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Hellström, J. Gunnar I.ORCID iD iconorcid.org/0000-0002-8360-9051
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Publications (10 of 92) Show all publications
Ghasemi Monfared, Z., Hellström, J. G. & Umeki, K. (2024). The Impact of Discrete Element Method Parameters on Realistic Representation of Spherical Particles in a Packed Bed. Processes, 12(1), Article ID 183.
Open this publication in new window or tab >>The Impact of Discrete Element Method Parameters on Realistic Representation of Spherical Particles in a Packed Bed
2024 (English)In: Processes, E-ISSN 2227-9717, Vol. 12, no 1, article id 183Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
MDPI, 2024
Keywords
packed bed, discrete element method, rolling friction, void fraction, sub-steps, wall effect
National Category
Fluid Mechanics and Acoustics Energy Engineering
Research subject
Energy Engineering; Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-103794 (URN)10.3390/pr12010183 (DOI)
Funder
Swedish Energy Agency, P46974-1
Note

Validerad;2024;Nivå 2;2024-01-17 (joosat);

Full text: CC BY 4.0 License

Available from: 2024-01-17 Created: 2024-01-17 Last updated: 2024-01-17Bibliographically approved
Sjöstedt, L. M., Hellström, J. G. & Andersson, A. G. (2023). CFD Modelling as a Tool to Better Understand Fish Behavior. In: Helmut Habersack; Michael Tritthart; Lisa Waldenberger (Ed.), Proceedings of the 40th IAHR World Congress - 2023: Rivers - Connecting Mountains and Coasts. Paper presented at 40th IAHR World Congress, Vienna , Austria, August 21-25, 2023 (pp. 2665-2672). International Association for Hydro-Environment Engineering and Research (IAHR)
Open this publication in new window or tab >>CFD Modelling as a Tool to Better Understand Fish Behavior
2023 (English)In: 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. 2665-2672Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
International Association for Hydro-Environment Engineering and Research (IAHR), 2023
National Category
Fluid Mechanics and Acoustics Ecology
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-103389 (URN)10.3850/978-90-833476-1-5_iahr40wc-p0582-cd (DOI)
Conference
40th IAHR World Congress, Vienna , Austria, August 21-25, 2023
Projects
Sustainable Hydropower
Funder
Swedish Energy Agency
Note

ISBN for host publication: 978-90-833476-1-5

Available from: 2023-12-21 Created: 2023-12-21 Last updated: 2023-12-21Bibliographically approved
Hedberg, P. A., Hellström, J. G. & Solheim, N. (2023). Experimental and computational evaluation of fish passageway with porous media boundary. In: Helmut Habersack; Michael Tritthart; Lisa Waldenberger (Ed.), Proceedings of the 40th IAHR World Congress - 2023: Rivers - Connecting Mountains and Coasts. Paper presented at 40th IAHR World Congress, Vienna , Austria, August 21-25, 2023 (pp. 2422-2428). International Association for Hydro-Environment Engineering and Research (IAHR)
Open this publication in new window or tab >>Experimental and computational evaluation of fish passageway with porous media boundary
2023 (English)In: 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, Published paper (Refereed)
Place, publisher, year, edition, pages
International Association for Hydro-Environment Engineering and Research (IAHR), 2023
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-98511 (URN)10.3850/978-90-833476-1-5_iahr40wc-p0908-cd (DOI)
Conference
40th IAHR World Congress, Vienna , Austria, August 21-25, 2023
Projects
Swedish Hydropower Centre / SVCSustainable Hydropower
Funder
Swedish Energy AgencyEnergy ResearchSwedish National GridLuleå University of TechnologyChalmers University of TechnologyKTH Royal Institute of TechnologyUppsala University
Note

ISBN for host publication: 978-90-833476-1-5

Available from: 2023-06-16 Created: 2023-06-16 Last updated: 2023-12-21Bibliographically approved
Burman, A. J., Andersson, A. G. & Hellström, J. G. (2023). Hydraulic classification of hydropeaking stages in a river reach. Rivers Research and Applications: an international journal devoted to river research and management, 39(4), 692-702
Open this publication in new window or tab >>Hydraulic classification of hydropeaking stages in a river reach
2023 (English)In: 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) Published
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.

Place, publisher, year, edition, pages
John Wiley & Sons, 2023
Keywords
delft3d, Fourier analysis, hydraulic stage, hydropeaking, hydropeaking frequency
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-94340 (URN)10.1002/rra.4098 (DOI)000907519300001 ()2-s2.0-85145677139 (Scopus ID)
Funder
EU, Horizon 2020, 764011
Note

Validerad;2023;Nivå 2;2023-07-21 (sofila);

This article has previously appeared as a manuscript in a thesis.

Available from: 2022-11-29 Created: 2022-11-29 Last updated: 2023-07-21Bibliographically approved
Höller, J. B., Andersson, A. G. & Hellström, J. G. (2023). Integrating Downstream Ecological, Social and Economic Effects of Hydropower to Hydraulic Modeling: A Review. World Journal of Mechanics, 13(8), 149-172
Open this publication in new window or tab >>Integrating Downstream Ecological, Social and Economic Effects of Hydropower to Hydraulic Modeling: A Review
2023 (English)In: World Journal of Mechanics, ISSN 2160-049X, E-ISSN 2160-0503, Vol. 13, no 8, p. 149-172Article, review/survey (Refereed) Published
Abstract [en]

Hydropower gains increasing importance as a steerable and controllable power source in a renewable energy mix and deregulated markets. Although hydropower produces fossil-free energy, it has a significant impact on the local environment. This review investigates the effects of flow alterations by hydropower on the downstream river system and the possibilities to integrate these effects into hydraulic modeling. The results show that various effects of flow regulation on the ecosystem, but also social and economic effects on related communities were observed in the last decades. The application of hydraulic models for investigations of ecological effects is common. Especially hydraulic effects and effects on fish were extensively modeled with the help of hydraulic 1D- and 2D-simulations. Current applications to investigate social and economic effects integrated into hydraulic modeling are meanwhile limited. Approaches to realizing this integration are presented. Further research on the economic valuation of ecosystems and integration of social and economic effects to hydraulic models is necessary to develop holistic tools to support decision-making on sustainable hydropower.

Keywords
Sustainable Hydropower, Hydraulic Simulation, River Regulation, Down-stream Effects, Integrated Modeling
National Category
Economics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-103481 (URN)10.4236/wjm.2023.138009 (DOI)
Note

Godkänd;2024;Nivå 0;2024-01-05 (hanlid);

Full text license: CC BY

Available from: 2024-01-05 Created: 2024-01-05 Last updated: 2024-01-05Bibliographically approved
Teng, P., Johansson, F. & Hellström, J. G. (2023). Modelling erosion of a single rock block using a coupled CFD-DEM approach. Journal of Rock Mechanics and Geotechnical Engineering, 15(9), 2375-2387
Open this publication in new window or tab >>Modelling erosion of a single rock block using a coupled CFD-DEM approach
2023 (English)In: Journal of Rock Mechanics and Geotechnical Engineering, ISSN 1674-7755, Vol. 15, no 9, p. 2375-2387Article in journal (Refereed) Published
Abstract [en]

Rock block removal is the prevalent physical mechanism for rock erosion and could affect the stability of dam foundations and spillways. Despite this, understanding of block removal is still inadequate because of the complex interactions among block characteristics, hydraulic forces, and erosive processes acting on the block. Herein, based on a previously conducted physical experiment of erosion of a single rock block, the removal processes of two different protruding blocks are represented by a coupled computational fluid dynamics-discrete element model (CFD-DEM) approach under varied flow conditions. Additionally, the blocks could be rotated with respect to the flow direction to consider the effect of the discontinuity orientation on the block removal process. Simulation results visualize the entire block removal process. The simulations reproduce the effects of the discontinuity orientation on the critical flow velocity inducing block incipient motion and the trajectory of the block motion observed in the physical experiments. The numerical results present a similar tendency of the critical velocities at different discontinuity orientations but have slightly lower values. The trajectory of the block in the simulations fits well with the experimental measurements. The relationship between the dimensionless critical shear stress and discontinuity orientation observed from the simulations shows that the effect of block protrusion becomes more dominant on the block incipient motion with the increase of relative protrusion height. To our knowledge, this present study is the first attempt to use the coupled finite volume method (FVM)-DEM approach for modelling the interaction behavior between the block and the flowing water so that the block removal process can be reproduced and analyzed.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Rock erosion, Block removal, Incipient motion, Coupled CFD-DEM, Critical shear stress
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-99600 (URN)10.1016/j.jrmge.2023.06.001 (DOI)2-s2.0-85164369936 (Scopus ID)
Note

Validerad;2023;Nivå 2;2023-11-07 (joosat);

Full text license: CC BY

Funder: Swedish Hydropower Centre

Available from: 2023-08-14 Created: 2023-08-14 Last updated: 2023-11-09Bibliographically approved
Teng, P., Hellström, J. G., Johansson, F. & Nilsson, C.-O. (2023). Modelling of erosion in rock spillway channels. In: : . Paper presented at Canadian Dam Association (CDA) 2023 Annual Conference & Trade Show, Winnipeg, Manitoba, Canada, October 22-25, 2023. Canadian Dam Association (CDA)
Open this publication in new window or tab >>Modelling of erosion in rock spillway channels
2023 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Erosion of rock channels downstream spillways may cause the significant deterioration of the spillways, raisingconcern for the safety of the dam. To evaluate the occurrence of rock erosion, this paper aims to employ a resolvedComputational Fluid Dynamics (CFD)-Discrete Element Method (DEM) approach to model the erosion process of asingle rock block and to investigate the effects of different parameters. The approach models the interaction behaviorsbetween flowing water and rock blocks. Simulation results visualize the erosion process of the rock block, whichprovides a reference to determine the threshold of the initiation of rock erosion. The results show that the incipientmotion of the rock block is significantly affected by the joint aperture. With the increase of the joint aperture size, thepressure distribution on the block surface is altered. Simulation results of the rough channel model are compared witha smooth model, which points out the influence of channel roughness on the rock erosion process.

Abstract [fr]

Lérosion des canaux rocheux en aval des déversoirs peut entraîner une détérioration importante des déversoirs, ce quisoulève des inquiétudes quant à la sécurité du barrage. Pour évaluer simplement loccurrence de lérosion rocheuse, cetarticle vise à utiliser une approche résolue de la dynamique des fluides computationnelle (CFD)-méthode des élémentsdiscrets (DEM) pour modéliser le processus dérosion dun seul bloc de roche et pour étudier les effets de différentsparamètres. Lapproche modélise les comportements dinteraction entre leau courante et les blocs rocheux. Les résultatsde la simulation visualisent le processus dérosion du bloc rocheux, ce qui fournit une référence pour déterminer leseuil de l’initiation de lérosion . Les résultats montrent que le mouvement initial du bloc rocheux est significativementaffecté par louverture du joint. Avec laugmentation de la taille de louverture du joint, la répartition de la pression surla surface du bloc est modifiée. Les résultats de simulation du modèle de canal rugueux sont comparés à un modèlelisse, ce qui souligne linfluence significative de la rugosité du canal sur le processus dérosion de la roche

Place, publisher, year, edition, pages
Canadian Dam Association (CDA), 2023
Keywords
Spillway, Dam Safety, Rock Erosion, CFDEM
National Category
Geotechnical Engineering Other Civil Engineering
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-102359 (URN)
Conference
Canadian Dam Association (CDA) 2023 Annual Conference & Trade Show, Winnipeg, Manitoba, Canada, October 22-25, 2023
Available from: 2023-11-09 Created: 2023-11-09 Last updated: 2024-01-12Bibliographically approved
Forslund, T. O. .., Larsson, I. A., Hellström, J. G. & Lundström, T. S. (2023). Steady-State Transitions in Ordered Porous Media. Transport in Porous Media, 149(2), 551-577
Open this publication in new window or tab >>Steady-State Transitions in Ordered Porous Media
2023 (English)In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 149, no 2, p. 551-577Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer Nature, 2023
Keywords
FDM, Pore scale, Ordered porous media, Inertial transition
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-93182 (URN)10.1007/s11242-023-01966-w (DOI)001008440200001 ()2-s2.0-85161891565 (Scopus ID)
Funder
Swedish Research Council, 2017-04390
Note

Validerad;2023;Nivå 2;2023-08-15 (hanlid);

This article has previously appeared as a manuscript in a thesis.

Licens fulltext: CC BY License

Available from: 2022-09-22 Created: 2022-09-22 Last updated: 2023-09-05Bibliographically approved
Forslund, T. O. M., Larsson, I. A., Hellström, J. G. & Lundström, T. S. (2022). A dual-lattice hydrodynamic-thermal MRT-LBM model implemented on GPU for DNS calculations of turbulent thermal flows. International journal of numerical methods for heat & fluid flow, 35(5), 1703-1725
Open this publication in new window or tab >>A dual-lattice hydrodynamic-thermal MRT-LBM model implemented on GPU for DNS calculations of turbulent thermal flows
2022 (English)In: 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) Published
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.

Place, publisher, year, edition, pages
Emerald Group Publishing Limited, 2022
Keywords
Lattice Boltzmann method, Turbulence, Thermal flows, Direct numerical simulation
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-93178 (URN)10.1108/HFF-06-2022-0339 (DOI)000893826100001 ()2-s2.0-85143219027 (Scopus ID)
Funder
Swedish Research Council, 2017-04390
Note

Validerad;2023;Nivå 2;2023-07-13 (sofila);

This article has previously appeared as a manuscript in a thesis

Available from: 2022-09-22 Created: 2022-09-22 Last updated: 2023-10-14Bibliographically approved
Burman, A., Andersson, A. G., Hellström, J. G. & Xie, Q. (2022). Ecohydraulical Applications and Limitations of Calibrated Numerical 2D Models. In: Miguel Ortega-Sánchez (Ed.), Proceedings of the 39th IAHR World Congress: From Snow To Sea: . Paper presented at 39th IAHR World Congress, Granada, Spain, June 19-24, 2022 (pp. 1557-1564). International Association for Hydro-Environment Engineering and Research (IAHR)
Open this publication in new window or tab >>Ecohydraulical Applications and Limitations of Calibrated Numerical 2D Models
2022 (English)In: 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, Published paper (Refereed)
Place, publisher, year, edition, pages
International Association for Hydro-Environment Engineering and Research (IAHR), 2022
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-94339 (URN)10.3850/IAHR-39WC2521711920221796 (DOI)2-s2.0-85176466987 (Scopus ID)
Conference
39th IAHR World Congress, Granada, Spain, June 19-24, 2022
Funder
EU, Horizon 2020, 764011
Note

ISBN for host publication: 978-90-832612-1-8

Available from: 2022-11-29 Created: 2022-11-29 Last updated: 2023-12-20Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-8360-9051

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