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Publications (10 of 167) Show all publications
Fukada, T., Fornari, W., Brandt, L., Takeuchi, S. & Kajishima, T. (2018). A numerical approach for particle-vortex interactions based on volume-averaged equations. International Journal of Multiphase Flow, 104, 188-205
Open this publication in new window or tab >>A numerical approach for particle-vortex interactions based on volume-averaged equations
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2018 (English)In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 104, p. 188-205Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
History effect, Particle-laden flow, Particle-vortex interaction, Volume-averaged equation
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-227530 (URN)10.1016/j.ijmultiphaseflow.2018.02.019 (DOI)000432643700015 ()2-s2.0-85043509672 (Scopus ID)
Funder
EU, European Research Council, ERC-2013-CoG-616186Swedish Research CouncilSwedish e‐Science Research CenterSwedish National Infrastructure for Computing (SNIC)
Note

QC 20180517

Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2018-06-13Bibliographically approved
Sardina, G., Picano, F., Brandt, L. & Caballero, R. (2018). Direct and large eddy simulations of droplet condensation in turbulent warm clouds. In: : . Paper presented at ERCOFTAC 2017 (pp. 475-481). Springer Netherland
Open this publication in new window or tab >>Direct and large eddy simulations of droplet condensation in turbulent warm clouds
2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A cloud is a complex multiphase system constituted by a huge number of different substances such as water droplets, ice droplets, water vapor, organic vapors, air.

Place, publisher, year, edition, pages
Springer Netherland, 2018
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:kth:diva-227097 (URN)10.1007/978-3-319-63212-4_61 (DOI)2-s2.0-85031892727 (Scopus ID)
Conference
ERCOFTAC 2017
Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-05-15Bibliographically approved
Ge, Z., Holmgren, H., Kronbichler, M., Brandt, L. & Kreiss, G. (2018). Effective slip over partially filled microcavities and its possible failure. Physical Review Fluids, 3(5), Article ID 054201.
Open this publication in new window or tab >>Effective slip over partially filled microcavities and its possible failure
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2018 (English)In: Physical Review Fluids, ISSN 2469-990X, Vol. 3, no 5, article id 054201Article in journal (Refereed) Published
Abstract [en]

Motivated by the emerging applications of liquid-infused surfaces (LIS), we study the drag reduction and robustness of transverse flows over two-dimensional microcavities partially filled with an oily lubricant. Using separate simulations at different scales, characteristic contact line velocities at the fluid-solid intersection are first extracted from nanoscale phase field simulations and then applied to micronscale two-phase flows, thus introducing a multiscale numerical framework to model the interface displacement and deformation within the cavities. As we explore the various effects of the lubncant-toouter-fluid viscosity ratio A2/A0 th(mu)over tilde( )c(mu)over tilde(1), thary number Ca, the static contact angle A> and t theta(s), filling fraction of the cavity <5, we f delta d that the effective slip is most sensitive to the parameter S. The effects of A2/A1 an(mu)over tilde( )A(mu)over tilde(a )re ge theta(s)erally intertwined but weakened if <5 < 1. delta M 1er, for an initial filling fraction S = 0.94 delta our results show that the effective slip is nearly independent of the capillary number when it is small. Further increasing Ca to about O.OIA1/A20.01(mu)over tilde(1)/(mu)over tilde(2)ntify a possible failure mode, associated with lubricants draining from the LIS, for A2/A1 A (mu)over tilde(2)1(mu)over tilde(1)V less than or similar to y viscous lubricants (e.g., A2/A1 > (mu)over tilde()),(mu)over tilde(h)owever, are immune to such failure due to their generally larger contact line velocity.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-230443 (URN)10.1103/PhysRevFluids.3.054201 (DOI)000433036100003 ()
Funder
Swedish Research Council, 621-2012-2360EU, FP7, Seventh Framework Programme, 664823Swedish e‐Science Research Center
Note

QC 20180613

Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-06-15Bibliographically approved
Costa, P., Picano, F., Brandt, L. & Breugem, W.-P. (2018). Effects of the finite particle size in turbulent wall-bounded flows of dense suspensions. Journal of Fluid Mechanics, 843, 450-478
Open this publication in new window or tab >>Effects of the finite particle size in turbulent wall-bounded flows of dense suspensions
2018 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 843, p. 450-478Article in journal (Refereed) Published
Abstract [en]

We use interface-resolved numerical simulations to study finite-size effects in turbulent channel flow of neutrally buoyant spheres. Two cases with particle sizes differing by a factor of two, at the same solid volume fraction of 20% and bulk Reynolds number are considered. These are complemented with two reference single-phase flows: the unladen case, and the flow of a Newtonian fluid with the effective suspension viscosity of the same mixture in the laminar regime. As recently highlighted in Costa etal. (Phys. Rev. Lett., vol.117, 2016, 134501), a particle-wall layer is responsible for deviations of the mesoscale-averaged statistics from what is observed in the continuum limit where the suspension is modelled as a Newtonian fluid with (higher) effective viscosity. Here we investigate in detail the fluid and particle dynamics inside this layer and in the bulk. In the particle-wall layer, the near-wall inhomogeneity has an influence on the suspension microstructure over a distance proportional to the particle size. In this layer, particles have a significant (apparent) slip velocity that is reflected in the distribution of wall shear stresses. This is characterized by extreme events (both much higher and much lower than the mean). Based on these observations we provide a scaling for the particle-to-fluid apparent slip velocity as a function of the flow parameters. We also extend the scaling laws in Costa etal. (Phys. Rev. Lett., vol.117, 2016, 134501) to second-order Eulerian statistics in the homogeneous suspension region away from the wall. The results show that finite-size effects in the bulk of the channel become important for larger particles, while negligible for lower-order statistics and smaller particles. Finally, we study the particle dynamics along the wall-normal direction. Our results suggest that single-point dispersion is dominated by particle-turbulence (and not particle-particle) interactions, while differences in two-point dispersion and collisional dynamics are consistent with a picture of shear-driven interactions.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2018
Keywords
multiphase and particle-laden flows, particle/fluid flows suspensions, turbulent flows
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-225710 (URN)10.1017/jfm.2018.117 (DOI)000428165000001 ()2-s2.0-85044259159 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20180411

Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-04-11Bibliographically approved
De Vita, F., Rosti, M. E., Izbassarov, D., Duffo, L., Tammisola, O., Hormozi, S. & Brandt, L. (2018). Elastoviscoplastic flows in porous media. Journal of Non-Newtonian Fluid Mechanics, 258, 10-21
Open this publication in new window or tab >>Elastoviscoplastic flows in porous media
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2018 (English)In: Journal of Non-Newtonian Fluid Mechanics, ISSN 0377-0257, E-ISSN 1873-2631, Vol. 258, p. 10-21Article in journal (Refereed) Published
Abstract [en]

We investigate the elastoviscoplastic flow through porous media by numerical simulations. We solve the Navier–Stokes equations combined with the elastoviscoplastic model proposed by Saramito for the stress tensor evolution [1]. In this model, the material behaves as a viscoelastic solid when unyielded, and as a viscoelastic Oldroyd-B fluid for stresses higher than the yield stress. The porous media is made of a symmetric array of cylinders, and we solve the flow in one periodic cell. We find that the solution is time-dependent even at low Reynolds numbers as we observe oscillations in time of the unyielded region especially at high Bingham numbers. The volume of the unyielded region slightly decreases with the Reynolds number and strongly increases with the Bingham number; up to 70% of the total volume is unyielded for the highest Bingham numbers considered here. The flow is mainly shear dominated in the yielded region, while shear and elongational flow are equally distributed in the unyielded region. We compute the relation between the pressure drop and the flow rate in the porous medium and present an empirical closure as function of the Bingham and Reynolds numbers. The apparent permeability, normalized with the case of Newtonian fluids, is shown to be greater than 1 at low Bingham numbers, corresponding to lower pressure drops due to the flow elasticity, and smaller than 1 for high Bingham numbers, indicating larger dissipation in the flow owing to the presence of the yielded regions. Finally we investigate the effect of the Weissenberg number on the distribution of the unyielded regions and on the pressure gradient.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Darcy's law, Elastoviscoplastic fluid, Porous media
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-227512 (URN)10.1016/j.jnnfm.2018.04.006 (DOI)2-s2.0-85045699057 (Scopus ID)
Funder
Swedish Research Council, VR 2014-5001, VR 2017-76478, VR 2013-5789EU, European Research Council, ERC-2013-CoG-616186Swedish e‐Science Research Center
Note

QC 20180518

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-05-18Bibliographically approved
Niazi Ardekani, M., Asmar, L. A., Picano, F. & Brandt, L. (2018). Numerical study of heat transfer in laminar and turbulent pipe flow with finite-size spherical particles. International Journal of Heat and Fluid Flow, 71, 189-199
Open this publication in new window or tab >>Numerical study of heat transfer in laminar and turbulent pipe flow with finite-size spherical particles
2018 (English)In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 71, p. 189-199Article in journal (Refereed) Published
Abstract [en]

Controlling heat and mass transfer in particulate suspensions has many applications in fuel combustion, food industry, pollution control and life science. We perform direct numerical simulations (DNS) to study the heat transfer within a suspension of neutrally buoyant, finite-size spherical particles in laminar and turbulent pipe flows, using the immersed boundary method (IBM) to account for the solid fluid interactions and a volume of fluid (VoF) method to resolve the temperature equation both inside and outside the particles. Particle volume fractions up to 40% are simulated for different pipe to particle diameter ratios. We show that a considerable heat transfer enhancement (up to 330%) can be achieved in the laminar regime by adding spherical particles. The heat transfer is observed to increase significantly as the pipe to particle diameter ratio decreases for the parameter range considered here. Larger particles are found to have a greater impact on the heat transfer enhancement than on the wall-drag increase. In the turbulent regime, however, only a transient increase in the heat transfer is observed and the process decelerates in time below the values in single-phase flows as high volume fractions of particles laminarize the core region of the pipe. A heat transfer enhancement, measured with respect to the single phase flow, is only achieved at volume fractions as low as 5% in a turbulent flow.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Finite-size particles, Heat transfer, Particulate flows, Pipe flows
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-227551 (URN)10.1016/j.ijheatfluidflow.2018.04.002 (DOI)2-s2.0-85045214851 (Scopus ID)
Funder
Swedish e‐Science Research Center
Note

QC 20180517

Available from: 2018-05-17 Created: 2018-05-17 Last updated: 2018-05-17Bibliographically approved
Rosti, M. E., Brandt, L. & Mitra, D. (2018). Rheology of suspensions of viscoelastic spheres: Deformability as an effective volume fraction. PHYSICAL REVIEW FLUIDS, 3(1), Article ID 012301.
Open this publication in new window or tab >>Rheology of suspensions of viscoelastic spheres: Deformability as an effective volume fraction
2018 (English)In: PHYSICAL REVIEW FLUIDS, ISSN 2469-990X, Vol. 3, no 1, article id 012301Article in journal (Refereed) Published
Abstract [en]

We study suspensions of deformable (viscoelastic) spheres in a Newtonian solvent in planeCouette geometry, by means of direct numerical simulations. We find that in the limit of vanishing inertia, the effective viscosity mu of the suspension increases as the volume fraction occupied by the spheres Phi increases and decreases as the elastic modulus of the spheres G decreases; the function mu(Phi,G) collapses to a universal function mu(Phi(e)) with a reduced effective volume fraction Phi(e)(Phi,G). Remarkably, the function mu(Phi(e)) is the well- known Eilers fit that describes the rheology of suspension of rigid spheres at all Phi. Our results suggest different ways to interpret the macrorheology of blood.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-222424 (URN)10.1103/PhysRevFluids.3.012301 (DOI)000423329600002 ()2-s2.0-85041513824 (Scopus ID)
Note

QC 20180228

Available from: 2018-02-28 Created: 2018-02-28 Last updated: 2018-05-24Bibliographically approved
Fornari, W., Picano, F. & Brandt, L. (2018). The effect of polydispersity in a turbulent channel flow laden with finite-size particles. European journal of mechanics. B, Fluids, 67, 54-64
Open this publication in new window or tab >>The effect of polydispersity in a turbulent channel flow laden with finite-size particles
2018 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 67, p. 54-64Article in journal (Refereed) Published
Abstract [en]

We study turbulent channel flows of monodisperse and polydisperse suspensions of finite-size spheres by means of Direct Numerical Simulations using an immersed boundary method to account for the dispersed phase. Suspensions with 3 different Gaussian distributions of particle radii are considered (i.e. 3 different standard deviations). The distributions are centered on the reference particle radius of the monodisperse suspension. In the most extreme case, the radius of the largest particles is 4 times that of the smaller particles. We consider two different solid volume fractions, 2% and 10%. We find that for all polydisperse cases, both fluid and particles statistics are not substantially altered with respect to those of the monodisperse case. Mean streamwise fluid and particle velocity profiles are almost perfectly overlapping. Slightly larger differences are found for particle velocity fluctuations. These increase close to the wall and decrease towards the centerline as the standard deviation of the distribution is increased. Hence, the behavior of the suspension is mostly governed by excluded volume effects regardless of particle size distribution (at least for the radii here studied). Due to turbulent mixing, particles are uniformly distributed across the channel. However, smaller particles can penetrate more into the viscous and buffer layer and velocity fluctuations are therein altered. Non trivial results are presented for particle-pair statistics.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Suspensions, Particle-laden flows, Particle/fluid flow
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-217629 (URN)10.1016/j.euromechflu.2017.08.003 (DOI)000418726900005 ()2-s2.0-85028452609 (Scopus ID)
Funder
Swedish Research CouncilSwedish e‐Science Research Center
Note

QC 20171116

Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2018-01-11Bibliographically approved
Fornari, W., Niazi Ardekani, M. & Brandt, L. (2017). Clustering and increased settling speed of oblate particles at finite Reynolds number. Journal of Fluid Mechanics
Open this publication in new window or tab >>Clustering and increased settling speed of oblate particles at finite Reynolds number
2017 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645Article in journal (Refereed) Submitted
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-217630 (URN)
Note

QC 20171116

Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2018-02-26Bibliographically approved
Ezhova, E., Cenedese, C. & Brandt, L. (2017). Dynamics of a turbulent Buoyant Plume in a stratified fluid: An idealized model of subglacial discharge in Greenland Fjords. Journal of Physical Oceanography, 47(10), 2611-2630
Open this publication in new window or tab >>Dynamics of a turbulent Buoyant Plume in a stratified fluid: An idealized model of subglacial discharge in Greenland Fjords
2017 (English)In: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 47, no 10, p. 2611-2630Article in journal (Refereed) Published
Abstract [en]

This study reports the results of large-eddy simulations of an axisymmetric turbulent buoyant plume in a stratified fluid. The configuration used is an idealized model of the plume generated by a subglacial discharge at the base of a tidewater glacier with an ambient stratification typical of Greenland fjords. The plume is discharged from a round source of various diameters and characteristic stratifications for summer and winter are considered. The classical theory for the integral parameters of a turbulent plume in a homogeneous fluid gives accurate predictions in the weakly stratified lower layer up to the pycnocline, and the plume dynamics are not sensitive to changes in the source diameter. In winter, when the stratification is similar to an idealized two-layer case, turbulent entrainment and generation of internal waves by the plume top are in agreement with the theoretical and numerical results obtained for turbulent jets in a two-layer stratification. In summer, instead, the stratification is more complex and turbulent entrainment by the plume top is significantly reduced. The subsurface layer in summer is characterized by a strong density gradient and the oscillating plume generates internal waves that might serve as an indicator of submerged plumes not penetrating to the surface.

Place, publisher, year, edition, pages
American Meteorological Society, 2017
Keywords
Buoyancy, Internal waves, Jets, Large eddy simulations, Oscillations, Turbulence
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:kth:diva-217570 (URN)10.1175/JPO-D-16-0259.1 (DOI)000414154400013 ()2-s2.0-85032733974 (Scopus ID)
Funder
Swedish e‐Science Research Center
Note

QC 20171117

Available from: 2017-11-17 Created: 2017-11-17 Last updated: 2017-11-24Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-4346-4732

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