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  • 1. Altimira, M.
    et al.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Corrigendum to Numerical investigation of throttle flow under cavitating conditions (International Journal of Multiphase Flow 75 (2015) 124–136) (S0301932215001238) (10.1016/j.ijmultiphaseflow.2015.05.006))2017In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 93, p. 216-217Article in journal (Refereed)
    Abstract [en]

    The authors regret that the figures that were included in the final version of their paper were incorrect. Corrected Figures 3, 4, 5, and 6 are included here. The authors would like to apologise for any inconvenience caused. 

  • 2.
    Berg, Niclas
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics, Biomechanics.
    Blood flow simulations of the renal arteries - effect of segmentation and stenosis removalIn: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987Article in journal (Refereed)
    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, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, BioMEx.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Centres, BioMEx. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, BioMEx. KTH Mech, Linne FLOW Ctr, BioMEx, SE-10044 Stockholm, Sweden..
    Blood Flow Simulations of the Renal Arteries - Effect of Segmentation and Stenosis Removal2019In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 102, no 1, p. 27-41Article in journal (Refereed)
    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, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics, Biomechanics.
    Flow characteristics and coherent structures in a centrifugal blood pump2019In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 102, no 2, p. 469-483Article in journal (Refereed)
    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, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Mechanics, Biomechanics.
    Influence of red blood cell polydispersity on blood rheology and platelet marginationManuscript (preprint) (Other academic)
  • 6. Grosshans, H.
    et al.
    Movaghar, A.
    Cao, L.
    Oevermann, M.
    Szasz, R. -Z
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Sensitivity of VOF simulations of the liquid jet breakup to physical and numerical parameters2016In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 136, p. 312-323Article in journal (Refereed)
    Abstract [en]

    In this paper the characteristics of the primary breakup of a liquid jet is analyzed numerically. We applied the Volumes of Fluids (VOF) approach utilizing the Direction Averaged Curvature (DAC) model, to estimate the interface curvature, and the Direction Averaged Normal (DAN) model, to propagate the interface. While being used for the first time to predict liquid atomization, this methodology showed a high accuracy. The influence of varying the fluid properties, namely liquid-gas density and viscosity ratio, and injection conditions is discussed related to the required grid resolution. Resulting droplet sizes are compared to distributions obtained through the One-Dimensional Turbulence (ODT) model.

  • 7.
    Hodzic, Erdzan
    et al.
    Queens Univ Belfast, Sch Mech & Aerosp Engn, Belfast, Antrim, North Ireland.;Lund Univ, Dept Energy Sci, Lund, Sweden..
    Jangi, Mehdi
    Univ Birmingham, Dept Mech Engn, Birmingham, W Midlands, England..
    Szasz, Robert-Zoltan
    Lund Univ, Dept Energy Sci, Lund, Sweden..
    Duwig, Christophe
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Geron, Marco
    Queens Univ Belfast, Sch Mech & Aerosp Engn, Belfast, Antrim, North Ireland..
    Early, Juliana
    Queens Univ Belfast, Sch Mech & Aerosp Engn, Belfast, Antrim, North Ireland..
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Bai, Xue-Song
    Lund Univ, Dept Energy Sci, Lund, Sweden..
    Large Eddy Simulation of Bluff-Body Flame Approaching Blow-Off: A Sensitivity Study2019In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 191, no 10, p. 1815-1842Article in journal (Refereed)
    Abstract [en]

    As almost all combustion processes of practical interest take place in the presence of turbulence, the development of the increasingly refined turbulence-chemistry interaction (TCI) models has led to highly sophisticated approaches. Nearly all of the studies comparing different models focus on stable premixed/non-premixed flame configurations. In this work, the focus is on well-documented, lean premixed bluff-body stabilized flames approaching blow-off and on the blow-off sequence itself. Large Eddy Simulations (LES) have been used to capture the time-dependent, three-dimensional flow-field using Transported Probability Density Function (TPDF), Partially Stirred Reactor Model (PaSR), and Implicit LES (ILES) models. Furthermore, the influence of finite-rate chemistry and different chemical mechanisms is evaluated to determine the limitation and capability of the different TCI approaches for modeling flames just prior to and during the transient blow-off process. While the average flow-fields do not reveal any significant differences between modeling approaches, detailed analysis of the flame reveals that there are differences in the predicted flame thickness and composition. The ability of the considered TCI models to predict local as well as full-flame extinction during the blow-off is investigated as well. It is demonstrated that such a blow-off sequence is not always governed by complex chemistry.

  • 8.
    Lacagnina, Giovanni
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. 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, School of Engineering Sciences (SCI), Mechanics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Experimental study on the forcing design for an intermittent injection2018In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 59, no 8, article id 123Article in journal (Refereed)
    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.

  • 9.
    Mihaescu, Mihai
    et al.
    Energy Sciences, Lund University.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Sound Generated by an Unsteady Flow Field, Using a Hybrid Method2004In: Modelling Fluid Flow: The State of the Art, Springer-Verlag , 2004, 1, , p. 169-178p. 169-178Chapter in book (Refereed)
    Abstract [en]

    The compressible Navier-Stokes equations describe both flow field as well as sound generation. The classical acoustic theory uses the hypothesis that the part of the flow field, which is the source of the acoustic field, has distinct scales so that the acoustic waves do not interfere with the flow. Thus, the velocity vector, the pressure and the density are split into semi-compressible components and an inviscid, irrotational acoustical components. The paper includes the details of the coupling between the turbulent flow (based on Large Eddy Simulation) and the acoustical part (based on Lighthill's acoustic analogy). The approach is applied to the acoustics of a non-isothermal jet.

  • 10.
    Nygård, Alexander
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Altimira, M.
    Semlitsch, Bernhard
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Analysis of vortical structures in intermittent jets2016In: Springer Proceedings in Physics, Springer Science+Business Media B.V., 2016, p. 3-10Conference paper (Refereed)
    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.

  • 11. Szasz, R.
    et al.
    Subash, A. A.
    Lantz, A.
    Collin, R.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. Lund University, Sweden.
    Gutmark, E.
    Hysteretic Dynamics of Flashback in a Low-Swirl Stabilized Combustor2017In: Combustion Science and Technology, ISSN 0010-2202, E-ISSN 1563-521X, Vol. 189, no 2, p. 266-289Article in journal (Refereed)
    Abstract [en]

    The hysteretic behavior of flashback (FB) and flash forward (FF) in methane and natural gas flames, stabilized by a low swirl fuel injector, is investigated using high speed OH* chemiluminescence and particle image velocimetry. Due to the lack of vortex breakdown, the two mechanisms discussed are boundary layer and turbulence induced FB. Two hysteresis cycles were identified, one when FB is induced by increasing the equivalence ratio starting from lean conditions, and the other by decreasing the equivalence ratio starting from rich conditions. Impact of relevant parameters including Reynolds number (Re), equivalence ratio, fuel type, combustion chamber geometry, preheating, and mixing tube protrusions are investigated. As Re is increased, the equivalence ratio at which both rich and lean flashbacks occur approaches stoichiometric conditions. However, the range of the hysteresis cycle between FB and FF is independent on Re. The transition processes during FB and FF are quite variable and their duration is independent on Re. The mean duration of FB transition initiated from lean conditions is nearly twice longer than the rich branch and also longer than both the lean and rich FF. The geometry of the combustion chamber affected neither FB nor FF. However, preheating increased the equivalence ratio at which FB occurred but did not affect FF. Also, FB had significant effect on the mean flow field.

  • 12. Szász, R. -Z
    et al.
    Subash, A. A.
    Lantz, A.
    Collin, R.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Gutmark, E. J.
    Algorithm for automatic quantification of flashback and flash forward events from high-speed chemiluminescence recordings2016In: Springer Proceedings in Physics, Springer Science+Business Media B.V., 2016, p. 519-526Conference paper (Refereed)
    Abstract [en]

    Three methods are employed to identify and quantify flashback and flash forward events based on chemiluminescence recordings of swirling flames. The approaches differ in the procedure to determine the instantaneous flame position. The results revealed that the most robust method is to determine a threshold relative to the instantaneous maximum intensity. Analysis of the complete dataset indicated that flashback events are significantly slower than flash forward events.

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