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  • 1.
    Hamedi, Naser
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    On the Interaction of Side-By-Side Circular Cylinders in Viscoplastic Fluids2019Inngår i: Fluids, E-ISSN 2311-5521, Vol. 4, nr 2, artikkel-id 93Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, the static interaction of a train of three cylinders in a Bingham fluid is studiednumerically using Computational Fluid Dynamics. The variation of drag forces for the cylinders inseveral configurations is investigated. Positions of the particles in relation to the reference particleare recognized by the separation distance between the cylinders. A steady state field is considered,with Bingham numbers between 5 and 150. Several separation distances (d) were considered, such that2.0D d 6.0D where D is the cylinder diameter. The Reynolds number was chosen in the range of5 Re 40. In particular, the eect of the separation distance, Reynolds number and Bingham numberon the shape and size of the unyielded regions was investigated. The functional dependence of thisregion and the drag coecient is explored. The present results reveal the significant influence of thegap between the cylinders on the drag force and the shape of the unyielded regions surrounding thecylinders. It was found that there are several configurations in which the drag forces over the first andthe third cylinders are almost equal depending on variation of the Bi, Re and the separation distance.

  • 2.
    Larsson, I.A Sofia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    The Aerodynamics of an Iron Ore Pelletizing Rotary Kiln2022Inngår i: Fluids, E-ISSN 2311-5521, Vol. 7, nr 5, artikkel-id 160Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper summarizes more than a decade of systematic studies of the flow field in an iron ore pelletizing rotary kiln using computational fluid dynamics (CFD) on simplified models of a real kiln. Physical, laser-based experiments have been performed to validate part of the numerical results. The objective is a better understanding of the kiln aerodynamics and, by extension, its effect on the combustion process. Despite all of the simplifications regarding the models studied in this project, the results show the importance of correctly predicting the flow field in order to optimize the combustion process. Combustion simulations revealed that the heat release from the flame does not affect or change the flow field in any significant way; the flow field, however, governs the flame propagation and affects the combustion process by controlling the mixing rates of fuel and air. Using down-scaled isothermal water models for investigating kiln aerodynamics in general and mixing properties in particular is therefore justified. Although the heat release from the flame cannot be accounted for in isothermal models, valuable implications regarding the real process can still be gained. To better model the actual process numerically, more advanced submodels for both the combustion and especially the flow field are needed. The complex flow field in this type of rotary kiln requires a careful choice of turbulence model to obtain accurate simulation results.

  • 3.
    Shankar, Vijay
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Lundberg, Anton
    VOLVO AB, Gropegårdsgatan 2, 417 15 Göteborg, Sweden.
    Pamidi, Taraka
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Landström, Lars-Olof
    ÅF Industry AB, Grafiska vägen 2, 401 51 Göteborg, Sweden.
    Johansson, Örjan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    CFD Analysis of Turbulent Fibre Suspension Flow2020Inngår i: Fluids, E-ISSN 2311-5521, Vol. 5, nr 4, artikkel-id 175Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new model for turbulent fibre suspension flow is proposed by introducing a model for the fibre orientation distribution function (ODF). The coupling between suspended fibres and the fluid momentum is then introduced through the second and fourth order fibre orientation tensors, respectively. From the modelled ODF, a method to construct explicit expressions for the components of the orientation tensors as functions of the flow field is derived. The implementation of the method provides a fibre model that includes the anisotropic detail of the stresses introduced due to presence of the fibres, while being significantly cheaper than solving the transport of the ODF and computing the orientation tensors from numerical integration in each iteration. The model was validated and trimmed using experimental data from flow over a backwards facing step. The model was then further validated with experimental data from a turbulent fibre suspension channel flow. Simulations were also carried out using a Bingham viscoplastic fluid model for comparison. The ODF model and the Bingham model performed reasonably well for the turbulent flow areas, and the latter model showed to be slightly better given the parameter settings tested in the present study. The ODF model may have good potential, but more rigorous study is needed to fully evaluate the model.

  • 4.
    Xie, Qiancheng
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Yang, James
    Vattenfall AB, Älvkarleby; Royal Institute of Technology, Stockholm, Sweden.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Field Studies and 3D Modelling of Morphodynamics in a Meandering River Reach Dominated by Tides and Suspended Load2019Inngår i: Fluids, E-ISSN 2311-5521, Vol. 4, nr 1, artikkel-id 15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Meandering is a common feature in natural alluvial streams. This study deals with alluvial behaviors of a meander reach subjected to both fresh-water flow and strong tides from the coast. Field measurements are carried out to obtain flow and sediment data. Approximately 95% of the sediment in the river is suspended load of silt and clay. The results indicate that, due to the tidal currents, the flow velocity and sediment concentration are always out of phase with each other. The cross-sectional asymmetry and bi-directional flow result in higher sediment concentration along inner banks than along outer banks of the main stream. For a given location, the near-bed concentration is 2−5 times the surface value. Based on Froude number, a sediment carrying capacity formula is derived for the flood and ebb tides. The tidal flow stirs the sediment and modifies its concentration and transport. A 3D hydrodynamic model of flow and suspended sediment transport is established to compute the flow patterns and morphology changes. Cross-sectional currents, bed shear stress and erosion-deposition patterns are discussed. The flow in cross-section exhibits significant stratification and even an opposite flow direction during the tidal rise and fall; the vertical velocity profile deviates from the logarithmic distribution. During the flow reversal between flood and ebb tides, sediment deposits, which is affected by slack-water durations. The bed deformation is dependent on the meander asymmetry and the interaction between the fresh water flow and tides. The flood tides are attributable to the deposition, while the ebb tides, together with run-offs, lead to slight erosion. The flood tides play a key role in the morphodynamic changes of the meander reach.

    Fulltekst (pdf)
    fulltext
  • 5.
    Yang, James
    et al.
    Vattenfall AB, Research & Development (R & D), Hydraulic Laboratory, Älvkarleby, Sweden;Division of Resources, Energy & Infrastructure, Royal Institute of Technology, Stockholm, Sweden.
    Andreasson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik. Vattenfall AB, Research & Development (R & D), Hydraulic Laboratory, Älvkarleby, Sweden.
    Teng, Penghua
    Division of Resources, Energy & Infrastructure, Royal Institute of Technology, Stockholm, Sweden.
    Xie, Qiancheng
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    The Past and Present of Discharge Capacity Modeling for Spillways: A Swedish Perspective2019Inngår i: Fluids, E-ISSN 2311-5521, Vol. 4, nr 10, artikkel-id 4010010Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most of the hydropower dams in Sweden were built before 1980. The present dam-safety guidelines have resulted in higher design floods than their spillway discharge capacity and the need for structural upgrades. This has led to renewed laboratory model tests. For some dams, even computational fluid dynamics (CFD) simulations are performed. This provides the possibility to compare the spillway discharge data between the model tests performed a few decades apart. The paper presents the hydropower development, the needs for the ongoing dam rehabilitations and the history of physical hydraulic modeling in Sweden. More than 20 spillways, both surface and bottom types, are analyzed to evaluate their discharge modeling accuracy. The past and present model tests are compared with each other and with the CFD results if available. Discrepancies do exist in the discharges between the model tests made a few decades apart. The differences fall within the range −8.3%–+11.2%. The reasons for the discrepancies are sought from several aspects. The primary source of the errors is seemingly the model construction quality and flow measurement method. The machine milling technique and 3D printing reduce the source of construction errors and improve the model quality. Results of the CFD simulations differ, at the maximum, by 3.8% from the physical tests. They are conducted without knowledge of the physical model results in advance. Following the best practice guidelines, CFD should generate results of decent accuracy for discharge prediction.

    Fulltekst (pdf)
    fulltext
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