Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 314) Show all publications
Jouybari, N., Maerefat, M., Lundström, T. S., Eshagh Nimvari, M. & Gholami, Z. (2018). A General Macroscopic Model for Turbulent Flow in Porous Media. Journal of Fluids Engineering - Trancactions of The ASME, 140(1), Article ID 011201.
Open this publication in new window or tab >>A General Macroscopic Model for Turbulent Flow in Porous Media
Show others...
2018 (English)In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 140, no 1, article id 011201Article in journal (Refereed) Published
Abstract [en]

The present study deals with the generalization of a macroscopic turbulence model in porous media using a capillary model. The additional source terms associated with the production and dissipation of turbulent kinetic energy due to the presence of solid matrix are calculated using the capillary model. The present model does not require any prior pore scale simulation of turbulent flow in a specific porous geometry in order to close the macroscopic turbulence equations. Validation of the results in packed beds, periodic arrangement of square cylinders, synthetic foams and longitudinal flows such as pipes, channels and rod bundles against available data in the literature reveals the ability of the present model in predicting turbulent flow characteristics in different types of porous media. Transition to the fully turbulent regime in porous media and different approaches to treat this phenomenon are also discussed in the present study. Finally, the general model is modified so that it can be applied to lower Reynolds numbers below the range of fully turbulent regime in porous media.

Place, publisher, year, edition, pages
The American Society of Mechanical Engineers (ASME), 2018
National Category
Engineering and Technology Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-65199 (URN)10.1115/1.4037677 (DOI)000415379500009 ()2-s2.0-85029753712 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-10-03 (andbra)

Available from: 2017-08-19 Created: 2017-08-19 Last updated: 2018-11-27Bibliographically approved
Andersson, L. R., Larsson, S., Hellström, J. G., Andreasson, P., Andersson, A. G. & Lundström, S. (2018). Characterisation of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations. Engineering, 10, 399-416
Open this publication in new window or tab >>Characterisation of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations
Show others...
2018 (English)In: Engineering, ISSN 1947-3931, Vol. 10, p. 399-416Article in journal (Refereed) Published
Abstract [en]

High Reynolds number flow inside a channel of rectangular cross section is examined using Particle Image Velocimetry. One wall of the channel has been replaced with a surface of a roughness representative to that of real hydropower tunnels, i.e. a random terrain with roughness dimensions typically in the range of ≈10% - 20% of the channels hydraulic radius. The rest of the channel walls can be considered smooth. The rough surface was captured from an existing blasted rock tunnel using high resolution laser scanning and scaled to 1:10. For quantification of the size of the largest flow structures, integral length scales are derived from the auto-correlation functions of the temporally averaged velocity. Additionally, Proper Orthogonal Decomposition (POD) and higher-order statistics are applied to the instantaneous snapshots of the velocity fluctuations. The results show a high spatial heterogeneity of the velocity and other flow characteristics in vicinity of the rough surface, putting outer similarity treatment into jeopardy. Roughness effects are not confined to the vicinity of the rough surface but can be seen in the outer flow throughout the channel, indicating a different behavior than postulated by Townsend’s similarity hypothesis. The effects on the flow structures vary depending on the shape and size of the roughness elements leading to a high spatial dependence of the flow above the rough surface. Hence, any spatial averaging, e.g. assuming a characteristic sand grain roughness factor, for determining local flow parameters becomes less applicable in this case.

Place, publisher, year, edition, pages
Scientific Research Publishing, 2018
Keywords
CFD, Validation, Hydraulic Roughness, PIV, Hydropower
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-71097 (URN)10.4236/eng.2018.107028 (DOI)
Available from: 2018-10-04 Created: 2018-10-04 Last updated: 2018-10-08Bibliographically approved
Wibron, E., Ljung, A.-L. & Lundström, S. (2018). Computational Fluid Dynamics Modeling and Validating Experiments of Airflow in a Data Center. Energies, 11(3), Article ID 644.
Open this publication in new window or tab >>Computational Fluid Dynamics Modeling and Validating Experiments of Airflow in a Data Center
2018 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 3, article id 644Article in journal (Refereed) Published
Abstract [en]

The worldwide demand on data storage continues to increase and both the number and the size of data centers are expanding rapidly. Energy efficiency is an important factor to consider in data centers since the total energy consumption is huge. The servers must be cooled and the performance of the cooling system depends on the flow field of the air. Computational Fluid Dynamics (CFD) can provide detailed information about the airflow in both existing data centers and proposed data center configurations before they are built. However, the simulations must be carried out with quality and trust. The k–ɛ model is the most common choice to model the turbulent airflow in data centers. The aim of this study is to examine the performance of more advanced turbulence models, not previously investigated for CFD modeling of data centers. The considered turbulence models are the k–ɛ model, the Reynolds Stress Model (RSM) and Detached Eddy Simulations (DES). The commercial code ANSYS CFX 16.0 is used to perform the simulations and experimental values are used for validation. It is clarified that the flow field for the different turbulence models deviate at locations that are not in the close proximity of the main components in the data center. The k–ɛ model fails to predict low velocity regions. RSM and DES produce very similar results and, based on the solution times, it is recommended to use RSM to model the turbulent airflow data centers.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
data center; airflow; computational fluid dynamics (CFD); turbulence models
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-67958 (URN)10.3390/en11030644 (DOI)000428304300172 ()
Note

Validerad;2018;Nivå 2;2018-03-19 (andbra)

Available from: 2018-03-16 Created: 2018-03-16 Last updated: 2018-11-26Bibliographically approved
Altorkmany, L., Kharseh, M., Ljung, A.-L. & Lundström, S. (2018). Effect of Working Parameters of the Plate Heat Exchanger on the Thermal Performance of the Anti-Bact Heat Exchanger System to Disinfect Legionella in Hot Water Systems. Applied Thermal Engineering, 141, 435-443
Open this publication in new window or tab >>Effect of Working Parameters of the Plate Heat Exchanger on the Thermal Performance of the Anti-Bact Heat Exchanger System to Disinfect Legionella in Hot Water Systems
2018 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 141, p. 435-443Article in journal (Refereed) Published
Abstract [en]

The objective of the current study is to analyze the effect of different working parameters on the thermal performance of the Anti-Bact Heat Exchanger system (ABHE). The ABHE system is inspired by nature and implemented to achieve continuous disinfection of Legionella in different human-made water systems at any desired disinfection temperature. In the ABHE system, most of the energy is recovered using an efficient plate heat exchanger (PHE). A model by Engineering Equation Solver (EES) is set-up to figure out the effect of different working parameters on the thermal performance of the ABHE system. The study shows that higher supplied water temperature can enhance the regeneration ratio (RR), but it requires a large PHE area and pumping power (PP) which consequently increase the cost of the ABHE system. However, elevate temperature in use results in a reduced PHE area and PP, which accordingly reduce the cost of the ABHE system. On the other hand, the EES-based model is used to study the effect of the length and the width of the plates used in the PHE on the RR and the required area of the PHE. Finally, taking into account the geometrical parameters, flow arrangement and the initial operating conditions of the PHE, the EES-based model is used to optimize the PHE in which its area is minimized, and the RR of the ABHE system is maximized.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Legionella; thermal disinfection; simulation; thermal performance; plate heat exchanger
National Category
Engineering and Technology Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-67443 (URN)10.1016/j.applthermaleng.2018.06.002 (DOI)000440958800041 ()2-s2.0-85048500460 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-06-13 (andbra)

Available from: 2018-01-31 Created: 2018-01-31 Last updated: 2018-08-30Bibliographically approved
Karlsson, L., Ljung, A.-L. & Lundström, T. S. (2018). Modelling the dynamics of the flow within freezing water droplets. Heat and Mass Transfer, 54(12), 3761-3769
Open this publication in new window or tab >>Modelling the dynamics of the flow within freezing water droplets
2018 (English)In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 54, no 12, p. 3761-3769Article in journal (Refereed) Published
Abstract [en]

The flow within freezing water droplets is here numerically modelled assuming fixed shape throughout freezing. Three droplets are studied with equal volume but different contact angles and two cases are considered, one including internal natural convection and one where it is excluded, i.e. a case where the effects of density differences is not considered. The shape of the freezing front is similar to experimental observations in the literature and the freezing time is well predicted for colder substrate temperatures. The latter is found to be clearly dependent on the plate temperature and contact angle. Including density differences has only a minor influence on the freezing time, but it has a considerable effect on the dynamics of the internal flow. To exemplify, in the vicinity of the density maximum for water (4 C) the velocities are about 100 times higher when internal natural convection is considered for as compared to when it is not.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-69879 (URN)10.1007/s00231-018-2396-1 (DOI)2-s2.0-85049030106 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-12-04 (inah)

Available from: 2018-06-26 Created: 2018-06-26 Last updated: 2018-12-04Bibliographically approved
Sarkar, C., Westerberg, L.-G., Höglund, E. & Lundström, S. T. (2018). Numerical simulations of lubricating grease flow in a rectangular channel with and without restrictions. Tribology Transactions, 61(1), 144-156
Open this publication in new window or tab >>Numerical simulations of lubricating grease flow in a rectangular channel with and without restrictions
2018 (English)In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 61, no 1, p. 144-156Article in journal (Refereed) Published
Abstract [en]

This article presents numerical simulations of the laminar flow of lubricating greases in a channel with rectangular cross section. Three greases with different consistencies (NLGI grades 00, 1, and 2) have been considered in three different configurations composed of a rectangular channel without restrictions, one rectangular step restriction, and one double-lip restriction. The driving pressure drop over the channel spans from 30 to 250 kPa. The grease rheology is described by the Herschel-Bulkley rheology model, and both the numerical code and rheology model have been validated with analytical solutions and flow measurements using micro-particle image velocimetry.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Fluid Mechanics and Acoustics Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Fluid Mechanics; Machine Elements
Identifiers
urn:nbn:se:ltu:diva-61479 (URN)10.1080/10402004.2017.1285090 (DOI)000432222500015 ()
Note

Validerad;2018;Nivå 2;2018-02-01 (rokbeg)

Available from: 2017-01-17 Created: 2017-01-17 Last updated: 2018-06-04Bibliographically approved
Teng, Z., Larsson, S., Lundström, S. & Marjavaara, B. D. (2018). The Effect of Reynolds Number on Jet in Asymmetric Co-Flows: A CFD Study. International Journal of Chemical Engineering, Article ID 1572576.
Open this publication in new window or tab >>The Effect of Reynolds Number on Jet in Asymmetric Co-Flows: A CFD Study
2018 (English)In: International Journal of Chemical Engineering, ISSN 1687-806X, E-ISSN 1687-8078, article id 1572576Article in journal (Refereed) Published
Abstract [en]

In rotary kilns in grate-kiln systems for iron ore pelletizing, a long and stable jet flame is needed to ensure a high quality of the pellets. The primary jet issuing from the nozzle interacts with two asymmetric co-flows creating a very complex flow. In order to better understand and eventually model this flow with quality and trust, simplified cases need to be studied. In this work, a simplified and virtual model is built based on a down-scaled kiln model established in a previous experimental work. The aim is to numerically study the jet development as a function of position and Reynolds number (Re). The numerical simulations are carried out with the standard k-ε model, and quite accurate velocity profiles are obtained while the centerline decays and spreading of the passive scalars are over predicted. The model is capable of predicting a Re dependency of the jet development. With increasing Re, the jet is longer while it generally decays and spreads faster resulting from the stronger shear between the jet and co-flows and the stronger entrainment from the recirculation zone. This recirculation found in the simulations restrain the momentum spreading in the spanwise direction, leading to a slower velocity spreading with higher Re. For further validation and understanding, more measurements in the shear layer and simulations with more advanced turbulence models are necessary

Place, publisher, year, edition, pages
Hindawi Publishing Corporation, 2018
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-71461 (URN)10.1155/2018/1572576 (DOI)000449197900001 ()2-s2.0-85056223095 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-11-06 (johcin) 

Available from: 2018-11-06 Created: 2018-11-06 Last updated: 2018-12-05Bibliographically approved
Larsson, S., Lundström, S. & Lycksam, H. (2018). Tomographic PIV of flow through ordered thin porous media. Experiments in Fluids, 59(6), Article ID 96.
Open this publication in new window or tab >>Tomographic PIV of flow through ordered thin porous media
2018 (English)In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 59, no 6, article id 96Article in journal (Refereed) Published
Abstract [en]

Pressure-driven flow in a model of a thin porous medium is investigated using tomographic particle image velocimetry. The solid parts of the porous medium have the shape of vertical cylinders placed on equal interspatial distance from each other. The array of cylinders is confined between two parallel plates, meaning that the permeability is a function of the diameter and height of the cylinders, as well as their interspatial distance. Refractive index matching is applied to enable measurements without optical distortion and a dummy cell is used for the calibration of the measurements. The results reveal that the averaged flow field changes substantially as Reynolds number increases, and that the wakes formed downstream the cylinders contain complex, three-dimensional vortex structures hard to visualize with only planar measurements. An interesting observation is that the time-averaged velocity maximum changes position as Reynolds number increases. For low Reynolds number flow, the maximum is in the middle of the channel, while, for the higher Reynolds numbers investigated, two maxima appear closer to each bounding lower and upper wall.

Place, publisher, year, edition, pages
Springer, 2018
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-68773 (URN)10.1007/s00348-018-2548-6 (DOI)2-s2.0-85047216388 (Scopus ID)
Note

Validerad;2018;Nivå 1;20180525 (marisr)

Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2018-11-15Bibliographically approved
Xie, Q., Yang, J., Lundström, S. & Dai, W. (2018). Understanding morphodynamic changes of a tidal river confluence through field measurements and numerical modeling. Water, 10(10), Article ID 1424.
Open this publication in new window or tab >>Understanding morphodynamic changes of a tidal river confluence through field measurements and numerical modeling
2018 (English)In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 10, no 10, article id 1424Article in journal (Refereed) Published
Abstract [en]

A confluence is a natural component in river and channel networks. This study deals, through field and numerical studies, with alluvial behaviors of a confluence affected by both river run-offand strong tides. Field measurements were conducted along the rivers including the confluence. Field data show that the changes in flow velocity and sediment concentration are not always in phase with each other. The concentration shows a general trend of decrease from the river mouth to the confluence. For a given location, the tides affect both the sediment concentration and transport. A two-dimensional hydrodynamic model of suspended load was set up to illustrate the combined effects of run-offand tidal flows. Modeled cases included the flood and ebb tides in a wet season. Typical features examined included tidal flow fields, bed shear stress, and scour evolution in the confluence. The confluence migration pattern of scour is dependent on the interaction between the river currents and tidal flows. The flood tides are attributable to the suspended load deposition in the confluence, while the ebb tides in combination with run-offs lead to erosion. The flood tides play a dominant role in the morphodynamic changes of the confluence. 

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
tidal river confluence, flow features, morphological changes, field measurements, numerical simulations
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-71350 (URN)10.3390/w10101424 (DOI)2-s2.0-85054725343 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-10-26 (svasva)

Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2018-10-26Bibliographically approved
Burström, P., Frishfelds, V., Ljung, A.-L., Lundström, T. S. & Marjavaara, D. (2017). Discrete and continuous modelling of convective heat transport in a thin porous layer of mono sized spheres (ed.). Heat and Mass Transfer, 53(1), 151-160
Open this publication in new window or tab >>Discrete and continuous modelling of convective heat transport in a thin porous layer of mono sized spheres
Show others...
2017 (English)In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 53, no 1, p. 151-160Article in journal (Refereed) Published
Abstract [en]

Convective heat transport in a relatively thin porous layer of monosized particles is here modeled. The size of the particles is only one order of magnitude smaller than the thickness of the layer. Both a discrete three-dimensional system of particles and a continuous one-dimensional model are considered. The methodology applied for the discrete system is Voronoi discretization with minimization of dissipation rate of energy. The discrete and continuous model compares well for low velocities for the studied uniform inlet boundary conditions. When increasing the speed or for a thin porous layer however, the continuous model diverge from the discrete approach if a constant dispersion is used in the continuous approach. The new result is thus that a special correlation must be used when using a continuous model for flow perpendicular to a thin porous media in order to predict the dispersion in proper manner, especially in combination with higher velocities.

Place, publisher, year, edition, pages
Springer, 2017
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-9656 (URN)10.1007/s00231-016-1792-7 (DOI)000391384700014 ()2-s2.0-84962175661 (Scopus ID)85295f62-d81d-468a-a26b-53cc1547fcd2 (Local ID)85295f62-d81d-468a-a26b-53cc1547fcd2 (Archive number)85295f62-d81d-468a-a26b-53cc1547fcd2 (OAI)
Note

Validerad; 2017; Nivå 2; 2017-03-15 (inah)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-09-27Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1033-0244

Search in DiVA

Show all publications