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Publications (10 of 176) 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
Fornari, W., Niazi Ardekani, M. & Brandt, L. (2018). Clustering and increased settling speed of oblate particles at finite Reynolds number. Journal of Fluid Mechanics, 848, 696-721
Open this publication in new window or tab >>Clustering and increased settling speed of oblate particles at finite Reynolds number
2018 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 848, p. 696-721Article in journal (Refereed) Published
Abstract [en]

We study the settling of rigid oblates in a quiescent fluid using interface-resolved direct numerical simulations. In particular, an immersed boundary method is used to account for the dispersed solid phase together with lubrication correction and collision models to account for short-range particle-particle interactions. We consider semi-dilute suspensions of oblate particles with aspect ratio AR = 1/3 and solid volume fractions (Phi = 0.5-10%. The solid-to-fluid density ratio R = 1.02 and the Galileo number (i.e. the ratio between buoyancy and viscous forces) based on the diameter of a sphere with equivalent volume Ga = 60. With this choice of parameters, an isolated oblate falls vertically with a steady wake with its broad side perpendicular to the gravity direction. At this Ga, the mean settling speed of spheres is a decreasing function of the volume Phi and is always smaller than the terminal velocity of the isolated particle, V-t. On the contrary, in dilute suspensions of oblate particles (with Phi <= 1 %), the mean settling speed is approximately 33 % larger than V-t. At higher concentrations, the mean settling speed decreases becoming smaller than the terminal velocity V-t between (Phi = 5 % and 10%. The increase of the mean settling speed is due to the formation of particle clusters that for Phi = 0.5-1 % appear as columnar-like structures. From the pair distribution function we observe that it is most probable to find particle pairs almost vertically aligned. However, the pair distribution function is non-negligible all around the reference particle indicating that there is a substantial amount of clustering at radial distances between 2 and 6c (with c the polar radius of the oblate). Above Phi = 5 %, the hindrance becomes the dominant effect, and the mean settling speed decreases below V-t. As the particle concentration increases, the mean particle orientation changes and the mean pitch angle (the angle between the particle axis of symmetry and gravity) increases from 23 degrees to 47 degrees . Finally, we increase Ga from 60 to 140 for the case with (Phi = 0.5 % and find that the mean settling speed (normalized by V-t) decreases by less than 1 % with respect to Ga = 60. However, the fluctuations of the settling speed around the mean are reduced and the probability of finding vertically aligned particle pairs increases.

Place, publisher, year, edition, pages
Cambridge University Press, 2018
Keywords
multiphase and particle-laden flows, particle/fluid flow, suspensions
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-232594 (URN)10.1017/jfm.2018.370 (DOI)000438342800001 ()2-s2.0-85048603916 (Scopus ID)
Funder
EU, European Research Council, ERC-2013-CoG-616186Swedish Research CouncilSwedish e‐Science Research Center
Note

QC 20180731

Available from: 2018-07-31 Created: 2018-07-31 Last updated: 2018-07-31Bibliographically 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)000448592600061 ()2-s2.0-85031892727 (Scopus ID)978-3-319-63211-7 (ISBN)
Conference
ERCOFTAC 2017
Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-11-16Bibliographically approved
Ezhova, E., Cenedese, C. & Brandt, L. (2018). Dynamics of Three-Dimensional Turbulent Wall Plumes and Implications for Estimates of Submarine Glacier Melting. Journal of Physical Oceanography, 48(9), 1941-1950
Open this publication in new window or tab >>Dynamics of Three-Dimensional Turbulent Wall Plumes and Implications for Estimates of Submarine Glacier Melting
2018 (English)In: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 48, no 9, p. 1941-1950Article in journal (Refereed) Published
Abstract [en]

Subglacial discharges have been observed to generate buoyant plumes along the ice face of Greenland tidewater glaciers. These plumes have been traditionally modeled using classical plume theory, and their characteristic parameters (e.g., velocity) are employed in the widely used three-equation melt parameterization. However, the applicability of plume theory for three-dimensional turbulent wall plumes is questionable because of the complex near-wall plume dynamics. In this study, corrections to the classical plume theory are introduced to account for the presence of a wall. In particular, the drag and entrainment coefficients are quantified for a three-dimensional turbulent wall plume using data from direct numerical simulations. The drag coefficient is found to be an order of magnitude larger than that for a boundary layer flow over a flat plate at a similar Reynolds number. This result suggests a significant increase in the melting estimates by the current parameterization. However, the volume flux in a wall plume is found to be one-half that of a conical plume that has 2 times the buoyancy flux. This finding suggests that the total entrainment (per unit area) of ambient water is the same and that the plume scalar characteristics (i.e., temperature and salinity) can be predicted reasonably well using classical plume theory.

Place, publisher, year, edition, pages
American Meteorological Society, 2018
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-234574 (URN)10.1175/JPO-D-17-0194.1 (DOI)000442729400001 ()
Note

QC 20180917

Available from: 2018-09-17 Created: 2018-09-17 Last updated: 2018-09-17Bibliographically 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 ()2-s2.0-85049006815 (Scopus ID)
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: 2018-10-16Bibliographically 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
Rosti, M. E., Banaei, A. A., Brandt, L. & Mazzino, A. (2018). Flexible Fiber Reveals the Two-Point Statistical Properties of Turbulence. Physical Review Letters, 121(4), Article ID 044501.
Open this publication in new window or tab >>Flexible Fiber Reveals the Two-Point Statistical Properties of Turbulence
2018 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 4, article id 044501Article in journal (Refereed) Published
Abstract [en]

We study the dynamics of a flexible fiber freely moving in a three-dimensional fully developed turbulent field and present a phenomenological theory to describe the interaction between the fiber elasticity and the turbulent flow. This theory leads to the identification of two distinct regimes of flapping, which we validate against direct numerical simulations fully resolving the fiber dynamics. The main result of our analysis is the identification of a flapping regime where the fiber, despite its elasticity, is slaved to the turbulent fluctuations. In this regime the fiber can be used to measure two-point statistical observables of turbulence, including scaling exponents of velocity structure functions, the sign of the energy cascade and the energy flux of turbulence, as well as the characteristic times of the eddies within the inertial range of scales. Our results are expected to have a deep impact on the experimental turbulence research as a new way, accurate and efficient, to measure two-point, and more generally multipoint, statistics of turbulence.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-232886 (URN)10.1103/PhysRevLett.121.044501 (DOI)000439547100006 ()2-s2.0-85050744852 (Scopus ID)
Note

QC 20180809

Available from: 2018-08-09 Created: 2018-08-09 Last updated: 2018-08-09Bibliographically approved
Alghalibi, D., Lashgari, I., Brandt, L. & Hormozi, S. (2018). Interface-resolved simulations of particle suspensions in Newtonian, shear thinning and shear thickening carrier fluids. Journal of Fluid Mechanics, 852, 329-357
Open this publication in new window or tab >>Interface-resolved simulations of particle suspensions in Newtonian, shear thinning and shear thickening carrier fluids
2018 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 852, p. 329-357Article in journal (Refereed) Published
Abstract [en]

We present a numerical study of non-colloidal spherical and rigid particles suspended in Newtonian, shear thinning and shear thickening fluids employing an immersed boundary method. We consider a linear Couette configuration to explore a wide range of solid volume fractions (0.1 <= Phi <= 0.4) and particle Reynolds numbers (0.1 <= Re<INF>p</INF><INF></INF> <= 10). We report the distribution of solid and fluid phase velocity and solid volume fraction and show that close to the boundaries inertial effects result in a significant slip velocity between the solid and fluid phase. The local solid volume fraction profiles indicate particle layering close to the walls, which increases with the nominal Phi. This feature is associated with the confinement effects. We calculate the probability density function of local strain rates and compare the latter's mean value with the values estimated from the homogenisation theory of Chateau et al. (J. Rheol., vol. 52, 2008, pp. 489-506), indicating a reasonable agreement in the Stokesian regime. Both the mean value and standard deviation of the local strain rates increase primarily with the solid volume fraction and secondarily with the Re<INF>p</INF>. The wide spectrum of the local shear rate and its dependency on Phi and Re<INF>p</INF> point to the deficiencies of the mean value of the local shear rates in estimating the rheology of these non-colloidal complex suspensions. Finally, we show that in the presence of inertia, the effective viscosity of these non-colloidal suspensions deviates from that of Stokesian suspensions. We discuss how inertia affects the microstructure and provide a scaling argument to give a closure for the suspension shear stress for both Newtonian and power-law suspending fluids. The stress closure is valid for moderate particle Reynolds numbers, O(Re<INF>p</INF>) similar to 10.

Place, publisher, year, edition, pages
Cambridge University Press, 2018
Keywords
particle/fluid flow, rheology, suspensions
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-233414 (URN)10.1017/jfm.2018.532 (DOI)000440857700001 ()2-s2.0-85051202483 (Scopus ID)
Funder
EU, European Research Council, ERC-2013-CoG-616186
Note

QC 20180821

Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2018-08-21Bibliographically 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)000435428900016 ()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: 2018-07-02Bibliographically approved
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