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  • 1. Abbasi Hoseini, A.
    et al.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Andersson, H. I.
    Finite-length effects on dynamical behavior of rod-like particles in wall-bounded turbulent flow2015In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 76, p. 13-21Article in journal (Refereed)
    Abstract [en]

    Combined Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) measurements have been performed in dilute suspensions of rod-like particles in wall turbulence. PIV results for the turbulence field in the water table flow apparatus compared favorably with data from Direct Numerical Simulations (DNS) of channel flow turbulence and the universality of near-wall turbulence justified comparisons with DNS of fiber-laden channel flow. In order to examine any shape effects on the dynamical behavior of elongated particles in wall-bounded turbulent flow, fibers with three different lengths but the same diameter were used. In the logarithmic part of the wall-layer, the translational fiber velocity was practically unaffected by the fiber length l. In the buffer layer, however, the fiber dynamics turned out to be severely constrained by the distance z to the wall. The short fibers accumulated preferentially in low-speed areas and adhered to the local fluid speed. The longer fibers (l/z > 1) exhibited a bi-modal probability distribution for the fiber velocity, which reflected an almost equal likelihood for a long fiber to reside in an ejection or in a sweep. It was also observed that in the buffer region, high-speed long fibers were almost randomly oriented whereas for all size cases the slowly moving fibers preferentially oriented in the streamwise direction. These phenomena have not been observed in DNS studies of fiber suspension flows and suggested l/z to be an essential parameter in a new generation of wall-collision models to be used in numerical studies.

  • 2. 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. 

  • 3. Altimira, M.
    et al.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Numerical investigation of throttle flow under cavitating conditions2015In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 75, p. 124-136Article in journal (Refereed)
    Abstract [en]

    The present paper shows the importance of the resolution of large unsteady flow structures in numerical simulations of cavitating flows. Three-dimensional simulations of the flow through a throttle geometry representative for fuel injectors have been performed to characterise the inception and development of cavitation, adopting the implicit Large Eddy Simulation approach. The two-phase flow has been handled by the Volume of Fluid method; whilst the simplified Rayleigh equation has been adopted to handle bubble dynamics. The mathematical model has been solved in the open source C++ toolbox OpenFOAM 2.0.1. Results obtained with the mathematical model are compared with those from RANS-based simulations and validated against experimental measurements. The performed Large Eddy Simulations not only are able to reproduce vortex cavitation, but also give further insight into the complex interaction between cavitation and turbulence through the assessment of the different terms of the vorticity equation.

  • 4.
    Anglart, Henryk
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
    Persson, Per
    Experimental investigation of post-dryout heat transfer in annulus with spacers2007In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 33, no 8, p. 809-821Article in journal (Refereed)
    Abstract [en]

    Experimental investigations of post-dryout heat transfer in 10 x 22.1 annulus test section with space. rs were carried out in the high-pressure two-phase flow loop at the Royal Institute of Technology (KTH). The test section was manufactured of Inconel 600 to withstand high temperatures. Several thermocouples were installed on tube and rod surfaces to measure the local wall temperature. Measurements were performed for mass flow rate in range from 500 to 2000 kg m(-2) s(-1), with inlet subcooling equal to 10 and 40 K, heat flux in a range from 480 to 1380 kW m(-2) and for the system pressure of 7 MPa. Uniform axial power distributions were applied on rod and tube walls. Using different distributions of heat flux between walls, post-dryout was achieved either on the inner or on the outer wall. The experimental results indicate a very strong influence of spacers on post-dryout heat transfer. For low mass flow rates the wall superheat was significantly reduced downstream of spacers, even though the whole distance between spacers was still under post-dryout conditions when heat flux was high enough. At high mass flow rates and under investigated range of heat flux the dryout patches were effectively quenched downstream of spacers.

  • 5.
    Ardekani, Mehdi Niazi
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Costa, Pedro
    Breugem, Wim Paul
    Brandt, Luca
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Numerical study of the sedimentation of spheroidal particles2016In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 87, p. 16-34Article in journal (Refereed)
    Abstract [en]

    The gravity-driven motion of-rigid particles in a viscous fluid is relevant in many natural and industrial processes, yet this has mainly been investigated for spherical particles. We therefore consider the sedimentation of non-spherical (spheroidal) isolated and particle pairs in a viscous fluid via numerical simulations using the Immersed Boundary Method. The simulations performed here show that the critical Galileo number for the onset of secondary motions decreases as the spheroid aspect ratio departs from 1. Above this critical threshold, oblate particles perform a zigzagging motion whereas prolate particles rotate around, the vertical axis while having their broad side facing the falling direction. Instabilities of the vortices in the wake follow when farther increasing the Galileo number. We also study the drafting kissing-tumbling associated with the settling of particle pairs. We find that the interaction time increases significantly for non-spherical particles and, more interestingly, spheroidal particles are attracted from larger lateral displacements. This has important implications for the estimation of collision kernels and can result its increasing clustering in suspensions of sedimenting spheroids.

  • 6.
    Carlson, Andreas
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Do-Quang, Minh
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Droplet dynamics in a bifurcating channel2010In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 36, no 5, p. 397-405Article in journal (Refereed)
    Abstract [en]

    In the present paper we present a phenomenological description of droplet dynamics in a bifurcating channel that is based on three-dimensional numerical experiments using the Phase Field theory. Droplet dynamics is investigated in a junction, which has symmetric outflow conditions in its daughter branches. We identify two different flow regimes as the droplets interact with the tip of the bifurcation, splitting and non-splitting. A distinct criterion for the flow regime transition is found based on the initial droplet volume and the Capillary (Ca) number. The Rayleigh Plateau instability is identified as a driving mechanism for the droplet breakup close to the threshold between the splitting and non-splitting regime.

  • 7.
    Fan, Wenyuan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Li, Haipeng
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering. Warsaw Univ Technol, Inst Heat Engn, 21-25 Nowowiejska St, PL-00665 Warsaw, Poland..
    Numerical investigation of spatial and temporal structure of annular flow with disturbance waves2019In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 110, p. 256-272Article in journal (Refereed)
    Abstract [en]

    Droplet entrainment is a crucial process for annular flow in terms of heat and mass transfer. Disturbance wave is believed to be a fundamental phenomenon which is closely related to entrainment. A 3D numerical simulation on disturbance waves and entrainment is carried out by using volume of fluid (VOF) method where no periodic boundary condition is used. Since VOF tracks the interface implicitly, a systematic method is developed for post-processing, with which disturbance waves. ripples, base film, and entrainment process are clearly visualized, and the stochastic and chaotic nature of two-phase flow is confirmed. Surfacewise distributions are generated for main wave parameters, and the streamwise developments of such quantities are shown to be consistent with experimental observations. Predictions for main wave parameters are in reasonable agreement with the experiment and empirical correlations. Current work shows the capability and promising application of investigating disturbance waves and entrainment with VOF method.

  • 8. Fukada, T.
    et al.
    Fornari, Walter
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Takeuchi, S.
    Kajishima, T.
    A numerical approach for particle-vortex interactions based on volume-averaged equations2018In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 104, p. 188-205Article in journal (Refereed)
    Abstract [en]

    To study the dynamics of particles in turbulence when their sizes are comparable to the smallest eddies in the flow, the Kolmogorov length scale, efficient and accurate numerical models for the particle-fluid interaction are still missing. Therefore, we here extend the treatment of the particle feedback on the fluid based on the volume-averaged fluid equations (VA simulation) in the previous study of the present authors, by estimating the fluid force correlated with the disturbed flow. We validate the model against interface-resolved simulations using the immersed-boundary method. Simulations of single particles show that the history effect is well captured by the present estimation method based on the disturbed flow. Similarly, the simulation of the flow around a rotating particle demonstrates that the lift force is also well captured by the proposed method. We also consider the interaction between non-negligible size particles and an array of Taylor–Green vortices. For density ratios ρd /ρc ≥ 10, the results show that the particle motion captured by the VA approach is closer to that of the fully-resolved simulations than that obtained with a traditional two-way coupling simulation. The flow disturbance is also well represented by the VA simulation. In particular, it is found that history effects enhance the curvature of the trajectory in vortices and this enhancement increases with the particle size. Furthermore, the flow field generated by a neighboring particle at distances of around ten particle diameters significantly influences particle trajectories. The computational cost of the VA simulation proposed here is considerably lower than that of the interface-resolved simulation.

  • 9. Fukagata, K.
    et al.
    Zahrai, S.
    Kondo, S.
    Bark, Fritz H.
    KTH, Superseded Departments, Mechanics.
    Anomalous velocity fluctuations in particulate turbulent channel flow2001In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 27, no 4, p. 701-719Article in journal (Refereed)
    Abstract [en]

    Gas-particle turbulent channel flow at Re-tau = 644, loaded with copper particles at a mass flow ratio of 2%, is studied numerically by large eddy simulation (LES) coupled with Lagrangian particle tracking (LPT), Inter-particle collisions and correction of drag force in the vicinity of walls are accounted for. Focus is made on the influence of particle wall boundary conditions and their influence on the statistical structure of the flow, It is shown that accordance with experimental data can be improved if a mechanism which can suppress the direct re-entrainment of particles after the impact at the wall is present. Present result shows that inter-particle collisions may play an important role in the re-distribution of particle momentum among different components even at low mass loading conditions,

  • 10.
    Gallego-Marcos, Ignacio
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Kudinov, Pavel
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Villanueva, Walter
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Puustinen, Markku
    Lappeenranta University of Technology (LUT), Finland.
    Räsänen, Antti
    Lappeenranta University of Technology (LUT), Finland.
    Tielinen, Kimmo
    Lappeenranta University of Technology (LUT), Finland.
    Kotro, Eetu
    Lappeenranta University of Technology (LUT), Finland.
    Effective momentum induced by steam condensation in the oscillatory bubble regimeIn: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533Article in journal (Refereed)
    Abstract [en]

    The spargers used in Boiling Water Reactors (BWR) discharge steam from the primary coolant system into a pool of water. Direct steam condensation in subcooled water creates sources of heat and momentum determined by the condensation regimes, called “effective sources” in this work. Competition between the effective sources can result in thermally stratification or mixing of the pool. Thermal stratification is a safety concern in BWRs since it reduces the steam condensation and pressure suppression capacity of the pool. In this work, we present semi-empirical correlations to predict the effective momentum induced by steam condensation in the oscillatory bubble regime, relevant for the operation of spargers in BWRs. A Separate Effect Facility (SEF) was designed and built at LUT, Finland, in order to provide the necessary data. An empirical correlation for the effective momentum as a function of the Jakob number is proposed. The Kelvin Impulse theory was also applied to estimate the effective momentum based on information about the bubble dynamics. To do this, new correlations for the bubble collapse frequencies, maximum bubble radius, velocities, pressure gradient and heat transfer coefficient are proposed and compared to available data from the literature. The effective momentum induced by sonic steam jets appears to be constant in a wide range of studied Jakob number. However, further experimental data is necessary at larger Jakob numbers and steam mass fluxes.

  • 11.
    Hyensjö, Marko
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Dahlkild, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Study of the rotational diffusivity coefficient of fibres in planar contracting flows with varying turbulence levels2008In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 34, no 9, p. 894-903Article in journal (Refereed)
    Abstract [en]

    The Fokker-Planck equation is solved by describing the evolution of a 3D fibre orientation state along a planar contraction. A constant value of the effective rotational diffusion coefficient was determined for four different turbulent flow cases in planar contractions, reported experimentally in the literature. Two hypotheses for the non-dimensional rotational diffusivity are presented, each based on two different turbulent time scales, i.e. the Kolmogorov time scales and the time scale associated with large energy bearing eddies. These hypotheses are dependent on either the Reynolds number, based on the Taylor micro-scale, and/or a non-dimensional fibre length. The hypothesis, based on the assumption of long fibres, L-t/n greater than or similar to 25, compared to the Kolmogorov scale and in the limit of large Re-lambda seems to capture the basic trends presented in the literature. This hypothesis has also the feature of predicting effects of varying fibre length within certain limits. Accordingly, by modeling the variation of turbulent quantities along the contraction in a CFD analysis, local values of rotational diffusivity can be evaluated with the mentioned hypothesis, based on either Kolmogorov time scale or Eulerian integral time scale.

  • 12.
    Jayawickrama, Thamali R.
    et al.
    Lulea Univ Technol, Div Energy Sci, Energy Engn, S-97187 Lulea, Sweden..
    Haugen, Nils Erland L.
    Norwegian Univ Sci & Technol, Dept Energy & Proc Engn, Kolbjorn Hejes Vei 1 B, N-7491 Trondheim, Norway.;SINTEF Energy Res, Dept Thermal Energy, Kolbjorn Hejes Vei 1 A, N-7491 Trondheim, Norway..
    Bäbler, Matthäus
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Chishty, M. A.
    Lulea Univ Technol, Div Energy Sci, Energy Engn, S-97187 Lulea, Sweden..
    Umeki, Kentaro
    Lulea Univ Technol, Div Energy Sci, Energy Engn, S-97187 Lulea, Sweden..
    The effect of Stefan flow on the drag coefficient of spherical particles in a gas flow2019In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 117, p. 130-137Article in journal (Refereed)
    Abstract [en]

    Particle laden flows with reactive particles are common in industrial applications. Chemical reactions inside the particle can generate a Stefan flow that affects heat, mass and momentum transfer between the particle and the bulk flow. This study aims at investigating the effect of Stefan flow on the drag coefficient of a spherical particle immersed in a uniform flow under isothermal conditions. Fully resolved simulations were carried out for particle Reynolds numbers ranging from 0.2 to 14 and Stefan flow Reynolds numbers from (-1) to 3, using the immersed boundary method for treating fluid-solid interactions. Results showed that the drag coefficient decreased with an increase of the outward Stefan flow. The main reason was the change in viscous force by the expansion of the boundary layer surrounding the particle. A simple model was developed based on this physical interpretation. With only one fitting parameter, the performance of the model to describe the simulation data were comparable to previous empirical models. The Authors.

  • 13.
    Kékesi, Timea
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Altimira, Mireia
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Amberg, Gustav
    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.
    Interaction between two deforming liquid drops in tandem and various off-axis arrangements subject to uniform flow2019In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, p. 193-218Article in journal (Refereed)
    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.

  • 14.
    Kékesi, Timea
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Amberg, Gustav
    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.
    Corrigendum to: "Drop deformation and breakup". Int. J. Multiphase Flow, 66, (2014) 1-102016In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533Article in journal (Refereed)
  • 15.
    Kékesi, Timea
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Drop deformation and breakup2014In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 66, p. 1-10Article in journal (Refereed)
    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.

  • 16.
    Lashgari, Iman
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Picano, Francesco
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. University of Padova, Italy.
    Breugem, Wim Paul
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Channel flow of rigid sphere suspensions: Particle dynamics in the inertial regime2016In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 78, p. 12-24Article in journal (Refereed)
    Abstract [en]

    We consider suspensions of neutrally-buoyant finite-size rigid spherical particles in channel flow and investigate the relation between the particle dynamics and the mean bulk behavior of the mixture for Reynolds numbers 500 ≤ Re ≤ 5000 and particle volume fraction 0 ≤ Φ ≤ 0.3, via fully resolved numerical simulations. Analysis of the momentum balance reveals the existence of three different regimes: laminar, turbulent and inertial shear-thickening depending on which of the stress terms, viscous, Reynolds or particle stress, is the major responsible for the momentum transfer across the channel. We show that both Reynolds and particle stress dominated flows fall into the Bagnoldian inertial regime and that the Bagnold number can predict the bulk behavior although this is due to two distinct physical mechanisms. A turbulent flow is characterized by larger particle dispersion and a more uniform particle distribution, whereas the particulate-dominated flows is associated with a significant particle migration towards the channel center where the flow is smooth laminar-like and dispersion low. Interestingly, the collision kernel shows similar values in the different regimes, although the relative particle velocity and clustering clearly vary with inertia and particle concentration.

  • 17. Lin, Yuan
    et al.
    Skjetne, Paal
    Carlson, Andreas
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A phase field model for multiphase electro-hydrodynamic flow2012In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 45, p. 1-11Article in journal (Refereed)
    Abstract [en]

    The principles of electro-hydrodynamics have been known for more than a century and extensive experimental studies have been carried out. Insight about such types of flows have been widely adopted for industrial applications, e.g. fluid mixing and de-mixing, but analytical solutions only exist in a limited number of cases, e.g. small deformation of a single droplet in a uniform and steady electric field. Numerical modeling of such phenomena can provide significant insights into electro-hydrodynamic multi-phase flows. In the present paper we propose a phase field model for studying two-phase electro-hydrodynamic flow generated by an electric field. The proposed model is validated and found to be in good agreement with existing analytical solutions and numerical studies in the literature. We also investigate the influence of viscosity ratio and surface tension in binary coalescence of drops in an immiscible fluid.

  • 18.
    Manickam, Louis
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Bechta, Sevostian
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    On the fragmentation characteristics of melt jets quenched in water2017In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 91, p. 262-275Article in journal (Refereed)
    Abstract [en]

    Experiments were carried out to investigate the characteristics of jet breakup and debris formation after melt jets fall into a subcooled water pool, which may occur in industrial processes such as the interactions of molten corium with coolant during a severe accident of light water reactors. A high-speed visualization system developed previously at KTH was used to capture the jet fragmentation phenomenon. Molten metal (Woods metal or tin) and mixture of binary oxides (WO3-Bi2O3 or WO3-ZrO2) were employed separately as melt materials to address different breakup mechanisms (e.g., hydrodynamic vs. thermodynamic fragmentation) and material effect. Moreover, the parameters related to melt and water conditions, including superheat, jet diameter and velocity of melt as well as subcooling of water, were scrutinized for their influences on jet fragmentation characteristics. The experimental data were acquired on the melt jet fragmentation patterns, breakup length, droplet size spectrum, droplet breakup and solidification as well as debris morphology, which can be useful for validation of the codes used for the prediction of debris formation phenomena.

  • 19. Martin-Callizo, Claudi
    et al.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Owhaib, Wahib
    Subcooled flow boiling of R-134a in vertical channels of small diameter2007In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 33, no 8, p. 822-832Article in journal (Refereed)
    Abstract [en]

    Subcooled flow boiling heat transfer for refrigerant R- 134a in vertical cylindrical tubes with 0.83, 1.22 and 1.70 turn internal diameter was experimentally investigated. The effects of the heat flux, q = 1-26 kW/m 2, mass flux, G = 300-700 kg /m(2) s, inlet subcooling, Delta T-sub,T-i = 5-15 degrees C, system pressure, P = 7.70-10.17 bar, and channel diameter, D, on the subcooled boiling heat transfer were explored in detail. The results are presented in the form of boiling curves and heat transfer coefficients. The boiling curves evidenced the existence of hysteresis when increasing the heat flux until the onset of nucleate boiling, ONB. The wall superheat at ONB was found to be essentially higher than that predicted with correlations for larger tubes. An increase of the mass flux leads, for early subcooled boiling, to an increase in the heat transfer coefficient. However, for fully developed subcooled boiling, increases of the mass flux only result in a slight improvement of the heat transfer. Higher inlet subcooling, higher system pressure and smaller channel diameter lead to better boiling heat transfer. Experimental heat transfer coefficients are compared to predictions from classical correlations available in the literature. None of them predicts the experimental data for all tested conditions.

  • 20.
    Ni, Peiyuan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Lage Lord Ingemar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Ersson, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    On the deposition of particles in liquid metals onto vertical ceramic walls2014In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 62, p. 152-160Article in journal (Refereed)
    Abstract [en]

    The deposition of non-metallic particles in liquid-metal flows is a serious industrial problem because the build-up of particles on ceramic walls clogs the flow path and interrupts the production, and this leads to large economic losses. This paper is an effort to extend the current state-of-the-art knowledge of particle deposition in air in order to predict particle deposition rates in liquid-metal flows using an improved Eulerian deposition model and considering Brownian and turbulent diffusion, turbophoresis and thermophoresis as transportation mechanisms. The model was used to predict the rate of deposition of particles in an air flow, and the predictions were compared to published measurements to demonstrate its performance. The model was then modified to take into account the differences in properties between air and liquid metals and thereafter applied to liquid-metal flows. Effects on the deposition rate of parameters such as steel flow rate, particle diameter, particle density, wall roughness and temperature gradient near the wall were investigated. It is shown that the steel flow rate has a very important influence on the rate of deposition of large particles, for which turbophoresis is the main deposition mechanism. For small particles, both wall roughness and thermophoresis have a significant influence on the particle deposition rate. Particle deposition rates under various conditions were successfully predicted.

  • 21. Nourgaliev, R. R.
    et al.
    Dinh, Truc-Nam
    Theofanous, T. G.
    A pseudocompressibility method for the numerical simulation of incompressible multifluid flows2004In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 30, no 7-8, p. 901-937Article in journal (Refereed)
    Abstract [en]

    This paper presents an explicit characteristics-based, conservative, finite-difference method for the simulation of incompressible multiphase flows. The method is based on the artificial compressibility concept, e,,tended to variable-density, and uses a time stretching procedure to relieve the acoustic constrain. We take advantage of the algorithmic simplicity and hyperbolicity provided by the artificial compressibility to develop a flow solver that is numerically robust, accurate and effective for massively parallel computations of incompressible multifluid flows. The resulting method, named Numerical Acoustic Relaxation or NAR, is a combination of the AC concept with the Level Set method for interface-capturing and the Ghost-Fluid method to compute flows with multiple, arbitrary density variation, free or stationary interfaces. In this paper we demonstrate convergence and accuracy of the solver by computing such standard test problems as the Lid-Driven Cavity and Doubly Periodic Shear Layer. Competitiveness with approximate projection, vorticity stream function, pseudospectral, and Lattice Boltzmann Equation is also discussed. In addition, we demonstrate the interface-capturing features of NAR by means of the simple Rayleigh-Taylor and Water Column Collapse problems.

  • 22. Nourgaliev, R. R.
    et al.
    Dinh, Truc-Nam
    Theofanous, T. G.
    Joseph, D.
    The lattice Boltzmann equation method: theoretical interpretation, numerics and implications2003In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 29, no 1, p. 117-169Article, review/survey (Refereed)
    Abstract [en]

    During the last ten years the lattice Boltzmann equation (LBE) method has been developed as an alternative numerical approach in computational fluid dynamics (CFD). Originated from the discrete kinetic theory, the LBE method has emerged with the promise to become a superior modeling platform, both computationally and conceptually, compared to the existing arsenal of the continuum-based CFD methods. The LBE method has been applied for simulation of various kinds of fluid flows under different conditions. The number of papers on the LBE method and its applications continues to grow rapidly, especially in the direction of complex and multiphase media. The purpose of the present paper is to provide a comprehensive, self-contained and consistent tutorial on the LBE method, aiming to clarify misunderstandings and eliminate some confusion that seems to persist in the LBE-related CFD literature. The focus is placed on the fundamental principles of the LBE approach. An excursion into the history, physical background and details of the theory and numerical implementation is made. Special attention is paid to advantages and limitations of the method, and its perspectives to be a useful framework for description of complex flows and interfacial (and multiphase) phenomena. The computational performance of the LBE method is examined, comparing it to other CFD methods, which directly solve for the transport equations of the macroscopic variables.

  • 23. Nourgaliev, R. R.
    et al.
    Sushchikh, S. Y.
    Dinh, Truc-Nam
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Theofanous, T. G.
    Shock wave refraction patterns at interfaces2005In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 31, no 9, p. 969-995Article in journal (Refereed)
    Abstract [en]

    Interactions of shock waves with gas-gas and gas-liquid interfaces (under both slow-fast and fast-slow configurations) are studied using the recently developed Adaptive Characteristics-based Matching (aCBM) method for capturing interfaces in compressible multi-fluid media. First, we verify our approach for the gas-gas case; a class of problems for which a substantial body of knowledge already exists. Then, we consider slow-fast, gas-liquid interfaces under weak shocks, and fast-slow, liquid-gas interfaces under strong shocks. The very high acoustic impedance mismatch situation here creates significant numerical (simulation) and experimental (visualization) difficulties, and the literature for it is meager and sporadic. Compared to gas-gas interfaces we note both similarities and differences. We discuss the sources for these differences, as well as potential implications of generalizing and embedding such results in multi-dimensional simulation schemes towards improving their front-capturing performance.

  • 24. Prahl Wittberg, Lisa
    et al.
    Hoelzer, A.
    Arlov, D.
    Revstedt, J.
    Sommerfeld, M.
    Fuchs, Laszlo
    On the interaction between two fixed spherical particles2007In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 33, no 7, p. 707-725Article in journal (Refereed)
    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.

  • 25.
    Prahl Wittberg, Lisa
    et al.
    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. KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Jadoon, A.
    Revstedt, J.
    Interaction between two spheres placed in tandem arrangement in steady and pulsating flow2009In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 35, no 10, p. 963-969Article in journal (Refereed)
    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.

  • 26. Salewski, Mirko
    et al.
    Fuchs, Laszlo
    Consistency issues of Lagrangian particle tracking applied to a spray jet in crossflow2007In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 33, no 4, p. 394-410Article in journal (Refereed)
    Abstract [en]

    Numerical simulations are performed for multiphase jets in crossflow. The flow solver uses an Eulerian/Lagrangian approach. Turbulence in the gas phase is modeled in the framework of large eddy simulation. The dispersed phase is handled using Lagrangian particle tracking. The model assumptions of solvers for Lagrangian particle tracking are critically assessed for typical flow conditions of spray jets in crossflow. The droplets are assumed to be spherical and isolated. It is shown that several model assumptions are apparently inconsistent in larger portions of the flow field. Firstly, average Weber numbers can be so large that the model assumption to regard droplets as spherical is questionable, not only near the nozzle, but also in the far-field. Secondly, the average droplet spacing can be so low that droplets directly interact with each other, again also in the far-field. Thirdly, the average Stokes numbers in the jet region can be so large that the phase coupling between the dispersed and continuous phase is weak. Some remedies to these deficiencies are proposed.

  • 27.
    Villanueva, Walter
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Some generic capillary-driven flows2006In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 32, no 8, p. 1072-1086Article in journal (Refereed)
    Abstract [en]

    This paper deals with numerical simulations of some capillary-driven flows. The focus is on the wetting phenomenon in sintering-like flows and in the imbibition of liquids into a porous medium. The wetting phenomenon is modeled using the coupled Cahn-Hilliard/Navier-Stokes system. The Cahn-Hilliard equation is treated as a system where the chemical potential is solved first followed by the composition. The equations are discretised in space using piecewise linear functions. Adaptive finite element method is implemented with an ad hoc error criterion that ensures mesh resolution along the vicinity of the interface. In the 3D case we use parallel adaptive finite element method. First, a basic wetting of a liquid drop on a solid surface is shown and is established the independence of the dynamic contact angle on the interface width. In addition, the dependence of the dynamic contact angle on the Capillary number is matched with experimental data. Next, some generic sintering-like flows with a fixed matrix is presented. Different geometries in 2D and 3D are considered. We observed rapid wetting, precursor films, coalescence, breakup of melt drops as well as pore migration and elimination that are all microstructural characteristics of a liquid phase sintering. Finally, the effect of equilibrium contact angles on imbibition of liquid into a porous medium is studied.

  • 28.
    Wang, Yuli
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Gratadeix, Anthony
    Do-Quang, Minh
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Events and conditions in droplet impact: a phase field prediction2016In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 87, p. 54-65Article in journal (Refereed)
    Abstract [en]

    The phenomenon of droplet impact on a smooth, flat, partially wetted surface is studied by phase field simulation. A map of the different impact regimes is constructed for Reynolds numbers ranging from Re = 9 to Re = 9 x 10(4), and Ohnesorge numbers ranging from Oh = 3.3 x 10(-4) to Oh = 1.05. The results are compared with previous experiments from several aspects such as gas bubble entrapment, spreading radius and liquid sheet splashing, etc. The simulation proposes event predictions that are consistent with previous experiments. Our results and discussions give an overview of important characteristics during droplet impact, and provide insights on the droplet spreading after impact.

  • 29.
    Zade, Sagar
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Turbulence modulation by finite-size spherical particles in Newtonian and viscoelastic fluids2019In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 112, p. 116-129Article in journal (Refereed)
    Abstract [en]

    We experimentally investigate the influence of finite-size spherical particles in turbulent flows of a Newtonian and a drag reducing viscoelastic fluid at varying particle volume fractions and fixed Reynolds number. Experiments are performed in a square duct at a Reynolds number Re2H of nearly 1.1 × 104, Weissenberg number Wi for single phase flow is between 1 and 2 and results in a drag-reduction of 43% compared to a Newtonian flow (at the same Re2H). Particles are almost neutrally-buoyant hydrogel spheres having a density ratio of 1.0035 ± 0.0003 and a duct height 2H to particle diameter dp ratio of around 10. We measure flow statistics for four different volume fractions ϕ namely 5, 10, 15 and 20% by using refractive-index-matched Particle Image Velocimetry (PIV). For both Newtonian Fluid (NF) and Visceolastic Fluid (VEF), the drag monotonically increases with ϕ. For NF, the magnitude of drag increase due to particle addition can be reasonably estimated using a concentration dependent effective viscosity for volume fractions below 10%. The drag increase is, however, underestimated at higher ϕ. For VEF, the absolute value of drag is lower than NF but, its rate of increase with ϕ is higher. Similar to particles in a NF, particles in VEF tend to migrate towards the center of the duct and form a layer of high concentration at the wall. Interestingly, relatively higher migration towards the center and lower migration towards the walls is observed for VEF. The primary Reynolds shear stress reduces with increasing ϕ throughout the duct height for both types of fluid.

  • 30.
    Zampogna, Giuseppe A.
    et al.
    Univ Genoa, Scuola Politecn, DICCA, Via Montallegro 1, I-16145 Genoa, Italy..
    Lacis, Ugis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Bagheri, Shervin
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Bottaro, Alessandro
    Univ Genoa, Scuola Politecn, DICCA, Via Montallegro 1, I-16145 Genoa, Italy..
    Modeling waves in fluids flowing over and through poroelastic media2019In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 110, p. 148-164Article in journal (Refereed)
    Abstract [en]

    Multiscale homogenization represents a powerful tool to treat certain fluid-structure interaction problems involving porous, elastic, fibrous media. This is shown here for the case of the interaction between a Newtonian fluid and a poroelastic, microstructured material. Microscopic problems are set up to determine effective tensorial properties (elasticity, permeability, porosity, bulk compliance of the solid skeleton) of the homogenized medium, both in the interior and at its boundary with the fluid domain, and an extensive description is provided of such properties for varying porosity. The macroscopic equations which are derived by homogenization theory employ such effective properties thus permitting the computation of velocities and displacements within the poroelastic mixture for two representative configurations of standing and travelling waves.

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