Change search
Refine search result
34567 251 - 300 of 327
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 251. Marjavaara, Daniel
    et al.
    Ebermark, Sofia
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Compression moulding simulations of SMC using a multi-objective surrogate-based inverse modeling approach2009In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 45, no 5, p. 503-515Article in journal (Refereed)
    Abstract [en]

    A multiobjective surrogate-based inverse modeling technique to predict the spatial and temporal pressure distribution numerically during the fabrication of sheet moulding compounds (SMCs) is introduced. Specifically, an isotropic temperature-dependent Newtonian viscosity model of a SMC charge is fitted to experimental measurements via numerical simulations in order to mimic the temporal pressure distribution at two spatial locations simultaneously. The simulations are performed by using the commercial computational fluid dynamics (CFD) code ANSYS CFX-10.0, and the multiobjective surrogate-based fitting procedure proposed is carried out with a hybrid formulation of the NSGA-IIa evolutionary algorithm and the response surface methodology in Matlab. The outcome of the analysis shows the ability of the optimization framework to efficiently reduce the total computational load of the problem. Furthermore, the viscosity model assumed seems to be able to re solve the temporal pressure distribution and the advancing flow front accurately, which can not be said of the spatial pressure distribution. Hence, it is recommended to improve the CFD model proposed in order to better capture the true behaviour of the mould flow.

  • 252. Marjavaara, Daniel
    et al.
    Ebermark, Sofia
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Simulation of Compression moulding of SMC by using a multi-objective surrogate-based inverse modelling approach2008In: Proceedings of the XV International Conference on Mechanics of Composites Material, MCM-2008, 2008Conference paper (Other academic)
  • 253. Marjavaara, Daniel
    et al.
    Kamakoti, R.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Thakur, S.
    Wright, J.
    Shyy, W.
    Steady and unsteady CFD simulations of the Turbine-99 Draft Tube using CFX-5 and STREAM2005In: Turbine-99 III: Proceedings of the third IAHR/ERCOFTAC workshop on draft tube flow, Luleå: Luleå tekniska universitet, 2005, p. 83-99Conference paper (Refereed)
    Abstract [en]

    The numerical prediction of the flow field in a hydraulic turbine draft tube is very challenging due to its complex flow properties and has already been studied in detail in two former ERCOFTAC Turbine-99 workshops. In this third workshop yet another step to determine the state of the art techniques in draft tube flow simulation are taken. Three cases were suggested in the workshop, wherein we have contributed to the first two cases (Case 1 respectively Case 2) in this paper using the CFD codes CFX-5 and Loci-STREAM. For the first case (steady calculation), the turbulence is modeled with the standard k-ε model and Menter's BSL and SST k-ω models, whereas for the second case (unsteady calculation), we use the SST based DES turbulence model. Results from these simulations show that both codes predict about the same main flow structures although significant differences in detailed flow fields are noticed between the two codes and between applied turbulence models.

  • 254. Marjavaara, Daniel
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Automatic shape optimisation of a hydropower draft tube2003In: Proceedings of 4th ASME-JSME Joint Fluids Engineering Conference, American Society of Mechanical Engineers , 2003, Vol. Vol. 2, p. 1819-1824Conference paper (Refereed)
    Abstract [en]

    Draft tube designs have to a large extend been based on intuition and on the experience of the design engineer. In a close future, CFD simulations coupled with optimisation algorithms will assist in the search for an optimal technical solution. Such a shape optimisation technique to redesign an existing draft tube is presented in this paper. By this method, a design can be predicted in terms of a predefined objective function, here the pressure recovery factor. The optimisation is performed with the Response Surface Method (RSM) implemented on the commercial code iSIGHT7.0, while the CFD simulations are carried out with the commercial code CFX4.4. The boundary conditions are based on detailed experimental data and the turbulence is modelled with the standard k-ε turbulence model. With this set-up and with two different parameterisations, Adapted and Profile Design respectively, an optimal geometry of the ERCOFTAC Turbine-99 draft tube can be predicted.

  • 255. Marjavaara, Daniel
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Redesign of a sharp heel draft tube by a validated CFD-optimization2006In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 50, no 8, p. 911-924Article in journal (Refereed)
    Abstract [en]

    Numerical optimization techniques in flow design are often used to find optimal shape solutions, regarding, for instance, performance, flow behaviour, construction considerations and economical aspects. The present paper investigates the possibilities of using these techniques in the design process of a hydropower plant. This is realized by optimizing the shape of an existing sharp heel draft tube and validating the result with previously performed experiments. The actual shape optimization is carried out with the response surface methodology, by maximizing the average pressure recovery factor and minimizing the energy loss factor. The result from the optimization shows that it is possible to find an optimal solution on rather coarse grids. The location of the optimum is similar to the experiments, but the improvements are unexpectedly small. This surprising result indicates that the simulated flow field does not completely act as the real flow, which may be a result of the applied inlet boundary conditions, insufficient turbulence models and/or the steady flow assumption.

  • 256. Marjavaara, Daniel
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Response surface-based shape optimization of a Francis draft tube2007In: International journal of numerical methods for heat & fluid flow, ISSN 0961-5539, E-ISSN 1758-6585, Vol. 17, no 1, p. 34-45Article in journal (Refereed)
    Abstract [en]

    Purpose - This paper aims to develop an efficient and accurate numerical method that can be used in the design process of the waterways in a hydropower plant. Design/methodology/approach - A range of recently published (2002-2006) works, which aim to form the basis of a shape optimization tool for flow design and to increase the knowledge within the field of computational fluid dynamics (CFD) and surrogate-based optimization techniques. Findings - Provides information about how crude the optimization method can be regarding, for example, the design variables, the numerical noise and the multi objectives, etc. Research limitations/implications - It does not give a detailed interpretation of the flow behaviour due to the lack of validation data. Practical implications - A very useful flow design methodology that can be used in both academy and industry. Originality/value - Shape optimization of hydraulic turbine draft tubes with aid of CFD and numerical optimization techniques has not been performed until recently due to the high CPU requirements on CFD simulations. The paper investigates the possibilities of using the global optimization algorithm response surface methodology in the design process of a full scale hydraulic turbine draft tube.

  • 257. Marjavaara, Daniel
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Shape optimisation of a hydropower draft tube2004In: 22nd IAHR Symposium on Hydraulic Machinery and Systems: Stockholm, Sweden, June 29 - July 2, 2004, Stockholm: IAHR , 2004, Vol. A, p. A03.2.1-A03.2.11Conference paper (Refereed)
  • 258. Marjavaara, Daniel
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Simulation driven design applied to draft tubes using surrogate models2006In: 23rd IAHR Symposium on Hydraulic Machinery and Systems: Yokohama, Japan, October 17 - 21, 2006 ; [conference proceedings], 2006Conference paper (Refereed)
  • 259. Marjavaara, Daniel
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Goel, Tushar
    Department of Mechanical and Aerospace Engineering, University of Florida.
    Mack, Yolanda
    Department of Mechanical and Aerospace Engineering, University of Florida.
    Shyy, Wei
    Department of Aerospace Engineering, University of Michigan.
    Hydraulic turbine diffuser shape optimization by multiple surrogate model approximations of pareto fronts2007In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 129, no 9, p. 1228-1240Article in journal (Refereed)
    Abstract [en]

    A multiple surrogate-based optimization strategy in conjunction with an evolutionary algorithm has been employed to optimize the shape of a simplified hydraulic turbine diffuser utilizing three-dimensional Reynolds-averaged Navier-Stokes computational fluid dynamics solutions. Specifically, the diffuser performance is optimized by changing five geometric design variables to maximize the average pressure recovery factor for two inlet boundary conditions with different swirl, corresponding to different operating modes of the hydraulic turbine. Polynomial response surfaces and radial basis neural networks are used as surrogates, while a hybrid formulation of the NSGA-IIa evolutionary algorithm and a ε-constraint strategy is applied to construct the Pareto front from the two surrogates. The proposed optimization framework drastically reduces the computational load of the problem, compared to solely utilizing an evolutionary algorithm. For the present problem, the radial basis neural networks are more accurate near the Pareto front while the response surface performs better in regions away from it. By using a local resampling updating scheme the fidelity of both surrogates is improved, especially near the Pareto front. The optimal design yields larger wall angles, nonaxisymmetrical shapes, and delay in wall separation, resulting in 14.4% and 8.9% improvement, respectively, for the two inlet boundary conditions.

  • 260.
    Marklund, Pär
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Permeability of sinter bronze friction material for wet clutches2008In: Tribology & Lubrication Technology, ISSN 1545-858X, Vol. 64, no 12, p. 34-41Article in journal (Refereed)
    Abstract [en]

    The characteristics of wet clutches are of great importance for the overall behavior of the drive trains of many modern vehicles. It is considered that the clutch characteristic is affected by the permeability of the friction material. The permeability is considered to influence both the time of engagement and the temperature in the clutch due to the lubricant flow in the permeable material. In this work, a permeability measurement method suitable for wet clutch friction materials is thus used to measure the permeability of a friction material made of sintered bronze. This friction material is suitable for applications such as limited slip differentials or other wet clutches that have to withstand high temperature and high torque transfer. The permeability is also investigated for friction materials with pressed groove patterns. Wet clutch friction material permeability is often accounted for in simulations but the method used to measure the permeability is seldom described. The permeability of the investigated friction material is shown to be so small that it hardly will affect the temperature in the material due to cooling oil flow inside the material. However, the engagement time can be influenced by the permeability. It is also shown that pressed groove patterns can seal the friction material so that it becomes almost impermeable.

  • 261. Marklund, Pär
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Permeability of sinter bronze friction material for wet clutches2007In: 62nd annual meeting of the Society of Tribologists and Lubrication Engineers 2007 : May 6 - 10, 2007, Philadelphia, Pennsylvania, USA, STLE , 2007Conference paper (Refereed)
  • 262.
    Marklund, Pär
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Permeability of sinter bronze friction material for wet clutches2008In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 51, no 3, p. 303-309Article in journal (Refereed)
    Abstract [en]

    The characteristics of wet clutches are of great importance for the overall behavior of the drive trains of many modern vehicles. It is considered that the clutch characteristic is affected by the permeability of the friction material. The permeability is considered to influence both the time of engagement and the temperature in the clutch due to the lubricant flow in the permeable material. In this work, a permeability measurement method suitable for wet clutch friction materials is thus used to measure the permeability of a friction material made of sintered bronze. This friction material is suitable for application such as limited slip differentials or other wet clutches that have to withstand high temperature and high torque transfer. The permeability is also investigated for friction materials with pressed groove patterns. Wet clutch friction material permeability is often accounted for in simulations but the method used to measure the permeability is seldom described. The permeability of the investigated friction material is shown to be so small that it will hardly will affect the temperature in the material due to cooling oil flow inside the material. However, the engagement time can be influenced by the permeability. It is also shown that pressed groove patterns can seal the friction material so that it becomes almost impermeable.

  • 263.
    Mattsson, Hans
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    On internal erosion in embankment dams: a literature survey of the phenomenon and the prospect to model it numerically2008Report (Other academic)
    Abstract [en]

    The main objective with this literature survey is to elucidate the state of the art of internal erosion in embankment dams in order to be able to formulate a research program for numerical modelling of internal erosion in a physically sound manner. Since these processes normally are localised to specific zones in a dam, the ordinary continuum approach frequently utilised in soil modelling will not, by itself, be successful. The plan of the research group is therefore to treat internal erosion numerically as a type of localisation and describe the constitutive behaviour with micromechanical models in localised zones. In the next step, the internal erosion model developed will be implemented in a mathematical consistent fashion in a continuum model, based on e.g. the finite element method. In such software, ordinary computations of stresses, strains, deformations and pore pressures in an embankment dam can be performed; results which possible lead to conclusions about the initiation of internal erosion processes. When internal erosion is initiated, the micromechanical models will describe these processes in localised zones. It was decided to restrict the literature survey to areas important for the research direction defined above. The chosen areas are thus: numerical modelling of embankment dams, internal erosion processes, embankment dam failures and accidents, filter design, micromechanical models of hydro dynamical loads on single particles and system of particles as well as micromechanical models for friction between single grains and system of grains. The most essential findings for each area, in the context of the research, will be described below. There exists much experience in the field numerical modelling of embankment dams which is exemplified by the large amount of published papers on the subject. However, the processes of internal erosion have not been modelled in a general manner, as outlined in the research idea above, in any of the papers cited in this literature survey. There are three main internal erosion processes that can initiate piping: backward erosion, concentrated leak and suffusion. Piping can occur in the embankment, through the foundation and from the embankment into the foundation. Embankment dams are normally constructed in zones of different materials. Different compressibilities of the various zones might lead to internal redistribution of stresses and uneven settlements, which might cause cracks or "soft zones" where internal erosion can be initiated. Cracks can also occur later on by hydraulic fracturing. All of that described above are examples of mechanical processes that are theoretically possible to model numerically. To receive information about potential internal erosion problems in a dam at an early stage, geophysical methods are a promising alternative or complement to numerical methods. However, much research and development remain before the results from geophysical methods utilised for permanent monitoring and surveillance of dam structures are completely trustful. It is often very difficult to determine the exact reason for a dam accident or a failure since the processes involved have a tendency to destroy evidence which might have existed. Statistical data, however, shows that failure by overtopping and piping are the most common modes of failure while failure by slides is less common. Many piping failures occur very fast, leaving a short time for proper actions. The safety of large embankment dams is strongly dependent on the reliability of the performance of their critical filters. Existing filter design criteria are in most cases empirically derived, implying that a lot of knowledge can be gained by taking a mechanical approach to the problem. More research would also be desirable in the field of ageing effects of dams and uncertainties of core/filter appearance during and after accidents, incidents etc. For this, numerical modelling also seems to be a promising approach. Continuum formulations of flow through porous media often results in equations consisting of a few unknown parameters such as the permeability. The physical background of such parameters can often be traced to the detailed flow in the pores and it is therefore in place to study the flow on this level, as well. The forces on individual particles have been exploited for certain geometries and for a number of flow conditions. We however need to investigate further higher Reynolds number flows, more complex geometries and instationary conditions. The forces from the micromechanical models must be balanced by gravity and forces that emanates from particle interactions for the dam to be stable. As a first, and most simple, criteria the size distribution of the particles being subjected to hydrodynamic pressure is compared to the pore size distribution of the porous medium. Hence the particles will move if they are small enough independent on magnitude of the force on it. In reality, however, the hydraulic forces must exceed particle interaction forces and or gravitational forces keeping the particles in place at normal conditions. The forces are strongly dependent on the size of the particles and therefore dependent on different phenomena such as cohesion, adhesion and static friction. In the final part of the literature survey a concept for numerical modelling of internal erosion is presented based on ideas that have emerged from this work. The concept involves as well mathematical developments in order to formulate a micromechanical model for internal erosion as laboratory tests. The theoretical work and the practical laboratory work should be performed simultaneously and in an interactive manner. A software containing a model that simulates internal erosion could be useful for: an increase of the knowledge about internal erosion processes, evaluating the risk for dam incidents caused by internal erosion, estimating the time for progression of internal erosion and piping, studying self-healing of leaks, changes in filter behaviour subsequent to particle accumulation and ageing effects in dams, analysing the amount of instrumentation needed in a dam and the proper location for monitoring and surveillance as well as designing dams to mention a few examples. It is therefore apparent that the route suggested has a high potential to become a tool for future improvements of dam safety.

  • 264.
    Mattsson, Hans
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Knutsson, Sven
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    On numerical modelling of internal erosion in embankment dams2009In: Proceedings 1st International Symposium on Rockfill Dams: October 18-21, 2009, Chengdu, China, 2009Conference paper (Refereed)
  • 265. Michaud, V.
    et al.
    Nordlund, Markus
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Månsson, J-E
    Capillary phenomena in liquid composite moulding2007In: 1CD-ROM proceedings of the Sixtennth International Conference on Composite Materials, July 8 - 13, 2007, Kyoto, Japan: A giant step towards environmental awareness: from green composites to aerospace / [ed] Kazuro Kageyama, Kyōto, 2007Conference paper (Refereed)
    Abstract [en]

    In liquid composite moulding, capillary phenomena take place as the fibre/air interface is progressively replaced by the fibre/resin interface. These effects are often neglected when computing the flow front progression into the fibre preform, because the surface tension of the resins is low. However, these are recognized to exert an influence on the final void content of the part. In this article, we present experimental results from unidirectional infiltration of an epoxy resin under constant flow rate into non-crimp fabrics. The inlet pressure rise is shown to deviate from linearity, indicating a progressive saturation. A multiphase flow approach is proposed to model infiltration, assuming saturation curves and relative permeability dependence on saturation based on soil science literature. Numerical results using a FEM code show trends that are in good qualitative agreement with experimental results. The interest and validity of this approach is then discussed.

  • 266.
    Misiulia, Dzmitry
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Effects of the inlet angle on the collection efficiency of a cyclone with helical-roof inlet2017In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 305, p. 48-55Article in journal (Refereed)
    Abstract [en]

    The effects of inlet angle on the collection efficiency of a cyclone with helical-roof inlet have been computationally investigated using Large Eddy Simulations with the dynamic Smagorinsky-Lilly subgrid-scale model for five different inlet angles (7°, 11°, 15°, 20° and 25°). Forty thousand individual particles were tracked through the unsteady flow field using the Lagrangian approach. In order to reveal the collection efficiency of a cyclone with helical-roof inlet properly, simulation time should not be < 3.5 times the average flow residence time. Particles which diameter is close to the cyclone cut size have the longest residence times while particles of 10–25 μm in diameter have the shortest. Based on the simulations, expressions for the cut size and Euler number normalized with the mean axial velocity in a cyclone with helical-roof inlet of different inlet angles are derived. The results show that, increasing the inlet angle increases the cyclone cut size and as a result reduces cyclone collection efficiency. At the same time, it decreases the cyclone pressure drop coefficient (Euler number) leading to lower pressure losses. For most cases where high separation efficiency at moderate pressure drop is required the optimum inlet angle is in the range 10–15°.

  • 267.
    Misiulia, Dzmitry
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Large Eddy Simulation Investigation of an Industrial Cyclone Separator Fitted with a Pressure Recovery Deswirler2017In: Chemical Engineering & Technology, ISSN 0930-7516, E-ISSN 1521-4125, Vol. 40, no 4, p. 709-718Article in journal (Refereed)
    Abstract [en]

    A cyclone fitted with a deswirler of original design has been investigated by means of large eddy simulation. Installation of the deswirler reduces significantly the positive static pressure near the wall as well as the negative static pressure in the central region. It also decreases the maximum tangential velocities in the main separation zone. The deswirler enables a substantial reduction of the backward flow at the gas outlet and a more uniform distribution of the axial velocities at the gas outlet. It also considerably reduces pressure losses in the vortex finder lowering the cyclone pressure drop by almost about one third but it deteriorates the collection efficiency of particles with diameters of less than 8 µm, thus increasing the cut size.

  • 268.
    Misiulia, Dzmitry
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Computational Investigation of an Industrial Cyclone Separator with Helical-Roof Inlet2015In: Chemical Engineering & Technology, ISSN 0930-7516, E-ISSN 1521-4125, Vol. 38, no 8, p. 1425-1434Article in journal (Refereed)
    Abstract [en]

    An industrial cyclone separator with helical-roof inlet TsN-11 has been numerically investigated as to pressure and flow field, pressure drop, fractional efficiency, and particle trajectories inside the cyclone. The turbulence was modeled with Reynolds stresses and large eddy simulations (LES) based on three different subgrid-scales (SGS). The results with the different setups were compared to experimental data from previous studies. For a proper calculation of the flow field, LES combined with a dynamic SGS model was used for predicting cyclone performance. Individual particles were tracked through the unsteady flow field using the Lagrangian approach. The results of the numerical calculations of the tangential and axial velocity, pressure drop, and cut size are in good agreement with experimental measurements.

  • 269.
    Misiulia, Dzmitry
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Effects of the inlet angle on the flow pattern and pressure drop of a cyclone with helical-roof inlet2015In: Chemical engineering research & design, ISSN 0263-8762, E-ISSN 1744-3563, Vol. 102, p. 307-321Article in journal (Refereed)
    Abstract [en]

    The effects of inlet angle on the flow pattern and pressure drop in cyclones have been numerically investigated using Large Eddy Simulations with the dynamic Smagorinsky-Lilly subgrid-scale. Five cyclones with helical-roof inlets of different inlet angles and five cyclones with tangential inlets of different inlet heights at the same other geometric dimensions are considered. The results show that, increasing the inlet angle as well as the inlet height (inlet area) decreases the absolute values of positive (close to the cyclone wall) and negative (in the central region) static pressure and tangential velocity in the cyclone body that will probably reduce the collection efficiency. Also, increasing the inlet angle reduces the gas flow rates along the cyclone axis in both downward (outer) and upward (inner) vortices and increases the maximum radial velocity under the vortex finder that can enhance the number of small particles entrained by the gas flow and transferred from that region into the vortex finder and negatively affect the overall collection efficiency. The cyclone pressure drop is mainly generated by the losses in the cyclone body (under the vortex finder) and in the vortex finder. There is a significant decrease in pressure drop with increase of inlet angle. Based on the simulations an expression for the dimensionless pressure drop normalized by the inlet velocity for the cyclone with helical-roof inlet of different inlet angles is derived. Cyclones with helical-roof inlets have a higher aerodynamic efficiency as compared to cyclones with tangential inlets, and the highest aerodynamic efficiency was reached with an inlet angle of 20°.

  • 270.
    Misiulia, Dzmitry
    et al.
    Department of Machines and Apparatus for Chemical and Silicate Production, Belarusian State Technological University.
    Antonyuk, Sergiy
    Institute of Particle Process Engineering, University of Kaiserslautern.
    Andersson, Anders Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Tord Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Effects of deswirler position and its centre body shape as well as vortex finder extension downstream on cyclone performance2018In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 336, p. 45-56Article in journal (Refereed)
    Abstract [en]

    The performance of a cyclone is studied when changing the position of the deswirler in the vortex finder, its centre body shape and a downstream vortex finder extension. This is done with simulations applying a Reynolds stress model for the turbulence. An extension of the vortex finder (from 2.64 dvf to 6.8 dvf) has almost no effect on cyclone pressure drop or collection efficiency. Moreover, the extension does not affect the pressure losses in the vortex finder. The closer the deswirler is installed to the vortex finder inlet the more significant is its effects on cyclone performance. A streamlined ellipsoidal shape of the deswirler centre body is preferable to a cylindrical one since it leads to lower pressure losses. Installation of the deswirler with a streamlined ellipsoidal centre body 2.64 diameters downstream the vortex finder inlet reduces pressure losses in the vortex finder by 74% as compared to a standard set-up. This leads to a 32% reduction in total pressure drop without deteriorating the separation capability of the cyclone.

  • 271. Nordlund, Markus
    et al.
    Fernberg, S.P.
    SICOMP AB, Swedish Institute of Composites.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Particle deposition mechanisms during processing of advanced composite materials2007In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 38, no 10, p. 2182-2193Article in journal (Refereed)
    Abstract [en]

    Liquid composite moulding of advanced composite materials often comprises infiltration of a particle-filled resin into a multi-scale porous fabric. These injections/infusions are subject to severe particle depositions inside the reinforcement, leading to undesired inhomogeneous mechanical and functional properties. Hence, the mechanisms for particle depositions are investigated by detailed meso-scale experiments, analysed by microscopic imaging and micro-particle image velocimetry, and macroscopic infusions of a biaxial non-crimp fabric. It is shown that two main particle deposition mechanisms are filtration during fibre bundle impregnation and filtration induced by stationary flow through fibre bundles. It is also clarified where in the reinforcement the particles will deposit. Finally, a number of suggestions on how to process advanced composite materials with a more homogeneous particle distribution are launched.

  • 272. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    An investigation of particle deposition mechanisms during impregnation of dual-scale fabrics with micro particle image velocimetry2010In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 31, no 7, p. 1232-1240Article in journal (Refereed)
    Abstract [en]

    Injection moulding processing of composite materials most often includes infiltration of a thermoset resin into a multi-scale porous fabric. Controlling the fluid flow within the multi-scale fabric is essential for the quality of the final composite material, since the transport of fluid between regions with different scales is of importance for phenomena such as void formation and filtration of particle doped resins. Hence, the transient flow behaviour in dual scale porous media is investigated in detail with Micro Particle Image Velocimetry. These experiments show that the fluid transport between the two scales can be controlled by the injection velocity. Validation of the measured velocity fields furthermore shows excellent agreement with theory and that transport between the two scales can be substantial at the flow front but negligible up-stream it. POLYM. COMPOS

  • 273. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Effect of geometrical features of non-crimp fabrics on the permeability2004In: From nano-scale interactions to engineering structures: ECCM 11, 11th European Conference on Composite Materials ; May 31 - June 3, 2004, Rhodes, Greece / [ed] Costas Galiotis, Rhodos, 2004Conference paper (Refereed)
  • 274. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Effect of multi-scale porosity in local permeability modelling of non-crimp fabrics2008In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 73, no 1, p. 109-124Article in journal (Refereed)
    Abstract [en]

    The influence of multi-scale porosity of fibre reinforcements on local permeability is investigated, in order to determine the possibility of simplifying permeability models for more efficient permeability calculations. Unit cell models of a biaxial Non-Crimp Fabric are developed and used to investigate, whether or not the porous bundles can be excluded, when modelling the local permeability. Numerical accuracy of calculations is controlled to guarantee the quality of the results and the conclusions drawn from them. It is found that fibre bundles with high fibre density can be excluded from permeability models, while bundles with low fibre volume fractions need to be included. A new method to model the local permeability of multi-scale reinforcements is developed and verified for low fibre density in the bundles. In this method, the effects of the flow inside the fibre bundles are included through modifications of the boundary conditions of a single-scale model representing the interbundle regions. The local permeability of multi-scale reinforcements can, therefore, be calculated by models with simplified fluid domains for all fibre bundle porosities, instead of being calculated by models consisting of the entire multi-scale geometry.

  • 275. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental study of particle filtration in dual-scale porous media2006In: 2nd International Symposium Nanostructured and Functional Polymer-based Materials and Composites, Lyon, May 29 - 31,2006, Impact press, 2006Conference paper (Refereed)
  • 276. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical study of the local permeability of noncrimp fabrics2005In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 39, no 10, p. 929-947Article in journal (Refereed)
    Abstract [en]

    Noncrimp stitched fabrics (NCFs) are often used as reinforcing materials in high-performance composite materials. Prediction models of the processing stage of the manufacturing are highly desirable in order to enhance the control of the process and enable the production of materials with higher quality. In NCFs, layers of parallel fiber bundles consisting of a large number of fibers are stitched together with other layers to form a network of interbundle channels in different directions. In earlier works, numerical simulations on unit cells had been performed in order to predict the global permeability of NCFs. It was shown that features like the thread influence the local permeability of the unit cells and therefore, the local permeability distribution of a fabric also. Furthermore, this influences the global permeability of the entire fabric. In the present paper, different geometrical features are therefore studied in order to investigate their influence on the local permeability within an NCF. The stitching process in addition to the interbundle channels, gives rise to two geometrical features, the thread which penetrates the channels and the crossing of fibers between two neighboring fiber bundles. The influences of these two features on the local permeability are studied together with variations of other geometrical parameters of the fabric. Computational Fluid Dynamics are used for the flow simulations in order to calculate the local permeability for the different unit cells. To ensure quality and trust, the numerical accuracy of the simulations is also studied. This work proves that the thread and the crossings, as well as the variations of the width and the height of the interbundle channels, have great influence on the local permeability. Prediction models therefore, have to take these features as well as geometry distortions, which influence the local permeability distribution, into account in order to make accurate predictions of the global permeability of a fabric.

  • 277. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Permeability network model of non-crimp fabrics2005In: Fifteenth international conference on composite materials (ICCM-15): extended abstracts : 27 June - 1 July 2005, Durban, South Africa / [ed] Viktor E. Verijenko, Durban: Centre for Composite and Smart Materials and Structures, University of KwaZulu-Natal , 2005Conference paper (Refereed)
  • 278. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Jakovics, A.
    University of Latvia.
    Permeability network model for non-crimp fabrics2006In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 37, no 6, p. 826-835Article in journal (Refereed)
    Abstract [en]

    In this work a global permeability model is developed and applied to a biaxial Non-crimp stitched fabric (NCF). This model focuses on a detailed meso-scale description of the fabric geometry, which takes into account the local permeability distribution in a fabric due to perturbations of the geometry as well as the geometrical features which arise from the stitching process. It is shown in this work that these features significantly affects the global permeability. The influence of the amount and type of perturbation of a fabric is also studied in this work. It is shown that perturbation of the fabric geometry affect the global permeability but not as much as the stitching process. The model developed is finally validated with experimental permeability data and it is suggested how to use the model for an arbitrary lay-up.

  • 279. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Jakovics, Andris
    Application of permeability network model to non-crimp fabrics2004In: The XIII International Conference on Mechanics of Composite Materials, 2004Conference paper (Refereed)
  • 280. Nordlund, Markus
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Michaud, V.
    Månson, J-A
    Wetting dynamics of nano-charged resins in multi-scale porosity2005In: Proceedings of the International Conference on Science and Technology of Composite Materials: COMAT 2005, 2005Conference paper (Refereed)
  • 281.
    Näsström, Mats
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Karlberg, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Turesson, Lena
    Luleå University of Technology, Professional Support, VSS TVM.
    Palmblad, Marie-Louise
    Luleå University of Technology, Professional Support, VSS TVM.
    Projekt: Fastelaboratoriet - VINNEXC2007Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    Fastelaboratoriet är ett VINN Excellence Center för innovation inom Funktionella Produkter. Centret skapades till minne av innovatören Rolf Faste som under många år var verksam vid Stanford University i Kalifornien, USA

  • 282.
    Odemark, Ylva
    et al.
    Vattenfall Research & Development.
    Green, Torbjörn
    Angele, Kristian
    Vattenfall Research & Development.
    Westin, Johan
    Vattenfall Research & Development.
    Alavyoon, Farid
    Forsmarks kraftgrupp AB.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    High-cycle thermal fatigue in mixing tees: new large-eddy simulations validated against new data obtained by PIV in the Vattenfall experiment2009In: Proceedings of the 17th International Conference on Nuclear Engineering - 2009: presented at 17th International Conference on Nuclear Engineering, July 12 - 16, 2009, Brussels, Belgium, New York: American Society of Mechanical Engineers , 2009, p. 775-785Conference paper (Refereed)
    Abstract [en]

    New data was obtained for a previously studied T-junction experimental setup [1] for a range of flow ratios between hot and cold flows in order to validate new Large Eddy Simulations (LES). The instantaneous velocity field downstream of the T-junction was measured with two-component Particle Image Velocimetry (PIV) in several horizontal and vertical planes at the centre line downstream of the T-junction. The generated PIV database enables a thorough validation of CFD turbulence statistics. The turbulence statistics are shown to be well predicted despite the fact that the mesh in the LES is rather coarse. By usage of time resolved PIV the temporal evolution of the predominant low frequent large-scale structures, responsible for much of the mixing and the high amplitude temperature fluctuations on the walls, were captured. Those structures are, however, weaker in LES than in PIV, being in line with the fact that the wake region behind the penetrating vertical hot jet is underpredicted in LES. Tests regarding the influence of the LES-results to the shape of the inlet boundary conditions (developed or flat symmetric mean-velocity profiles) were carried out and the sensitivity in the results was shown to be small. Furthermore, the results show good agreement with the experimental data independent of the flow ratio between the hot and the cold flows.

  • 283. Odenberger, Torbjörn
    et al.
    Andersson, Magnus
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental flow-front visualisation in compression moulding of SMC2004In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 35, no 10, p. 1125-1134Article in journal (Refereed)
    Abstract [en]

    This work is primarily focused on experimental visualisation of the flow during mould closure in compression moulding of sheet moulding compound. Circular plates are manufactured with industry scale equipment at close to production conditions. Special attention is given to the advancing flow front, for which the full complexity is captured by means of continuous high resolution close-up monitoring. From the experimental visualisation of the flow front, three phases are defined, namely squish, flow, and boiling. During the initial phase, squish, outer layers do not remain outer layers, the actual flow is very complex and air is likely to be entrapped. The governing process parameters during this phase are mould temperature, mould closing speed and amount of preheating in the mould. During the second phase, flow, the flow is stable and seemingly viscous. During the last phase, boiling, bubbles are observed in the low pressure region at the flow front, favouring the void content both internally and on the surface. Based on a chemical analysis including mass spectrometry and thermogravimetry, the gas is probably styrene.

  • 284. Odenberger, Torbjörn
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Inverse modelling of compression moulding of SMC with usage of computational fluid dynamics2006In: Fifteenth International Conference on Composite Materials (ICCM-15): [... held on 27 June - 1 July 2005 in Durban, South Africa] / [ed] V.E. Verijenko, Durban: Centre for Composite and Smart Materials and Structures, University of KwaZulu-Natal , 2006Conference paper (Refereed)
  • 285. Olofsson, Kenneth
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Strömbeck, A.
    Measurement of micro scale defects in polymer composites2001In: Proceedings of the 13th International Conference on Composite Materials: Beijing, June 25-29, 2001 / [ed] Y. Zhang, Beijing: Scientific and Technical Documents Publishing House , 2001Conference paper (Refereed)
  • 286. Olsson, Jimmy
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Olofsson, K.
    Swerea SICOMP AB.
    Process study on compression moulding of SMC using factorial design2008In: 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 , 2008Conference paper (Refereed)
    Abstract [en]

    During compression moulding of sheet moulding compounds, voids are formed that can deteriorate the properties of the final product. A large number of processing and material parameters can however be tuned in order to reduce the amount of voids. A factorial design is here applied to plan an experimental series where, in particular, vacuum assisted mouldings are carried out in a circular shaped mould. One result is that the electrical insulation can be considerably improved by choosing optimal processing conditions. Another is that the size of weld lines can be reduced in the same fashion.

  • 287. Olsson, Jimmy
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Olofsson, Kurt
    Swerea SICOMP AB.
    Compression moulding of SMC: coupling between the flow and the local void contents2009In: ICCM 17, Edinburgh: 17th International Conference on Composite Materials ; 27 Jul 2009 - 31 Jul 2009, Edinburgh International Convention Centre, Edinburgh, UK, London: IOM Communications , 2009Conference paper (Refereed)
    Abstract [en]

    During compression moulding of sheet moulding compound (SMC), voids are formed that can deteriorate the properties of the final product. Here, experimental work and CFD-simulations have been carried out in order to increase the knowledge of the SMC compression moulding behaviour which highly affects the quality of the final products.

  • 288. Olsson, Jimmy
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Olofsson, Kurt
    Swerea SICOMP AB.
    Design of experiment study of compression moulding of SMC2009In: Plastics, rubber and composites, ISSN 1465-8011, E-ISSN 1743-2898, Vol. 38, no 9/10, p. 428-433Article in journal (Refereed)
    Abstract [en]

    The effect of vacuum assistance, mould temperature and ram velocity on the void transport and flow behaviour for sheet moulding compound (SMC) have been investigated with a design of experiment approach of the compression moulding phase. The relative amount of voids has been quantified with a high voltage insulation test and the flow behaviour has been quantified with image analysis of samples moulded with coloured SMC. In conclusion, the setting of high vacuum, low ram velocity and low mould temperature creates a homogeneous flow and minimises the amount of voids.

  • 289.
    Olsson, Jimmy
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nyman, Tonny
    Saab Aeronautics, SE-582 54 Linköping, SWEDEN.
    Flow and heat transfer inside an autoclave2012In: Proceedings of the 11th International Conference on Flow Processing in Composite Materials, 2012Conference paper (Other academic)
    Abstract [en]

    This work, that involves both experiments and numerical simulations, concerns autoclave molding. An autoclave is basically a pressure vessel, where the entrapped and often highly compressed gas is heated and circulated in order to heat the components that have been placed inside the vessel. In the autoclaveprocess, the desirable state would be that an even and optimal temperature existed in the whole part that is manufactured. Unfortunately, this is not always the case. All in all we need to get a better understanding of the flow inside an autoclave and the convective heat transfer from the heated gas to the composite components. In this work we have therefore investigated the flow behavior by performing qualitative measurements with particle image velocimetry inside an autoclave. The concept is to dope the gas within the autoclave with smoke and illuminate the smoke with a thin sheet of laser light. Captured images of the moving smoke are then cross correlated to give velocity fields. We have also investigated the heat transfer to the tool by measuring the temperature at multiple locations during heating. The obtained velocity field is used to produce inlet condition for the simulations, performed with Computational Fluid Dynamics, which subsequently are compared with the experimentally obtained tool temperature. The simulation technique may then be used to optimize both the tools, and the actual location of the tools inside the autoclave in order to improve quality and reduce costs.

  • 290.
    Pavasson, Jonas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Karlberg, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Larsson, Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Johansson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Challenges and opportunities within simulation-driven functional product development and operation: Special Session: Product Development for Through-Life Engineering Services2014In: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 22, p. 169-174Article in journal (Refereed)
    Abstract [en]

    The product development process at industrial companies has traditionally focused on hardware-oriented solutions. Business strategies strive towards more service-oriented solutions e.g., functional product business models. In this paper two case studies are developed and the objective is to highlight important challenges and opportunities by implementing a simulation-driven strategy in functional product development and operation. It can be concluded that challenges and opportunities within simulation-driven functional product development and operation are related to both quality and management of the simulations. With the proposed strategies for validation and coupling of the simulations, some of the challenges within functional product development can be overcome.

  • 291.
    Pettersson, Patrick
    et al.
    Metso Paper Sundsvall.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wassvik, Elianne
    Modeling pressure distribution in a belt press during manufacture of fiberboards2007In: Wood and Fiber Science, ISSN 0735-6161, Vol. 39, no 3, p. 493-501Article in journal (Refereed)
    Abstract [en]

    When forming fiberboards, a large amount of air is evacuated from the dry fiber mat and the fibers are subjected to forces generated by the flow. If the forces become too strong, the fiber mat bursts and the process stops with financial loss as a result. A simplified model for the pressure field during the pressing has been derived, by starting from first principles. This model indicates that the velocity of the belt can be increased as long as the length of the press is increased, or the viscosity of the penetrating fluid is decreased in a prescribed manner. The model furthermore suggests that the pressure distribution will be unaffected by variations in the basis weight of the fiber mat as long as the basis weight is matched with an equal change in the density of the fibers. Furthermore, by numerically deriving the pressure field as a function of boundary conditions, it is shown that minor variations in the pressure at the nip may result in huge differences in the pressure at the entrance of the press. In a validating procedure, it is shown that model parameters can be adjusted in a physically reasonable way to obtain acceptable agreement with experimental data, but also that the model must be considerably improved in order to obtain quantitative conformity.

  • 292. Pettersson, Patrik
    et al.
    Lindgren, Kristian
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wikström, Tomas
    Development of material models for dewatering of pulp suspension2008In: 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 , 2008Conference paper (Refereed)
    Abstract [en]

    During the process of making pulp from wood, free fibers are mixed in a pulp suspension containing a large amount of water (98-50% by mass), wood fibers and often some processing chemicals. The suspension in this process is gradually cleaned from dissolved material. The suspension can be washed in a displacement washing step where the dirty fluid is replaced with a cleaner one. or by a compression step which increases the consistency of the suspension. To reduce costs and to increase the production rate of pulp and paper overall it is important to understand the interaction between fluid and fibers in such processes. During dewatering and washing, fibers are exposed to a drag force from the fluid. As the concentration of fibers increases this drag force and, consequently, the pressure generated from it become proportional to the permeability of the fiber network formed. When contact between fibers increases, an additional pressure emanates caused by bending and compressing of the fibers. By comparing experiments to a numerical model this study shows that for high dewatering velocities the resulting force required to dewater a suspension cannot be found by adding these two pressures. One reason for this may be that intra-fiber flows contribute to the force. Another explanation can be related to reinforcement

  • 293. Pettersson, Patrik
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wikström, T.
    Metso Paper Sundsvall.
    A method to measure the permeability of dry fiber mats2006In: Wood and Fiber Science, ISSN 0735-6161, Vol. 38, no 3, p. 417-426Article in journal (Refereed)
    Abstract [en]

    Close to the finalization of the medium density fiberboard process, a fairly thick bed of loosely entangled fibers is compressed in a belt-press to often less than a tenth of its original unstressed thickness. This single unit operation is very important to consider when the manufacturing process of the boards is to be optimized. Despite this, there is a lack of knowledge of the interaction between the fiber mat strength and how the fluid flows through it, i.e. de-aeration. Thus, it is of greatest importance to find reliable methods for studying this stage of the manufacturing process. Following this quest, a method is developed with which the gas permeability of fiber mats can be measured. The method offers the potential to measure the permeability at different flow rates and thus at arbitrary pressure gradients through the material. The method is successfully validated with a porous reference material consisting of polymer spheres, and it is shown that the flow follows Darcy's law at the flow rates of interest. Finally, the method is demonstrated by a presentation of permeability measurements on fiber mats consisting of spruce fibers.

  • 294. Pettersson, Patrik
    et al.
    Wikström, T.
    Metso Paper Sundsvall.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Method for measuring permeability of pulp suspension at high basis weights2008In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 34, no 4, p. 191-197Article in journal (Refereed)
    Abstract [en]

    During the formation of pulp to paper, a large amount of water is added to dilute the pulp in order to obtain a homogenous material. This water call be mechanically and/or thermodynamically removed by different process solutions. The pulp suspension flows through various process equipment that influence the pulp suspension by changing its properties before the pulp suspension finally becomes paper. It is important to understand the mechanisms behind the transport path of water in this process in order to reduce cost and to increase the production rate of pulp and paper. The resistance to flow must be known in order to describe the flow path and the corresponding pressure drop in dewatering equipment in a pull.? mill. For networks with a complex geometry, a reliable method is to measure the resistance to flow at discrete points and to fit suitable resistance models to the results obtained. The objective of this study is to investigate how the history of pulp suspensions affects their permeability. A device for measuring the permeability of various pulp suspensions at high basis weights is developed and validated. Then the permeability of a number of virgin pulp species is measured. Some of the suspensions are then circulated in a closed flow loop and permeability is measured as a function of the number of loops. The results from two separate test's show that a basis weight variation and a different process treatment of the pulp suspension do not influence permeability.

  • 295.
    Rafols, Francesc Perez
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wall, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A stochastic two-scale model for pressure-driven flow between rough surfaces2016In: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 472, no 2190, article id 20160069Article in journal (Refereed)
    Abstract [en]

    Seal surface topography typically consists of global-scale geometric features as well as local-scale roughness details and homogenization-based approaches are, therefore, readily applied. These provide for resolving the global scale (large domain) with a relatively coarse mesh, while resolving the local scale (small domain) in high detail. As the total flow decreases, however, the flow pattern becomes tortuous and this requires a larger local-scale domain to obtain a converged solution. Therefore, a classical homogenization-based approach might not be feasible for simulation of very small flows. In order to study small flows, a model allowing feasibly-sized local domains, for really small flow rates, is developed. Realization was made possible by coupling the two scales with a stochastic element. Results from numerical experiments, show that the present model is in better agreement with the direct deterministic one than the conventional homogenization type of model, both quantitatively in terms of flow rate and qualitatively in reflecting the flow pattern.

  • 296.
    Sam, Ali al
    et al.
    Lund University, Division of Fluid Mechanics.
    Andersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Szász, Robert-Zoltán
    Lund University, Division of Fluid Mechanics.
    Hellström, Gunnar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Revstedt, Johan
    Lund University, Division of Fluid Mechanics.
    Measurement and simulation of turbulent flow over rough surface2014Conference paper (Refereed)
  • 297.
    Sarkar, Chiranjit
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundström, Staffan T.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical simulations of lubricating grease flow in a rectangular channel with and without restrictions2018In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 61, no 1, p. 144-156Article in journal (Refereed)
    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.

  • 298. Synnergren, Per
    et al.
    Larsson, Linda
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Digital speckle photography: visualization of mesoflow through clustered fiber networks2002In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 41, no 7, p. 1368-1373Article in journal (Refereed)
    Abstract [en]

    Digital speckle photography (DSP) is used for velocity field measurements inside a fiber network. The width of the channels in which the flow is measured is typically less than 1 mm. Therefore a microscope is used to image the fiber network. When we sample 30 images/s and separate the moving parts of the images from the stationary parts, the velocity field can be deduced with DSP

  • 299.
    Teng, Ziyan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Johansson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, Daniel
    Luossavaara-Kiirunavaara AB.
    CFD Simulation of Jet Mixing with Asymmetric Co-flows in a Down-scaled Rotary Kiln Model2016In: Proceedings of the ASME 2016 International Mechanical Engineering Congress and Exposition, ASME Press, 2016, Vol. 7, article id IMECE2016-65637Conference paper (Refereed)
    Abstract [en]

    Rotary kilns used in the iron pellet production in the grate-kiln pelletizing process normally have two asymmetric secondary air channels. The primary jet is ejected from a burner located in the middle of a back plate. As a consequence of the high flow rates and irregular-shaped secondary air channels, the aerodynamics in the kiln is strongly connected to the combustion and sintering performance. In this work a Computational Fluid Dynamics study is performed on a downscaled, simplified kiln model established in earlier numerical and experimental work. Comparisons are made with the experiment and among three turbulence models, the standard k-ε model, a k-ε model modified for turbulent axisymmetric round jets and Speziale-Sarkar-Garski Reynolds Stress Model (SSG-RSM hereafter). Recirculation regions with negative axial velocity are found at the upper side of the kiln and behind the back plate. Results from the standard k-ε model have the best fit to the experimental data regarding the centerline decay and the jet spreading of the velocity. The spreading rate of the scalar concentration calculated from the results with the modified k-ε model and the SSG-RSM fit better with the experiment, but they both underestimate the centerline decay and the spreading of the velocity. The modified k-ε model yields a more physical and realistic flow field compared to the standard k-ε model, and the results are close to those obtained with the SSG-RSM. Unlike the isotropic development of the jet predicted with the standard k-ε model, the modified k-ε model and the SSG-RSM show different development of the jet in the horizontal and vertical directions.

  • 300.
    Teng, Ziyan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Larsson, Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, B. Daniel
    Luossavaara-Kiirunavaara AB, Kiruna SE-981 86, Sweden.
    The Effect of Reynolds Number on Jet in Asymmetric Co-Flows: A CFD Study2018In: International Journal of Chemical Engineering, ISSN 1687-806X, E-ISSN 1687-8078, article id 1572576Article in journal (Refereed)
    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

34567 251 - 300 of 327
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf