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  • 1.
    Altimira, Mireia
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Teaching Research Methodologies2016Ingår i: INTED2016 Proceedings, IATED , 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents the methodology employed in the Research Methodology course, part of the Master Program in Engineering Mechanics of the Royal Institute of Technology (KTH). As a higher education institution, KTH aims at excellence in both generation and dissemination of knowledge. Even though these two activities are traditionally seen as independent –or even mutually exclusive-, there is a positive correlation between performance in research andin pedagogical activities, reinforced by the fact that inquiry-based or researchbased learning activities enhance deep learning among the students. The course Research Methodology in Engineering Mechanics poses a unique opportunity to engage the students to research in different areas through diversity-oriented learning activities.The course’s main learning outcome is that the students become acquainted with the most common concepts and research methodologies used in the fields of Fundamental Mechanics, Solid Mechanics, Fluid Mechanics, Acoustics and Biomechanics. After the completion of the course, the student should also be able to identify and analyze the methodologies in a given published work.The course consists of 9 lectures and a group project, with an estimation of the total dedication time of 80h (3hp). One lecture is focused on research ethics;while in the other 8 researchers from KTH present their areas of expertise, introducing the most relevant methodologies applied. The attendance is about40 students.In the last two years, and based on the course assessment survey, the structure of the course has been continuously shifting from traditional lectures to cover a broader range of teaching activities. In this way, different learning styles are covered and the learning outcomes can be achieved by as many students as possible. In this regard, traditional lectures are combined with problem-based or case-based lectures, and role-play. Additionally, in the content of the lectures we also try to keep a balance between experimental and numerical research methods of the different disciplines, in such a way that the students get a holistic view of the research in that particular field.This project involves reading a research journal article in the subject of engineering mechanics and presenting, in written and oral form, a critical analysis of the methodologies employed. In the beginning of their project, the students give an oral presentation of their article to another group. At the end of this activity, each group is asked to mention a positive aspect of the presentation they just heard and something that they believe should be improved. As an additional task, each group is asked to peer-review another group’s report. To do so, the students are given a document with some guidelines and evaluation criteria. Special instructions are given to make sure positive feedback is also included in the review. With this, the students get to read the work of others, learn to apply quality criteria and give feedback, and self-reflect on their own work after the review process.

  • 2.
    Berg, Niclas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Biomekanik.
    Blood flow simulations of the renal arteries - effect of segmentation and stenosis removalIngår i: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Patient specic based simulation of blood flows in arteries has been proposed as a future approach for better diagnostics and treatment of arterial diseases.The outcome of theoretical simulations strongly depends on the accuracy in describing the problem (the geometry, material properties of the artery and of the blood, flow conditions and the boundary conditions). In this study, the uncertainties associated with the approach for a priori assessment of reconstructive surgery of stenoted arteries are investigated. It is shown that strong curvature in the reconstructed artery leads to large spatial- and temporal-peaks in the wall shear-stress. Such peaks can be removed by appropriate reconstruction that also handles the post-stenotic dilatation of the artery. Moreover, it is shown that the effects of the segmentation approach can be equally important as the effects of using advanced rheological models. Unfortunately, this fact has not been recognized in the literature up to this point, making patient specic simulations potentially less reliable.

  • 3.
    Berg, Niclas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, BioMEx.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Centra, BioMEx. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, BioMEx. KTH Mech, Linne FLOW Ctr, BioMEx, SE-10044 Stockholm, Sweden..
    Blood Flow Simulations of the Renal Arteries - Effect of Segmentation and Stenosis Removal2019Ingår i: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 102, nr 1, s. 27-41Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Patient specific based simulation of blood flows in arteries has been proposed as a future approach for better diagnostics and treatment of arterial diseases. The outcome of theoretical simulations strongly depends on the accuracy in describing the problem (the geometry, material properties of the artery and of the blood, flow conditions and the boundary conditions). In this study, the uncertainties associated with the approach for a priori assessment of reconstructive surgery of stenoted arteries are investigated. It is shown that strong curvature in the reconstructed artery leads to large spatial- and temporal-peaks in the wall shear-stress. Such peaks can be removed by appropriate reconstruction that also handles the post-stenotic dilatation of the artery. Moreover, it is shown that the effects of the segmentation approach can be equally important as the effects of using advanced rheological models. This fact has not been recognized in the literature up to this point, making patient specific simulations potentially less reliable.

  • 4.
    Berg, Niclas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Biomekanik.
    Flow characteristics and coherent structures in a centrifugal blood pump2019Ingår i: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 102, nr 2, s. 469-483Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Blood clot formation can be initiated by local flow conditions where regions of high shear and long residence time regions, such as flow separation and stagnation, have been identified as risk factors. This study highlights coherent structures,some of which not yet considered in the literature that may contribute to blood clot formation in the ECMO (Extra Corporeal Membrane Oxygenator) circuit. The centrifugal ECMO pump investigated in this study is compact and delivers adequate volume of blood with relatively high pressure in order to compensate for the large pressure drop in the membrane oxygenator. These requirements lead to regions with high shear in several different parts of the pump. In the narrow gap between the pump house and the impeller body (the magnet) a Taylor-Couette-like flow is observed with azimuthally aligned wavy vortices, which are also pushed towards the bottom of the pump-house by the flow generated by the blades. At the bottom gap between the impeller house and the pump house one finds spiraling flow structures, due to the rotation of the former structure. Separation bubbles are found near the tongue of the pump and at the lee sides of the blades. Such vortical structures have in literature been identified as regions where platelets may be activated whereby clots may develop.

  • 5.
    Berg, Niclas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Biomekanik.
    Influence of red blood cell polydispersity on blood rheology and platelet marginationManuskript (preprint) (Övrigt vetenskapligt)
  • 6.
    Broman, Lars Mikael
    et al.
    Karolinska Univ Hosp, ECMO Ctr Karolinska, Dept Pediat Perioperat Med & Intens Care, Eugeniavagen 23, S-17176 Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden.;EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England..
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, BioMEx.
    Westlund, C. Jerker
    Karolinska Univ Hosp, ECMO Ctr Karolinska, Dept Pediat Perioperat Med & Intens Care, Eugeniavagen 23, S-17176 Stockholm, Sweden..
    Gilbers, Martijn
    Maastricht Univ, Dept Cardiothorac Surg, Heart & Vasc Ctr, Cardiovasc Res Inst Maastricht CARIM,Med Hosp, Maastricht, Netherlands.;Maastricht Univ, Dept Physiol, Maastricht, Netherlands..
    da Camara, Luisa Perry
    Hosp Curry Cabral, Ctr Hosp Lisboa Cent, Lisbon, Portugal..
    Swol, Justyna
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Paracelsus Med Univ, Dept Pulmonol, Intens Care Med, Nurnberg, Germany..
    Taccone, Fabio S.
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;ULB, Dept Intens Care, Hop Erasme, Brussels, Belgium..
    Malfertheiner, Maximilian V.
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Univ Med Ctr Regensburg, Dept Internal Med Cardiol & Pneumol 2, Regensburg, Germany..
    Di Nardo, Matteo
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Childrens Hosp Bambino Gesu, IRCCS, Pediat Intens Care Unit, Rome, Italy..
    Vercaemst, Leen
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Univ Hosp Gasthuisberg, Dept Perfus, Leuven, Belgium..
    Barrett, Nicholas A.
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Guys & St Thomas NHS Fdn Trust, Dept Crit Care, London, England.;Guys & St Thomas NHS Fdn Trust, Severe Resp Failure Serv, London, England..
    Pappalardo, Federico
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Univ Vita Salute San Raffaele, Adv Heart Failure & Mech Circulatory Support Prog, Hosp San Raffaele, Milan, Italy..
    Belohlavek, Jan
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Charles Univ Prague, Gen Univ Hosp Prague, Dept Cardiovasc Med, Dept Med 2, Prague, Czech Republic.;Charles Univ Prague, Fac Med 1, Prague, Czech Republic..
    Mueller, Thomas
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Univ Med Ctr Regensburg, Dept Internal Med Cardiol & Pneumol 2, Regensburg, Germany..
    Belliato, Mirko
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Fdn IRCCS Policlin San Matteo, UOC Anestesia & Rianimaz 1, Pavia, Italy..
    Lorusso, Roberto
    EuroElso, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Maastricht Univ, Dept Cardiothorac Surg, Heart & Vasc Ctr, Cardiovasc Res Inst Maastricht CARIM,Med Hosp, Maastricht, Netherlands..
    Pressure and flow properties of cannulae for extracorporeal membrane oxygenation I: return (arterial) cannulae2019Ingår i: Perfusion, ISSN 0267-6591, E-ISSN 1477-111X, Vol. 34, s. 58-64Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Adequate extracorporeal membrane oxygenation support in the adult requires cannulae permitting blood flows up to 6-8 L/minute. In accordance with Poiseuille's law, flow is proportional to the fourth power of cannula inner diameter and inversely proportional to its length. Poiseuille's law can be applied to obtain the pressure drop of an incompressible, Newtonian fluid (such as water) flowing in a cylindrical tube. However, as blood is a pseudoplastic non-Newtonian fluid, the validity of Poiseuille's law is questionable for prediction of cannula properties in clinical practice. Pressure-flow charts with non-Newtonian fluids, such as blood, are typically not provided by the manufacturers. A standardized laboratory test of return (arterial) cannulae for extracorporeal membrane oxygenation was performed. The aim was to determine pressure-flow data with human whole blood in addition to manufacturers' water tests to facilitate an appropriate choice of cannula for the desired flow range. In total, 14 cannulae from three manufacturers were tested. Data concerning design, characteristics, and performance were graphically presented for each tested cannula. Measured blood flows were in most cases 3-21% lower than those provided by manufacturers. This was most pronounced in the narrow cannulae (15-17 Fr) where the reduction ranged from 27% to 40% at low flows and 5-15% in the upper flow range. These differences were less apparent with increasing cannula diameter. There was a marked disparity between manufacturers. Based on the measured results, testing of cannulae including whole blood flows in a standardized bench test would be recommended.

  • 7.
    Broman, Lars Mikael
    et al.
    Karolinska Univ Hosp, Dept Pediat Perioperat Med & Intens Care, ECMO Ctr Karolinska, S-17176 Stockholm, Sweden.;Karolinska Inst, Dept Physiol & Pharmacol, Stockholm, Sweden.;EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England..
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, BioMEx.
    Westlund, C. Jerker
    Karolinska Univ Hosp, Dept Pediat Perioperat Med & Intens Care, ECMO Ctr Karolinska, S-17176 Stockholm, Sweden..
    Gilbers, Martijn
    Maastricht Univ, Hosp Med, Cardiovasc Res Inst Maastricht CARIM, Heart & Vasc Ctr,Dept Cardiothorac Surg, Maastricht, Netherlands.;Maastricht Univ, Dept Physiol, Maastricht, Netherlands..
    da Camara, Luisa Perry
    Hosp Curry Cabral, Ctr Hosp Lisboa Cent, Lisbon, Portugal..
    Westin, Jan
    Karolinska Univ Hosp, Dept Med Technol, Stockholm, Sweden..
    Taccone, Fabio Silvio
    EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;ULB, Dept Intens Care, Hop Erasme, Brussels, Belgium..
    Malfertheiner, Maximilian Valentin
    EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Univ Med Ctr Regensburg, Dept Internal Med Cardiol & Pneumol 2, Regensburg, Germany..
    Di Nardo, Matteo
    EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Childrens Hosp Bambino Gesu, IRCCS, Pediat Intens Care Unit, Rome, Italy..
    Swol, Justyna
    EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Paracelsus Med Univ, Dept Pulmonol, Intens Care Med, Nurnberg, Germany..
    Vercaemst, Leen
    EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Univ Hosp Gasthuisberg, Dept Perfus, Louven, Belgium..
    Barrett, Nicholas A.
    EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Guys & St Thomas NHS Fdn Trust, Dept Crit Care, London, England.;Guys & St Thomas NHS Fdn Trust, Severe Resp Failure Serv, London, England..
    Pappalardo, Federico
    EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Univ Vita Salute San Raffaele, Hosp San Raffaele, Adv Heart Failure & Mech Circulatory Support Prog, Milan, Italy..
    Belohlavek, Jan
    EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Charles Univ Prague, Dept Med 2, Dept Cardiovasc Med, Gen Univ Hosp Prague, Prague, Czech Republic.;Charles Univ Prague, Fac Med 1, Prague, Czech Republic..
    Mueller, Thomas
    EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Univ Med Ctr Regensburg, Dept Internal Med Cardiol & Pneumol 2, Regensburg, Germany..
    Belliato, Mirko
    EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.;Fdn IRCCS Policlin San Matteo, UOC Anestesia & Rianimaz 1, Pavia, Italy..
    Lorusso, Roberto
    KTH, Skolan för teknikvetenskap (SCI), Centra, BioMEx. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. EuroELSO, Working Grp Innovat & Technol, Newcastle Upon Tyne, Tyne & Wear, England.
    Pressure and flow properties of cannulae for extracorporeal membrane oxygenation II: drainage (venous) cannulae2019Ingår i: Perfusion, ISSN 0267-6591, E-ISSN 1477-111X, Vol. 34, s. 65-73Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The use of extracorporeal life support devices such as extracorporeal membrane oxygenation in adults requires cannulation of the patient's vessels with comparatively large diameter cannulae to allow circulation of large volumes of blood (>5 L/min). The cannula diameter and length are the major determinants for extracorporeal membrane oxygenation flow. Manufacturing companies present pressure-flow charts for the cannulae; however, these tests are performed with water. Aims of this study were 1. to investigate the specified pressure-flow charts obtained when using human blood as the circulating medium and 2. to support extracorporeal membrane oxygenation providers with pressure-flow data for correct choice of the cannula to reach an optimal flow with optimal hydrodynamic performance. Eighteen extracorporeal membrane oxygenation drainage cannulae, donated by the manufacturers (n = 6), were studied in a centrifugal pump driven mock loop. Pressure-flow properties and cannula features were described. The results showed that when blood with a hematocrit of 27% was used, the drainage pressure was consistently higher for a given flow (range 10%-350%) than when water was used (data from each respective manufacturer's product information). It is concluded that the information provided by manufacturers in line with regulatory guidelines does not correspond to clinical performance and therefore may not provide the best guidance for clinicians.

  • 8.
    Fuchs, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, BioMEx. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Linköping Univ Hosp, Dept Radiol, SE-58185 Linköping, Sweden.
    Berg, Niclas
    KTH, Skolan för teknikvetenskap (SCI), Centra, BioMEx. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Centra, BioMEx.
    Stenosis Indicators Applied to Patient-Specific Renal Arteries without and with Stenosis2019Ingår i: FLUIDS, ISSN 2311-5521, Vol. 4, nr 1, artikel-id 26Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pulsatile flow in the abdominal aorta and the renal arteries of three patients was studied numerically. Two of the patients had renal artery stenosis. The aim of the study was to assess the use of four types of indicators for determining the risk of new stenosis after revascularization of the affected arteries. The four indicators considered include the time averaged wall shear stress (TAWSS), the oscillatory shear index (OSI), the relative reference time (RRT) and a power law model based in platelet activation modeling but applied to the endothelium, named endothelium activation indicator (EAI). The results show that the indicators can detect the existing stenosis but are less successful in the revascularized cases. The TAWSS and, more clearly, the EAI approach seem to be better in predicting the risk for stenosis relapse at the original location and close to the post-stenotic dilatation. The shortcomings of the respective indicators are discussed along with potential improvements to endothelial activation modeling and its use as an indicator for risks of restenosis.

  • 9.
    Fuchs, Gabriel
    et al.
    Sundsvall Reg Hosp, Sundsvall, Sweden..
    Berg, Niclas
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Broman, Mikael
    Karolinska Hosp, ECMO Ctr, Stockholm, Sweden..
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Blood clots in the ECMO-system - a theoretical platelet activation study2017Ingår i: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 61, nr 8, s. 964-965Artikel i tidskrift (Övrigt vetenskapligt)
  • 10.
    Fuchs, Gabriel
    et al.
    Dept. of Physiology and Pharmacology, Karolinska Institutet ; Department of Cardiology, Sundsvall’s Hospital.
    Berg, Niclas
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik.
    Broman, Mikael
    Dept. of Physiology and Pharmacology, Karolinska Institutet ; ECMO Centre Karolinska, Pediatric Perioperative Medicine and Intensive Care, Karolinska University Hospital.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Biomekanik.
    Modeling sensitivity and uncertainties in platelet activation models applied on centrifugal pumps for extracorporeal life support2019Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikel-id 8809Artikel i tidskrift (Refereegranskat)
  • 11.
    Håkansson, Karl
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fall, Andreas
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Yu, Sun
    DESY, Hamburg Germany.
    Krywka, Christina
    Institute of experimental and applied physics. Kiel Germany.
    Roth, Stephan
    DESY, Hamburg Germany.
    Santoro, Gonzalo
    DESY, Hamburg Germany.
    Kvick, Mathias
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Innventia AB, Stockholm Sweden.
    Hydrodynamic alignment and assembly of nanofibrils resulting in strong cellulose filaments2014Ingår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, s. 4018-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cellulose nanofibrils can be obtained from trees and have considerable potential as a building block for biobased materials. In order to achieve good properties of these materials, the nanostructure must be controlled. Here we present a process combining hydrodynamic alignment with a dispersion-gel transition that produces homogeneous and smooth filaments from a low-concentration dispersion of cellulose nanofibrils in water. The preferential fibril orientation along the filament direction can be controlled by the process parameters. The specific ultimate strength is considerably higher than previously reported filaments made of cellulose nanofibrils. The strength is even in line with the strongest cellulose pulp fibres extracted from wood with the same degree of fibril alignment. Successful nanoscale alignment before gelation demands a proper separation of the timescales involved. Somewhat surprisingly, the device must not be too small if this is to be achieved.

  • 12.
    Håkansson, Karl
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Kvick, Mathias
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Measurement of width and streakiness of particle streaks in turbulent flowsArtikel i tidskrift (Övrigt vetenskapligt)
  • 13.
    Håkansson, Karl
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fall, Andreas B.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Continuous assembly of aligned nanofibrils into a micro filamentManuskript (preprint) (Övrigt vetenskapligt)
  • 14.
    Håkansson, Karl
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Alignment of cellulose nanofibrils in a flow focusing device: mea-surements and calculations of flow and orientationManuskript (preprint) (Övrigt vetenskapligt)
  • 15.
    Håkansson, Karl
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Wågberg, Lars
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Orientation of nano-fibrillated cellulose in accelerated flowManuskript (preprint) (Övrigt vetenskapligt)
  • 16.
    Håkansson, Karl M. O.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Kvick, Mathias
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Measurement of width and intensity of particle streaks in turbulent flows2013Ingår i: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 54, nr 6, s. 1555-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fibre streaks are observed in experiments with fibre suspensions in a turbulent half-channel flow. The preferential concentration methods, most commonly used to quantify preferential particle concentration, are in one dimension found to be concentration dependent. Two different new streak quantification methods are evaluated, one based on Voronoi analysis and the other based on artificial particles with an assigned fixed width. The width of the particle streaks and a measure of the intensity of the streaks, i.e. streakiness, are sought. Both methods are based on the auto-correlation of a signal, generated by summing images in the direction of the streaks. Common for both methods is a severe concentration dependency, verified in experiments keeping the flow conditions constant while the (very dilute) concentration of fibres is altered. The fixed width method is shown to be the most suitable method, being more robust and less computationally expensive. By assuming the concentration dependence to be related to random noise, an expression is derived, which is shown to make the streak width and the streakiness independent of the concentration even at as low concentrations as 0.05 particles per pixel column in an image. The streakiness is obtained by applying an artificial particle width equal to 20 % of the streak width. This artificial particle width is in this study found to be large enough to smoothen the correlation without altering the streakiness nor the streak width. It is concluded that in order to make quantitative comparisons between different experiments or simulations, the evaluation has to be performed with care and be very well documented.

  • 17.
    Håkansson, Karl M. O.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl-Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Nanofibril Alignment in Flow Focusing: Measurements and Calculations2016Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 120, nr 27, s. 6674-6686Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Alignment of anisotropic supermolecular building blocks is crucial to control the properties of many novel materials. In this study, the alignment process of cellulose nanofibrils (CNFs) in a flow-focusing channel has been investigated using small-angle X-ray scattering (SAXS) and modeled using the Smoluchowski equation, which requires a known flow field as input. This flow field was investigated experimentally using microparticle-tracking velocimetry and by numerically applying the two-fluid level set method. A semidilute dispersion of CNFs was modeled as a continuous phase, with a higher viscosity as compared to that of water. Furthermore, implementation of the Smoluchowski equation also needed the rotational Brownian diffusion coefficient, which was experimentally determined in a shear viscosity measurement. The order of the nanofibrils was found to increase during extension in the flow-focusing channel, after which rotational diffusion acted on the orientation distribution, driving the orientation of the fibrils toward isotropy. The main features of the alignment and dealignment processes were well predicted by the numerical model, but the model overpredicted the alignment at higher rates of extension. The apparent rotational diffusion coefficient was seen to increase steeply as the degree of alignment increased. Thus, the combination of SAXS measurements and modeling provides the necessary framework for quantified studies of hydrodynamic alignment, followed by relaxation toward isotropy.

  • 18. Jadoon, A.
    et al.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Revstedt, J.
    Dynamic interaction of fixed dual spheres for several configurations and inflow conditions2010Ingår i: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 29, nr 1, s. 43-52Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The changes in force characteristics as well as the shedding patterns for various dual sphere configurations are studied. The Reynolds numbers considered are 300, 600 and two different inflow conditions are used: steady and pulsating. The sphere formations are defined by the separation distance D-0 between the spheres and the angle between the line connecting the centres of the spheres and the main flow direction, gamma. The position of one of the spheres is varied in the range 0 degrees-90 degrees using a 15 degrees increment. Two separation distances are studied; 1.5D and 3D. The method used for the simulations is the Volume of Solid (VOS) approach, a method based on Volume of Fluid (VOF). A major conclusion from this work is that the sphere interaction alters the wake dynamics by obstructing the vortex shedding (generating a steady wake or a wake with lower Strouhal number) and by changing the direction of the lift force so that it in most cases is directed in the plane containing the sphere centres. The results also show that changing the inflow condition gives the same relative change in drag and lift as for a single sphere. The drag is substantially reduced by placing the sphere downstream in a tandem arrangement and slightly increased in a side-by-side arrangement. However, the effect is decreased by increasing separation distance and increasing Reynolds number.

  • 19.
    Kekesi, Timea
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Drop deformation and breakup in flows with shear2016Ingår i: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 140, s. 319-329Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Volume of Fluid (VOF) method is applied to study the deformation and breakup of a single liquid drop in shear flows superimposed on uniform flow. The effect of shearing on the breakup mechanism is investigated as a function of the shear rate. Sequential images are compared for the parameter range studied; density ratios of liquid to gas of 20, 40, and 80, viscosity ratios in the range 0.5-50, Reynolds numbers between 20, a constant Weber number of 20, and the non-dimensional shear rate of the flow G = 0-2.1875. It is found that while shear breakup remains similar for all values of shear rate considered, other breakup modes observed for uniform flows are remarkably modified with increasing shear rate. The time required for breakup is significantly decreased in strong shear flows. A simple model predicting the breakup time as a function of the shear rate and the breakup time observed in uniform flows is suggested.

  • 20. Krochak, P.
    et al.
    Fasci, Giuseppe Carmine
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Norman, B.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Bridging chemical dosage, mixing quality, and variability in paper sheets2015Ingår i: TAPPI Journal, ISSN 0734-1415, Vol. 14, nr 5, s. 311-320Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the first part of this work, a series of paper production trials were performed on a forming experimental (FEX) pilot machine to investigate the distribution of additives in the final product. In these trials, a blue color was dosed into the stock before the headbox instead of a retention aid. Fine paper sheets were produced using twin-wire forming. Visual inspection of the sheets revealed surprisingly high levels of variability of the blue color. In the second part, the effect of different dosage nozzle configurations on downstream mixing quality of a single-component, polyacrylamide retention aid was studied using two-phase computational fluid dynamics. A non-Newtonian model for this phase was implemented using rheological parameters obtained through a combination of numerical and experimental analysis. Dosage was made into a turbulent pipe flow under typical industrial approach flow conditions. The effect of the number of dosage points, impingement angle, dosage location, and dosage speed on mixing uniformity was investigated qualitatively and quantitatively. Results from these studies indicate the existence of optimal dosage configurations and point toward strong coupling between chemical addition strategy, mixing quality, and chemical variability in final products. Application: Mills can gain valuable information, including dosage nozzle configuration and dosage conditions, for optimizing mixing of retention aids in the approach flow during paper production.

  • 21. Krochak, P.
    et al.
    Fasci, Giuseppe Carmini
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Biomekanik.
    Norman, B.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Biomekanik.
    Bridging chemical dosage, mixing quality and variability in paper sheets2013Ingår i: Pap. Conf. Trade Show, PaperCon, 2013, s. 1057-1069Konferensbidrag (Refereegranskat)
  • 22.
    Kvick, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Håkansson, Karl
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fibre orientation and fibre streaks in turbulent wall bounded flowManuskript (preprint) (Övrigt vetenskapligt)
  • 23.
    Kvick, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Håkansson, Karl
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Söderberg, Daniel
    Innventia.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Fibre streaks in wall turbulent flow2010Ingår i: 7th Int. Conference on Multiphase Flow, Tampa, Florida, USA, may 30 - June 4, 2010, ICMF , 2010Konferensbidrag (Refereegranskat)
  • 24.
    Kvick, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Söderberg, Daniel
    Effect of fibres on hydrodynami stability in a curved rotating channel2013Ingår i: ICMF2013, 2013, s. 674-Konferensbidrag (Refereegranskat)
  • 25.
    Kvick, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Söderberg, Daniel
    Effect of fibrils on curvature- and rotation-induced hydrodynamic stability2013Ingår i: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937, Vol. 224, nr 10, s. 2249-2261Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Flow of a suspension of water and nano-fibrillated cellulose (NFC) in a curved and rotating channel is studied experimentally and theoretically. The aim is to investigate how NFC affects the stability of the flow. This flow is subject to a centrifugal instability creating counter-rotating vortices in the flow direction. These rolls can be both stabilised and destabilised by system rotation, depending on direction and velocity of the rotation. Flow visualisation images with pure water and an NFC/water suspension are categorised, and stability maps are constructed. A linear stability analysis is performed, and the effect of fibrils is taken into account assuming straight fibrils and constant orientation distributions, i.e., without time-dependent flow-orientation coupling. The results show that NFC has a less stabilising effect on the primary flow instability than indicated from the increase in viscosity measured by a rotary viscometer, but more than predicted from the linear stability analysis. Several unknown parameters (the most prominent being fibril aspect ratio and the interaction parameter in the rotary diffusion) appear in the analysis.

  • 26.
    Kvick, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Effects of nano-fibrillated cellulose on curvature- and rotation-induced instabilities in channel flowManuskript (preprint) (Övrigt vetenskapligt)
  • 27.
    Kvick, Mathias
    et al.
    KTH. KTH Mech, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH Mech, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH Mech, Linne FLOW Ctr, S-10044 Stockholm, Sweden..
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. Innventia AB, S-11486 Stockholm, Sweden..
    Erratum to: Effect of fibrils on curvature-and rotation-induced hydrodynamic stability2015Ingår i: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937, Vol. 226, nr 4, s. 1319-1321Artikel i tidskrift (Refereegranskat)
  • 28.
    Kvick, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Stability of the flow in a flow-focusing deviceManuskript (preprint) (Övrigt vetenskapligt)
  • 29.
    Kékesi, Timea
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Altimira, Mireia
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Interaction between two deforming liquid drops in tandem and various off-axis arrangements subject to uniform flow2019Ingår i: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, s. 193-218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Volume of Fluid (VOF) method is applied to study the interaction between two liquid drops with the same initial diameter in uniform flow. Various arrangements of the drops are studied, based on two parameters, namely the initial separation distance and the angle between the line connecting the centres of the drops and the free-stream direction. Initial separation distances of 1.5–5 drop diameters, and angles between β=0 ∘ and 90° are considered. Simulations for a Weber number of We=20, two Reynolds numbers Re=20 and 50, and density and viscosity ratios in the range ρ * =20–80 and μ * =0.5–50 are performed. The movement of the secondary drop with respect to the primary drop, and estimates on the time required for the breakup of the secondary drop as compared to those observed for single drops are evaluated. It is found that the drops collide only in cases corresponding to the shortest initial displacements, while in others they deform and break up independently, similarly or identically to single drops. The same behaviour is reflected in the time required for breakup. Cases where the drops behave independently show breakup times close to those observed for single drops.

  • 30.
    Kékesi, Timea
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Corrigendum to: "Drop deformation and breakup". Int. J. Multiphase Flow, 66, (2014) 1-102016Ingår i: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533Artikel i tidskrift (Refereegranskat)
  • 31.
    Kékesi, Timea
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Drop deformation and breakup2014Ingår i: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 66, s. 1-10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Volume of Fluid (VOF) method is applied to investigate the deformation and breakup of an initially spherical drop in the bag- and shear breakup regimes, induced by steady disturbances. The onset of breakup is sought by studying steady-shape deformations while increasing the Weber number until breakup occurs. A parameter study is carried out applying different material properties and a wide range of drop Reynolds numbers in the steady wake regime. Density ratios of liquid to gas of 20, 40, and 80, viscosity ratios in the range 0.5-50, and Reynolds numbers between 20 and 200 are investigated for a constant Weber number of 20. The critical Weber number is found to be 12, in agreement with observations of earlier studies. For Weber number of 20 varying density, viscosity ratios and Reynolds numbers, interesting mixed breakup modes are discovered. Moreover, a new regime map including all modes observed is presented. A criterion for the transition between bag-and shear breakup is defined relating the competing inertial and shear forces appearing in the flow. Furthermore, results on breakup times and the time history of the drag coefficient are presented; the latter is concluded to be a potential parameter to indicate the occurrence of breakup. (C) 2014 Elsevier Ltd. All rights reserved.

  • 32.
    Kékesi, Tímea
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Altimira, Mireia
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Interaction between two deforming liquid drops in tandem and various off-axis arrangements subject to uniform flowManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    A Volume of Fluid (VOF) method is applied to study the interaction between two liquid drops with the same initial diameter in uniform flow. Various arrangements of the drops are studied, based on two parameters, namely the initial separation distance and the angle between the line connecting the centres of the drops and the free-stream direction. Specifically, initial separation distances of l = 1.5 − 5D drop diamters, and angles between β = 0◦ − 90◦ are considered. Simulations for a Weber number of W e = 20, two Reynolds numbers Re = 20 and 50, and density and viscosity ratios in the range ρ∗ = 20 − 80 and μ∗ = 0.5 − 50 are performed. The movement of the secondary drop with respect to the primary drop, and the time required for the breakup of the secondary drop as compared to those observed for single drops are evaluated. It is found that the drops collide only in cases corresponding to the shortest initial displacements, while in others they deform and break up independently, similar or identical to single drops. The same behaviour is reflected in the time required for breakup. Cases where the drops behave independently show breakup times close to those observed for single drops.

  • 33.
    Lacagnina, Giovanni
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. Institute of Sound and Vibration Research (ISVR), University of Southampton, United Kingdom.
    Szász, Robert-Zoltán
    Department of Energy Sciences, LTH Faculty of Engineering, Lund University.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Experimental study on the forcing design for an intermittent injection2018Ingår i: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 59, nr 8, artikel-id 123Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we consider the effects of acceleration and deceleration on the forcing of an intermittent jet. This experimental study specifically focuses on the effect of the acceleration and deceleration on the mixing of an intermittent jet with the ambient fluid and on the growth of disturbances that may lead to turbulence. The influence of different injection strategies has been evaluated. The results show that the deceleration phase may be able to contribute significantly to enhance the mixing of the jet with the ambient fluid. This effect is manifested primarily around the tail of the jet, towards the end of injection. The acceleration phase on the other hand has mainly impact at the leading part of the jet, where the leading part of the jet forms a mushroom shaped structure with minor mixing effect.

  • 34.
    Mylavarapu, Goutham
    et al.
    Aerospace Engineering, University of Cincinnati.
    Mihaescu, Mihai
    Aerospace Engineering, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Murugappan, Shanmugam
    Otolargyngology, Head and Neck Surgery, University of Cincinnati-Medical Center.
    Prahl Wittberg, Lisa
    Dept. Energy Sciences, Division of Fluid Mechanics, Lund University.
    Fuchs, Laszlo
    Dept. Energy Sciences, Division of Fluid Mechanics, Lund University.
    Papatziamos, Georgios
    Karolinska Hospital Solna.
    Importance of paranasal sinuses in computational modeling of nasal airflow2009Ingår i: 47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, AIAA , 2009, s. 2009-0772-Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper investigates the importance of including paranasal sinuses in the computational modeling of the nasal airflow. Three dimensional models of human nasal airway with and without including paranasal sinuses were reconstructed from Computed Tomography (CT) axial images of a subject with healthy nasal airway. The reconstruction process was performed using MIMICS® software program. The airway volume was discretized using TGRID® mesh generator. Steady Reynolds-Averaged Navier-Stokes (RANS) simulations were carried in both inspiratory and expiratory phases of respiratory cycle at a peak flow rate of 15 L/min in FLUENT®. The results show that the left and right nasal resistances change with less than 11% when paranasal sinuses are included in the computational model of the nasal airway. The flow into the sinuses is characterized by very low velocities during both inspiration and expiration conditions. The velocity distributions in the main nasal passage show small change predominantly in regions closer to the paranasal sinuses when compared to the model where sinuses were not included.

  • 35.
    Nygård, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Altimira, M.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Analysis of vortical structures in intermittent jets2016Ingår i: Springer Proceedings in Physics, Springer Science+Business Media B.V., 2016, s. 3-10Konferensbidrag (Refereegranskat)
    Abstract [en]

    The manipulation of jets has since long been subject to research, due to the wide range of industrial applications in which they are used. A vast number of numerical and experimental studies concerning the physics of the breakup process of continuous jets have been published. Improvements in mixing and ambient gas entrainment have been reported experimentally when using intermittent injection, although the responsible mechanisms have not yet been completely revealed. This work presents a systematic analysis of the mechanisms of jet breakup and mixing with the surrounding fluid and its relation to vorticity generation and transport. Comparisons aremade between the redistribution of vorticity and the engulfment of ambient fluid into the core region for different injection strategies. © Springer International Publishing Switzerland 2016.

  • 36.
    Nygård, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Altimira, Mireia
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Disintegration Mechanisms of Intermittent Liquid Jets2016Ingår i: SAE International Journal of Fuels and Lubricants, ISSN 1946-3952, E-ISSN 1946-3960, Vol. 9, nr 1, s. 91-99Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It has been observed that intermittent injection leads to improved spray characteristics in terms of mixing and gas entrainment. Although some experimental work has been carried out in the past, the disintegration mechanisms that govern the breakup of intermittent jets remain unknown. In this paper we have carried out a systematic numerical analysis of the breakup of pulsated jets under different injection conditions. More specifically, the duty cycle (share of active injection during one cycle) is varied, while the total cycle time is kept constant. The advection of the liquid phase is handled through the Volume of Fluid approach and, in order to provide an accurate, yet computationally acceptable, resolution of the turbulent structures, the implicit Large Eddy Simulation has been adopted. The results show that the primary disintegration results from a combination of stretching, collision and aerodynamic interaction effects. Moreover, there exists a strong coupling between stretching and collision as stretching makes the pulse thinner prior to the contact between pulses. In this work, the purpose is to study the collision contribution to breakup in terms of the near nozzle pulse disintegration rate. When approaching the low duty cycle limit, this effect is significant because of the lower liquid volume of the pulse. In contrast, for a high duty cycle, the stretching effect is limited and a wide tail region remains as an obstruction for following pulses. However, the integral momentum of the pulse is maintained to a larger degree that has an adverse effect on the outcome of the collision event.

  • 37.
    Nygård, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Altimira, Mireia
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Quantifying primary breakup in pulsating liquid2014Ingår i: / [ed] A. Eriksson, A. Kulachenko, M. Mihaescu and G. Tibert, 2014Konferensbidrag (Refereegranskat)
  • 38.
    Nygård, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Altimira, Mireia
    Lund University.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Interaction between liquid pulses during intermittent injection2014Ingår i: Proceedings of the 26th ILASS-Europe 2014, 2014Konferensbidrag (Refereegranskat)
  • 39.
    Prahl Wittberg, Lisa
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Björkman, M.
    Khokhar, Gohar
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Mohlin, U. -B
    Dahlkild, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Flow conditions in the grooves of a Low-Consistency refiner2012Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, nr 2, s. 173-183Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The flow pattern in the grooves plays a major role for the homogeneity of refining as well as for the transfer and loading of fiber flocs in refining position on the bar edges. However, it is an area where very little information is available. In the present study, flow conditions in the grooves in a Low-Consistency (LC) - disc refiner were studied both experimentally and numerically. The experimental study involved high-speed imaging through a 3 cm peephole into a commercial refiner. The Computational Fluid Dynamics (CFD) simulation focused on the flow condition in a radial groove, considering both Newtonian and non-Newtonian flows. Flow conditions for stator and rotor grooves were modeled along the groove at different angular speeds and pressure differences over the refiner. Both the experimental and the modeling results show a dual flow pattern in the grooves; a rotational/spiral movement at the top of the groove and a flow in the direction of the groove at the bottom, which to the authors knowledge has not been reported in literature. The strong vortical motion at the top of the grooves observed both for the rotor and the stator are believed to be important for placing the fibers onto the bar edges and to induce shear forces in such a way that the fibers get treated. Moreover, a large sensitivity to suspension properties in terms of the development of flow pattern was detected.

  • 40. Prahl Wittberg, Lisa
    et al.
    Hoelzer, A.
    Arlov, D.
    Revstedt, J.
    Sommerfeld, M.
    Fuchs, Laszlo
    On the interaction between two fixed spherical particles2007Ingår i: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 33, nr 7, s. 707-725Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The variation of the drag (CD) and lift coefficients (CL) of two fixed solid spherical particles placed at different positions relative each other is studied. Simulations are carried out for particle Reynolds numbers of 50, 100 and 200 and the particle position is defined by the angle between the line connecting the centers of the particles and the free-stream direction (a) and the separation distance (do) between the particles. The flow around the particles is simulated using two different methods; the Lattice Boltzmann Method (LBM), using two different computational codes, and a conventional finite difference approach, where the Volume of Solid Method (VOS) is used to represent the particles. Comparisons with available numerical and experimental data show that both methods can be used to accurately resolve the flow field around particles and calculate the forces the particles are subjected to. Independent of the Reynolds number, the largest change in drag, as compared to the single particle case, occurs for particles placed in tandem formation. Compared to a single particle, the drag reduction for the secondary particle in tandem arrangement is as high as 60%, 70% and 80% for Re = 50, 100 and 200, respectively. The development of the recirculation zone is found to have a significant influence on the drag force. Depending on the flow Situation in-between the particles for various particle arrangements, attraction and repulsion forces are detected due to low and high pressure regions, respectively. The results show that the inter-particle forces are not negligible even under very dilute conditions.

  • 41.
    Prahl Wittberg, Lisa
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Biomekanik. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Jadoon, A.
    Revstedt, J.
    Interaction between two spheres placed in tandem arrangement in steady and pulsating flow2009Ingår i: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 35, nr 10, s. 963-969Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interaction among two spheres in tandem formation are studied for a Reynolds number of 300 using both steady and pulsating inflow conditions. The purpose is to further investigate the force characteristics as well as the shedding patterns of the two spheres as the separation distance is changed from 1.5 to 12. sphere diameters. The method used for the simulations is the volume of solid (VOS) method, an approach based on the volume of fluid (VOF) method. Comparisons with other computational methods have shown VOS to accurately resolve the flow field around solid spheres. The results show that the separation distance plays a significant role in changing the flow patterns and shedding frequencies at moderate separation distances, whereas effect on drag is observed even at a separation distance of 12 diameters.

  • 42.
    Prahl Wittberg, Lisa
    et al.
    Lunds Universitet, LTH, Div. Fluid mechanics.
    Revstedt, Johan
    Lunds Universitet, LTH, Div. Fluid mechanics.
    Fuchs, Laszlo
    Lunds Universitet, LTH, Div. Fluid mechanics.
    A study of the dynamics of dual-particles settling close to a vertical wall2005Ingår i: 4th interntional Conference on Turbulence and Shear Flow Phenomena, Williamsbrug, Viriginia, USA, June 27-29, 2005, 2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    Simulations of single and multiple spherical particles settling under gravity in the presence of a vertical wall are performed. In this study, the Reynolds number based on a characteristic velocity set to unity and the diameter of the sphere is varied in the range from 1 to 1000 and the density ratio in the range from 1.5 to 8. Interaction between particles as well as with the wall is investigated. The particles are modeled by using the Volume of Solid (VOS) approach, a method based on the Volume of Fluid (VOF) approach.The simulations showed that the motion of both single and dual spheres falling side by side is affected by the wall. Also, a dominant frequency for the oscillatory movements perpendicular to the wall was detected.

  • 43.
    Prahl Wittberg, Lisa
    et al.
    Lunds Universitet, LTH, Avd. för Strömningsmekanik.
    Revstedt, Johan
    Lunds Universitet, LTH, Div. Fluid mechanics.
    Fuchs, Laszlo
    Lunds Universitet, LTH, Div. Fluid mechanics.
    Interaction among droplets in a uniform flow at intermediate Reynolds numbers2006Ingår i: 44th AIAA Aerospace and Science Meeting, Reno, Nevada, USA, Jan 9-12, 2006, American Institute of Aeronautics and Astronautics , 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    Simulations of single and dual droplets in a uniform flow for Reynolds numbers 100and Weber numbers of 0.1 and 1.0 are performed on a Cartesian grid using the Volume ofFluid method. The simulations are carried out to provide a detailed study of the interactionbetween droplets. Thus, the main focus is to investigate the forces a droplet is subjectedto as its position is changed in relation to a reference droplet. The results are comparedto simulations for solid particles using the Volume of Solid, a method based on the Volumeof Fluid approach. The results show the importance of accounting to the full interactionamong the droplets. Such interaction has to be included even for rather diluted two-phasesystems. The large number of calculations results in a data-base that can be used as alook-up table for accounting for the inter-droplet interaction (i.e. effects on lift- and dragcoefficients)in the frame-work of Lagrangian particle tracking approach. Additionally, wedo take into account also droplet deformation, which has significant effect for droplet inmany engineering applications.

  • 44.
    Prahl Wittberg, Lisa
    et al.
    Lunds Universitet, LTH, Div. Fluid mechanics.
    Revstedt, Johan
    Lunds Universitet, LTH, Div. Fluid mechanics.
    Fuchs, Laszlo
    Lunds Universitet, LTH, Div. Fluid mechanics.
    Sphere wake dynamics2008Ingår i: Int. Conf. on Jets, Wakes and Separated Flows, Berlin, Germany, Sept 16-19, 2008, Technical University of Berlin , 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Understanding the flow behavior around spheres is of great importance when it comes to improving the efficiency of any industrial application involving multiphase flow systems. The purpose with this study is to continue the work and further investigate the wake dynamics behind interacting spheres under steady and periodic free-stream conditions. Both single and dual sphere configurations are considered, focusing on Reynolds number at values around which, flow transitions have been found to occur.

    The results shows that "lock on" to the free-stream flow frequency is more likely to occur for free-stream frequencies greater than the frequency associated with the natural vortex shedding. The appearance of a low frequeny mode can often be related to a swirling motion of the wake. Also, the vortex shedding for tandem config-urations is delayed at short inter-particle distances and the vorticle strucctures in the flow field of two spheres in tandem are different as compared to those observed for a single sphere

  • 45.
    Prahl Wittberg, Lisa
    et al.
    Lunds Universitet, LTH, Div. Fluid mechanics.
    Revstedt, Johan
    Lunds Universitet, LTH, Div. Fluid mechanics.
    Fuchs, Laszlo
    Lunds Universitet, LTH, Div. Fluid mechanics.
    The interaction among two fixed spherical particles in an oscillatory flow2007Ingår i: 5th Conference on Bluff Body Wakes and Vortex-Induced Vibrations, Bahia, Brazil, Dec 12 -15, 2007, 2007Konferensbidrag (Refereegranskat)
  • 46.
    Prahl Wittberg, Lisa
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Revstedt, Johan
    Lunds Universitet, LTH, Div. Fluid mechanics.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Hydrodynamic interaction among multiple spherical particles2010Ingår i: 7 Int. Conference on Multiphase Flow, Tampa, Florida, USA, May 30 - June 4, 2010, 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Multiple sphere formations are studied for Reynolds numbers of 100 − 300 in order to better understand the hydrodyanmicalinteraction among spheres. Spheres placed in tandem, diagonal as well as cluster formations including3–5 spheres are investigated using a conventional finite difference method where the Volume of Solid (VOS) methodis used to represent the spherical particles. The results show that, independent of sphere formation, an overall trend isthat the front spheres are the least affected by the inclusion of additional spheres in the formation. Although spherecharacteristics depending on position within a formation is found, the behavior of the trailing spheres changes withformation type, number of spheres, separation distances and Reynolds numbers.

  • 47.
    Prahl Wittberg, Lisa
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    van Wyk, Stevin
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Gutmark, E.
    Backeljauw, P.
    Gutmark-Little, I.
    Effects of aortic irregularities on blood flow2016Ingår i: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 15, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Anatomic aortic anomalies are seen in many medical conditions and are known to cause disturbances in blood flow. Turner syndrome (TS) is a genetic disorder occurring only in females where cardiovascular anomalies, particularly of the aorta, are frequently encountered. In this study, numerical simulations are applied to investigate the flow characteristics in four TS patient- related aortic arches (a normal geometry, dilatation, coarctation and elongation of the transverse aorta). The Quemada viscosity model was applied to account for the non-Newtonian behavior of blood. The blood is treated as a mixture consisting of water and red blood cells (RBC) where the RBCs are modeled as a convected scalar. The results show clear geometry effects where the flow structures and RBC distribution are significantly different between the aortas. Transitional flow is observed as a jet is formed due to a constriction in the descending aorta for the coarctation case. RBC dilution is found to vary between the aortas, influencing the WSS. Moreover, the local variations in RBC volume fraction may induce large viscosity variations, stressing the importance of accounting for the non-Newtonian effects.

  • 48.
    Prahl-Wittberg, Lisa
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Biomekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    van Wyk, Stevin
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Biomekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Backeljauw, Philippe
    Cincinnati Children's Hospital.
    Gutmark-Little, Iris
    Cincinnati Children's Hospital.
    The Impact of Aortic Arch Geometry on Flow Characteristics2013Ingår i: / [ed] AIAA, AIAA, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Cardiovascular defects characterized by geometrical anomalies of the aorta and its eecton the blood ow is the focus of this study. Not only are the local ow characteristicsgeometry dependent, but they are also directly connected to the rheological properties ofblood. Flow characteristics such as wall shear stress are often postulated to play a centralrole in the development of vascular disease.In this study, blood is considered to be a non-Newtonian uid and modeled via theQuemada model, an empirical model that is valid for dierent red blood cell loading.Three patient-specic geometries of the aortic arch are investigated numerically. Thethree geometries investigated in this study all display malformations that are prevalent inpatients having the genetic disorder Turner syndrome. The results show a highly complexow with regions of secondary ow that are enhanced in two of the three aortas. Moreover,blood ow is clearly diverted due to the malformations, moving to a larger extent throughthe branches of the arch instead of through the descending aorta. The geometry havingan elongated transverse aorta is found to be subjected to larger areas of highly oscillatorylow wall shear stress.

  • 49. Söder, M.
    et al.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Lindgren, B.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Effect of Swirl/Tumble (Tilt) Angle on Flow Homogeneity, Turbulence and Mixing Properties2014Ingår i: SAE technical paper series, ISSN 0148-7191, Vol. 2014-OctoberArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, the effect of swirl to tumble ratio on homogeneity, turbulence and mixing in a generic heavy duty Diesel engine during compression, is investigated using Large-Eddy Simulations. The main conclusion is that the relative importance of dilatation (relative volume change) increases whereas the effect of tumble breakdown decreases with the swirl to tumble ratio. In detail, we show that an increase in tumble raises the peak turbulence level and shifts the peak to earlier crank angles, which in turn leads to higher dissipation. Moreover, maximum turbulence level at top dead center is obtained for a combination of swirl and tumble rather than for pure tumble. Furthermore, it is observed that the peak turbulent kinetic energy displays levels three times greater than the initial kinetic energy of the tumble motion. Thus, energy is added to the flow (turbulence) by the piston through generation of vorticity by vorticity-dilatation interaction. Also, the intermediate swirl/tumble ratios are found to introduce large non-uniformity in the flow field, leading to a non-solid body like rotation. Swirl/tumble (tilt) angles larger than 19°are necessary for complete mixing of the gas within the engine cylinder. Taken together, the combined effect of a combination of swirl and tumble turbulence during compression is investigated. This knowledge is important both for engine development as well as more theoretical aspects regarding the breakdown of large scale structures in an engine.

  • 50.
    Söder, Martin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. Scania CV, Sweden.
    Lindgren, Björn
    Scania CV, Sweden.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Laszlo, Fuchs
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Effect of swirl/tumble (Tilt) angle on flow homogeneity, turbulence and mixing propertiesManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    In this work, the effect of swirl to tumble ratio on homogeneity, turbulence and mixing in a generic heavy duty Diesel engine during compression, is investigated using Large-Eddy Simulations. The main conclusion is that the relative importance of dilatation (relative volume change) increases whereas the effect of tumble breakdown decreases with the swirl to tumble ratio.In detail, we show that an increase in tumble raises the peak turbulence level and shifts the peak to earlier crank angles, which in turn leads to higher dissipation. Moreover, maximum turbulence level at top dead center is obtained for a combination of swirl and tumble rather than for pure tumble. Furthermore, it is observed that the peak turbulent kinetic energy displays levels three times greater than the initial kinetic energy of the tumble motion. Thus, energy is added to the flow (turbulence) by the piston through generation of vorticity by vorticity-dilatation interaction. Also, the intermediate swirl/tumble ratios are found to introduce large non-uniformity in the flow field, leading to a non-solid body like rotation. Swirl/tumble (tilt) angles larger than 19 deg are necessary for complete mixing of the gas within the engine cylinder. Taken together, the combined effect of a combination of swirl and tumble turbulence during compression is investigated. This knowledge is important both for engine development as well as more theoretical aspects regarding the breakdown of large scale structures in an engine.

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