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Costa, P., Brandt, L. & Picano, F. (2020). Interface-resolved simulations of small inertial particles in turbulent channel flow. Journal of Fluid Mechanics, 883, Article ID A54.
Open this publication in new window or tab >>Interface-resolved simulations of small inertial particles in turbulent channel flow
2020 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 883, article id A54Article in journal (Refereed) Published
Abstract [en]

We present a direct comparison between interface-resolved and one-way-coupled point-particle direct numerical simulations (DNS) of gravity-free turbulent channel flow laden with small inertial particles, with high particle-to-fluid density ratio and diameter of approximately three viscous units. The most dilute flow considered, solid volume fraction O(10(-5)), shows the particle feedback on the flow to be negligible, whereas differences with respect to the unladen case, notably a drag increase of approximately 10 %, are found for a volume fraction O(10(-4)). This is attributed to a dense layer of particles at the wall, caused by turbophoresis, flowing with large particle-to-fluid apparent slip velocity. The most dilute case is therefore taken as the benchmark for assessing the validity of a widely used point-particle model, where the particle dynamics results only from inertial and nonlinear drag forces. In the bulk of the channel, the first- and second-order moments of the particle velocity from the point-particle DNS agree well with those from the interface-resolved DNS. Close to the wall, however, most of the statistics show major qualitative differences. We show that this difference originates from the strong shear-induced lift force acting on the particles in the near-wall region. This mechanism is well captured by the lift force model due to Saffman (J. Fluid Mech., vol. 22 (2), 1965, pp. 385-400), while other widely used, more elaborate, approaches aiming at extending the lift model for a wider range of particle Reynolds numbers can actually underpredict the magnitude of the near-wall particle velocity fluctuations for the cases analysed here.

Place, publisher, year, edition, pages
Cambridge University Press, 2020
Keywords
multiphase flow, particle, fluid flows
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-265513 (URN)10.1017/jfm.2019.918 (DOI)000499724600001 ()2-s2.0-85075801940 (Scopus ID)
Note

QC 20191213

Available from: 2019-12-13 Created: 2019-12-13 Last updated: 2020-01-08Bibliographically approved
Lupo, G., Niazi Ardekani, M., Brandt, L. & Duwig, C. (2019). An Immersed Boundary Method for flows with evaporating droplets. International Journal of Heat and Mass Transfer, 143, Article ID 118563.
Open this publication in new window or tab >>An Immersed Boundary Method for flows with evaporating droplets
2019 (English)In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 143, article id 118563Article in journal (Refereed) Published
Abstract [en]

We present a new Immersed Boundary Method (IBM) for the interface resolved simulation of spherical droplet evaporation in gas flow. The method is based on the direct numerical simulation of the coupled momentum, energy and species transport in the gas phase, while the exchange of these quantities with the liquid phase is handled through global mass, energy and momentum balances for each droplet. This approach, applicable in the limit of small spherical droplets, allows for accurate and efficient phase coupling without direct solution of the liquid phase fields, thus saving computational cost. We provide validation results, showing that all the relevant physical phenomena and their interactions are correctly captured, both for laminar and turbulent gas flow. Test cases include fixed rate and free evaporation of a static droplet, displacement of a droplet by Stefan flow, and evaporation of a hydrocarbon droplet in homogeneous isotropic turbulence. The latter case is validated against experimental data, showing the feasibility of the method towards the treatment of conditions representative of real life spray fuel applications.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Spray, Fuel, Evaporation, Phase change, Immersed boundary, Multiphase, Direct numerical simulation
National Category
Engineering and Technology
Research subject
Computer Science
Identifiers
urn:nbn:se:kth:diva-261933 (URN)10.1016/j.ijheatmasstransfer.2019.118563 (DOI)000487564400090 ()2-s2.0-85070927066 (Scopus ID)
Note

QC 20191015

Available from: 2019-10-15 Created: 2019-10-15 Last updated: 2019-11-26Bibliographically approved
Zade, S., Fornari, W., Lundell, F. & Brandt, L. (2019). Buoyant finite-size particles in turbulent duct flow. Physical Review Fluids (4), Article ID 024303.
Open this publication in new window or tab >>Buoyant finite-size particles in turbulent duct flow
2019 (English)In: Physical Review Fluids, E-ISSN 2469-990X, no 4, article id 024303Article in journal (Refereed) Published
Abstract [en]

Particle image velocimetry and particle tracking velocimetry have been employed to investigate the dynamics of finite-size spherical particles, slightly heavier than the carrier fluid, in a horizontal turbulent square duct flow. Interface resolved direct numerical simulations (DNSs) have also been performed with the immersed boundary method at the same experimental conditions, bulk Reynolds number Re2H=5600, duct height to particle-size ratio 2H/dp=14.5, particle volume fraction Φ=1%, and particle to fluid density ratio ρp/ρf=1.0035. Good agreement has been observed between experiments and simulations in terms of the overall pressure drop, concentration distribution, and turbulent statistics of the two phases. Additional experimental results considering two particle sizes 2H/dp=14.5 and 9 and multiple Φ=1%, 2%, 3%, 4%, and 5% are reported at the same Re2H. The pressure drop monotonically increases with the volume fraction, almost linearly and nearly independently of the particle size for the above parameters. However, despite the similar pressure drop, the microscopic picture in terms of fluid velocity statistics differs significantly with the particle size. This one-to-one comparison between simulations and experiments extends the validity of interface resolved DNS in complex turbulent multiphase flows and highlights the ability of experiments to investigate such flows in considerable detail, even in regions where the local volume fraction is relatively high.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-243895 (URN)10.1103/PhysRevFluids.4.024303 (DOI)000458160100003 ()2-s2.0-85062418601 (Scopus ID)
Note

QC 20190215

Available from: 2019-02-09 Created: 2019-02-09 Last updated: 2019-09-03Bibliographically approved
Rosti, M. E., Ge, Z., Jain, S. S., Dodd, M. S. & Brandt, L. (2019). Droplets in homogeneous shear turbulence. Journal of Fluid Mechanics, 876, 962-984
Open this publication in new window or tab >>Droplets in homogeneous shear turbulence
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2019 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 876, p. 962-984Article in journal (Refereed) Published
Abstract [en]

We simulate the flow of two immiscible and incompressible fluids separated by an interface in a homogeneous turbulent shear flow at a shear Reynolds number equal to 15 200. The viscosity and density of the two fluids are equal, and various surface tensions and initial droplet diameters are considered in the present study. We show that the two-phase flow reaches a statistically stationary turbulent state sustained by a non-zero mean turbulent production rate due to the presence of the mean shear. Compared to single-phase flow, we find that the resulting steady-state conditions exhibit reduced Taylor-microscale Reynolds numbers owing to the presence of the dispersed phase, which acts as a sink of turbulent kinetic energy for the carrier fluid. At steady state, the mean power of surface tension is zero and the turbulent production rate is in balance with the turbulent dissipation rate, with their values being larger than in the reference single-phase case. The interface modifies the energy spectrum by introducing energy at small scales, with the difference from the single-phase case reducing as the Weber number increases. This is caused by both the number of droplets in the domain and the total surface area increasing monotonically with the Weber number. This reflects also in the droplet size distribution, which changes with the Weber number, with the peak of the distribution moving to smaller sizes as the Weber number increases. We show that the Hinze estimate for the maximum droplet size, obtained considering break-up in homogeneous isotropic turbulence, provides an excellent estimate notwithstanding the action of significant coalescence and the presence of a mean shear.

Place, publisher, year, edition, pages
Cambridge University Press, 2019
Keywords
drops, multiphase flow, turbulence simulation
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-257426 (URN)10.1017/jfm.2019.581 (DOI)000480242100001 ()2-s2.0-85070481433 (Scopus ID)
Note

QC 20190902

Available from: 2019-09-02 Created: 2019-09-02 Last updated: 2019-09-02Bibliographically approved
Rosti, M. E., Niazi Ardekani, M. & Brandt, L. (2019). Effect of elastic walls on suspension flow. Physical Review Fluids, 4(6), Article ID 062301.
Open this publication in new window or tab >>Effect of elastic walls on suspension flow
2019 (English)In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 4, no 6, article id 062301Article in journal (Refereed) Published
Abstract [en]

We study suspensions of rigid particles in a plane Couette flow with deformable elastic walls. We find that, in the limit of vanishing inertia, the elastic walls induce shear thinning of the suspension flow such that the effective viscosity decreases as the wall deformability increases. This shear-thinning behavior originates from the interactions between rigid particles, soft walls, and carrier fluids; an asymmetric wall deformation induces a net lift force acting on the particles which therefore migrate towards the bulk of the channel. Based on our observations, we provide a closure for the suspension viscosity which can be used to model the rheology of suspensions with arbitrary volume fraction in elastic channels.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-255317 (URN)10.1103/PhysRevFluids.4.062301 (DOI)000473044100001 ()2-s2.0-85069716507 (Scopus ID)
Note

QC 20190805

Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-05Bibliographically approved
Ge, Z., Tammisola, O. & Brandt, L. (2019). Flow-assisted droplet assembly in a 3D microfluidic channel. Soft Matter, 15(16), 3451-3460
Open this publication in new window or tab >>Flow-assisted droplet assembly in a 3D microfluidic channel
2019 (English)In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 15, no 16, p. 3451-3460Article in journal (Refereed) Published
Abstract [en]

Self-assembly of soft matter, such as droplets or colloids, has become a promising scheme to engineer novel materials, model living matter, and explore non-equilibrium statistical mechanics. In this article, we present detailed numerical simulations of few non-Brownian droplets in various flow conditions, specifically, focusing on their self-assembly within a short distance in a three-dimensional (3D) microfluidic channel, cf. [Shen et al., Adv. Sci., 2016, 3(6), 1600012]. Contrary to quasi two-dimensional (q2D) systems, where dipolar interaction is the key mechanism for droplet rearrangement, droplets in 3D confinement produce much less disturbance to the underlying flow, thus experiencing weaker dipolar interactions. Using confined simple shear and Poiseuille flows as reference flows, we show that the droplet dynamics is mostly affected by the shear-induced cross-stream migration, which favors chain structures if the droplets are under an attractive depletion force. For more compact clusters, such as three droplets in a triangular shape, our results suggest that an inhomogeneous cross-sectional inflow profile is further required. Overall, the accelerated self-assembly of a small-size droplet cluster results from the combined effects of strong depletion forces, confinement-mediated shear alignments, and fine-tuned inflow conditions. The deterministic nature of the flow-assisted self-assembly implies the possibility of large throughputs, though calibration of all different effects to directly produce large droplet crystals is generally difficult.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-252637 (URN)10.1039/c8sm02479k (DOI)000468007600014 ()30958490 (PubMedID)2-s2.0-85064601819 (Scopus ID)
Note

QC 20190610

Available from: 2019-06-10 Created: 2019-06-10 Last updated: 2019-06-10Bibliographically approved
Rosti, M. E., Olivieri, S., Banaei, A. A., Brandt, L. & Mazzino, A. (2019). Flowing fibers as a proxy of turbulence statistics. Meccanica (Milano. Print)
Open this publication in new window or tab >>Flowing fibers as a proxy of turbulence statistics
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2019 (English)In: Meccanica (Milano. Print), ISSN 0025-6455, E-ISSN 1572-9648Article in journal (Refereed) Published
Abstract [en]

The flapping states of a flexible fiber fully coupled to a three-dimensional turbulent flow are investigated via state-of-the-art numerical methods. Two distinct flapping regimes are predicted by the phenomenological theory recently proposed by Rosti et al. (Phys. Rev. Lett. 121:044501, 2018) the under-damped regime, where the elasticity strongly affects the fiber dynamics, and the over-damped regime, where the elastic effects are strongly inhibited. In both cases we can identify a critical value of the bending rigidity of the fiber by a resonance condition, which further provides a distinction between different flapping behaviors, especially in the under-damped case. We validate the theory by means of direct numerical simulations and find that, both for the over-damped regime and for the under-damped one, fibers are effectively slaved to the turbulent fluctuations and can therefore be used as a proxy to measure various two-point statistics of turbulence. Finally, we show that this holds true also in the case of a passive fiber, without any feedback force on the fluid.

Place, publisher, year, edition, pages
Springer Netherlands, 2019
Keywords
Dispersed flows, Fiber, Multiphase flows, Turbulence, Multiphase flow, Numerical methods, Dispersed flow, Flapping behavior, Phenomenological theory, Resonance condition, Three-dimensional turbulent flow, Turbulence statistics, Turbulent fluctuation, Two point statistics, Fibers
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-263285 (URN)10.1007/s11012-019-00997-2 (DOI)2-s2.0-85068170932 (Scopus ID)
Note

QC 20191105

Available from: 2019-11-05 Created: 2019-11-05 Last updated: 2020-01-09Bibliographically approved
Takeishi, N., Rosti, M. E., Imai, Y., Wada, S. & Brandt, L. (2019). Haemorheology in dilute, semi-dilute and dense suspensions of red blood cells. Journal of Fluid Mechanics, 872, 818-848
Open this publication in new window or tab >>Haemorheology in dilute, semi-dilute and dense suspensions of red blood cells
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2019 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 872, p. 818-848Article in journal (Refereed) Published
Abstract [en]

We present a numerical analysis of the rheology of a suspension of red blood cells (RBCs) in a wall-bounded shear flow. The flow is assumed as almost inertialess. The suspension of RBCs, modelled as biconcave capsules whose membrane follows the Skalak constitutive law, is simulated for a wide range of viscosity ratios between the cytoplasm and plasma, D 0 : 1-10, for volume fractions up to D 0 : 41 and for different capillary numbers (Ca). Our numerical results show that an RBC at low Ca tends to orient to the shear plane and exhibits so-called rolling motion, a stable mode with higher intrinsic viscosity than the so-called tumbling motion. As Ca increases, the mode shifts from the rolling to the swinging motion. Hydrodynamic interactions (higher volume fraction) also allow RBCs to exhibit tumbling or swinging motions resulting in a drop of the intrinsic viscosity for dilute and semi-dilute suspensions. Because of this mode change, conventional ways of modelling the relative viscosity as a polynomial function of cannot be simply applied in suspensions of RBCs at low volume fractions. The relative viscosity for high volume fractions, however, can be well described as a function of an effective volume fraction, defined by the volume of spheres of radius equal to the semi-middle axis of a deformed RBC. We find that the relative viscosity successfully collapses on a single nonlinear curve independently of except for the case with Ca > 0 : 4, where the fit works only in the case of low/ moderate volume fraction, and fails in the case of a fully dense suspension.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2019
Keywords
blood flow, capsule/cell dynamics, suspensions
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-255171 (URN)10.1017/jfm.2019.393 (DOI)000471976300003 ()2-s2.0-85072027261 (Scopus ID)
Note

QC 20190904

Available from: 2019-09-04 Created: 2019-09-04 Last updated: 2019-10-04Bibliographically approved
Alghalibi, D., Rosti, M. E. & Brandt, L. (2019). Inertial migration of a deformable particle in pipe flow. Physical Review Fluids, 4(10), Article ID 104201.
Open this publication in new window or tab >>Inertial migration of a deformable particle in pipe flow
2019 (English)In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 4, no 10, article id 104201Article in journal (Refereed) Published
Abstract [en]

We perform fully Eulerian numerical simulations of an initially spherical hyperelastic particle suspended in a Newtonian pressure-driven flow in a cylindrical straight pipe. We study the full particle migration and deformation for different Reynolds numbers and for various levels of particle elasticity, to disentangle the interplay of inertia and elasticity on the particle focusing. We observe that the particle deforms and undergoes a lateral displacement while traveling downstream through the pipe, finally focusing at the pipe centerline. We note that the migration dynamics and the final equilibrium position are almost independent of the Reynolds number, while they strongly depend on the particle elasticity; in particular, the migration is faster as the elasticity increases (i.e., the particle is more deformable), with the particle reaching the final equilibrium position at the centerline in shorter times. Our simulations show that the results are not affected by the particle initial conditions, position, and velocity. Finally, we explain the particle migration by computing the total force acting on the particle and its different components, viscous and elastic.

Place, publisher, year, edition, pages
American Physical Society, 2019
Keywords
deformable particle, hyper-elastic
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-263656 (URN)10.1103/PhysRevFluids.4.104201 (DOI)000489589700003 ()2-s2.0-85074434642 (Scopus ID)
Funder
EU, European Research Council, ERC-2013-CoG-616186
Note

QC 20191115

Available from: 2019-11-07 Created: 2019-11-07 Last updated: 2019-11-15Bibliographically approved
Ghosh, S., Loiseau, J.-C., Breugem, W.-P. & Brandt, L. (2019). Modal and non-modal linear stability of Poiseuille flow through a channel with a porous substrate. European journal of mechanics. B, Fluids, 75, 29-43
Open this publication in new window or tab >>Modal and non-modal linear stability of Poiseuille flow through a channel with a porous substrate
2019 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 75, p. 29-43Article in journal (Refereed) Published
Abstract [en]

We present modal and non-modal linear stability analyses of Poiseuille flow through a plane channel with a porous substrate modeled using the Volume Averaged Navier-Stokes (VANS) equations. Modal stability analysis shows the destabilization of the flow with increasing porosity of the layer. The instability mode originates from the homogeneous fluid region of the channel for all the values of porosity considered but the governing mechanism changes. Perturbation kinetic energy analysis reveals the importance of viscous dissipation at low porosity values while dissipation in the porous substrate becomes significant at higher porosity. Scaling analysis highlights the invariance of the critical wavenumber with changing porosity. On the other hand, the critical Reynolds number remains invariant at low porosity and scales as Re-c similar to (H/delta)(1.4) at high porosity where delta is the typical thickness of the vorticity layer at the fluid-porous interface. This reveals the existence of a Tollmien-Schlichting-like viscous instability mechanism at low porosity values, and Rayleigh analysis shows the presence of an inviscid instability mechanism at high porosity. For the whole range of porosities considered, the non-modal analysis shows that the optimal mechanism responsible for transient energy amplification is the lift-up effect, giving rise to streaky structure as in single-phase plane Poiseuille flow. The present results strongly suggest that the transition to turbulence follows the same path as that of classical Poiseuille flow at low porosity values, while it is dictated by the modal instability for high porosity values. SAS. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Porous channel flow, Instability
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-245884 (URN)10.1016/j.euromechflu.2018.11.013 (DOI)000458710700003 ()2-s2.0-85059321599 (Scopus ID)
Note

QC 20180311

Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-11Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-4346-4732

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