however not obvious which equation to use at a certain Reynolds number. In order to solve this problem Computational Fluid Dynamics is used to derive the apparent permeability of a hexagonal packed array of spheres. In addition the forces acting on the spheres are derived when a perturbation in the form of a spherically shaped particle is introduced in the pore space. Then simulations are performed at various Reynolds number ranging from the creeping flow region to moderate Reynolds number flows. The simulations are carried out with the commercially available software, ANSYS CFX 11.0, with a particular effort on grid refinement and numerical iteration in order to secure that the errors are sufficiently small. One result is that inertia effects become important already at Reynolds number about 5 for as well the array as the perturbed geometry. As the particle radius increases the shear and normal forces per unit area decreases. In general, these forces increase with Reynolds number. The simulations however show that for some cases the normal forces per unit area decreases and even change sign as Reynolds number increases.

• 45.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Forces on grains located in model geometry with application to internal erosion in embankment dams2007Inngår i: International Symposium on Modern Technology of Dams: The 4th EADC Symposium, 2007, s. 375-386Konferansepaper (Fagfellevurdert)

For a comprehensive understanding of internal erosion in embankment dams it is necessary to elucidate the detailed seepage flow. A neat tool that can be used for this purpose is Computational Fluid Dynamics. With such a tool forces on individual particles can be derived and means to decide when to switch from a creeping flow formulation to a more elaborate laminar description for macroscopic flow simulations can be derived. It can even be decided when the transition from a laminar formulation to a fully turbulent description should take place. In the creeping flow regime a Darcy law formulation is sufficient while when inertia-effects become significant it is necessary to use the Navier-Stokes equations or at least add a non-linear term to Darcy's law as done in the empirically derived Ergun equation. It is, however, not obvious which equation to use at a certain Reynolds number. Hence, Computational Fluid Dynamics is here used to derive the apparent permeability of a hexagonal packed array of spheres. Then, grains are introduced in the pore space between the spheres and forces acting on the grains are derived. It will then be possible to decide at what conditions such particles will start to move, due to flow induced forces, and thereby initiating internal erosion. The simulations are performed at various Reynolds number ranging from the creeping flow region to the transition regime. The software ANSYS CFX 11.0 is applied with particular effort on grid refinement and numerical iteration in order to secure that the numerical errors are sufficiently small. One result is that inertia-effects become important already at a Reynolds number of 10. Another is that the forces acting on the grains can decrease as a function of Reynolds number and can as well be dependent on the geometry of the grains, even though the force per unit area on the array of spheres increases. Interestingly, the direction of the forces on the grains can even be opposite to the main flow direction.

• 46.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
CFD-simulations of fluid flow through an array of hexagonal or quadratic packed cylinders: laminar versus turbulent formulations2009Inngår i: Proceedings of 4th ICAPM: August 10-12, 2009, Istanbul, Turkey, 2009Konferansepaper (Fagfellevurdert)
• 47. Hellström, J. Gunnar I.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Flow induced forces in porous media with application to internal erosion2008Inngår i: Proceedings of the 19th International Symposium on Transport Phenomena (ISTP-19): Reykjavik, Iceland, August 17-21, 2008 / [ed] Sigurdur Brynjolfsson; Olafur Petur Palsson; Jong H Kim, University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science , 2008Konferansepaper (Fagfellevurdert)

For a comprehensive understanding of internal erosion in embankment dams it is necessary to elucidate the detailed seepage flow. A neat tool that can be used for this purpose is Computational Fluid Dynamics in which forces on individual particles in a porous media can be derived. The model geometry chosen to represent the porous media is a hexagonal array of spheres into which smaller particles are introduced which are supposed to move at a certain level of flow induced forces. It is shown that the mesh deformation method introduced has a potential to model internal erosion.

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• 48. Hellström, J. Gunnar I.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Flöde genom poröost material vid varierande Reynolds tal2007Inngår i: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, s. 63-Konferansepaper (Annet vitenskapelig)
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• 49. Hellström, J. Gunnar I.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Numerical simulations of fluid flow through model geometries of porous media: at low to high Reynolds number2008Inngår i: Heat Transfer, Fluid Mechanics & Thermodynamics, HEFAT 2008: Proceedings of the Sixth International Conference, Pretoria, South Africa, 30 June-2 July 2008, Pretoria: University of Pretoria, South Africa , 2008Konferansepaper (Fagfellevurdert)

When modeling fluid flow through porous media it is necessary to know when to switch from a creeping flow formulation to a more elaborate laminar description or to a fully turbulent one. This is of importance in a large number of industrial processes such as flow through embankment dams, composites manufacturing, filtering and in the refinement of iron ore pellets. Regarding the creeping flow regime the Darcy law is sufficient while when inertia-effects become significant it is necessary to use the full Navier-Stokes equations or at least add a non-linear term to Darcy's law as done in the empirically derived Ergun equation, which has also turned out to be valid for some turbulent flows. It is however not obvious which equation to use at a certain Reynolds number and on what velocities and length scales Reynolds number should be based on. In order to shed some light on this Computational Fluid Dynamics is here applied to simple model geometries of porous media. In particular the flow through quadratic and hexagonal arrays of cylinders is studied. The main quantities of interest are the apparent permeability, the Blake-type friction factor as well as the forces acting on the cylinders. The simulations are carried out for a wide range of Reynolds number ranging from the creeping region to rather high Reynolds number flow, considering flow in porous media. The simulations are based on as well a laminar flow formulation as a turbulent one where the turbulence model chosen is the Shear Stress Transport model, and the CFD-software used is ANSYS CFX with extra care regarding grid resolution and numerical iteration in order to secure that the numerical errors are sufficiently small. One result is that inertia-effects become significant already at Reynolds number of about 10, for the quadratic packing, but around 50 for the hexagonal arrangement and the region where the laminar simulations differ considerably from the turbulent calculations is dependent on the different array arrangements.

• 50.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
Fluid mechanics of internal erosion in embankment dams2007Inngår i: Parallel computing of fluid flow through porous media, Luleå: Luleå tekniska universitet, 2007Kapittel i bok, del av antologi (Annet vitenskapelig)
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