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Publications (10 of 189) Show all publications
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, ISSN 1943-6947, E-ISSN 1553-0124, 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 ()
Note

QC 20190215

Available from: 2019-02-09 Created: 2019-02-09 Last updated: 2019-02-22Bibliographically approved
Zhan, C., Hagrot, E., Brandt, L. & Chotteau, V. (2019). Study of hydrodynamics in wave bioreactors by computational fluid dynamics reveals a resonance phenomenon. Chemical Engineering Science, 193, 53-65
Open this publication in new window or tab >>Study of hydrodynamics in wave bioreactors by computational fluid dynamics reveals a resonance phenomenon
2019 (English)In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 193, p. 53-65Article in journal (Refereed) Published
Abstract [en]

Culture of mammalian or human cells in Wave bioreactor is widely used for cell expansion or for biologics manufacturing. Wave bioreactor cultivation of sensitive cells such as stem cells, immune cells or anchorage-dependent cells, is recognized as an attractive option for culture in suspension or adherently on microcarriers. A systematic optimization of the mixing, oxygen transfer rate and shear stress, most favorable for the cells requires a deep understanding of the hydrodynamics inside the Wave bioreactor bag, i.e. cellbag. Numerical simulation by Computation Fluid Dynamics (CFD), is considered as an inexpensive and efficient tool for predicting the fluid behavior in many fields. In the present study, we perform numerical simulations by Ansys-FLUENT to characterize the flow conditions in a 10 L cellbag. The numerical simulations are carried out to investigate the fluid structures for nine different operating conditions of rocking speed and angle. The influence of these operating parameters on the mixing and the shear stress induced by the liquid motion are studied. We find that the mixing and shear stress increase with the cellbag angle from 4 degrees to 7 degrees but that increasing rocking speeds are not systematically associated with increasing mixing and shear stress. It is concluded that a resonance phenomenon is responsible for the fact that the lowest studied rocking speed, 15 rpm, generates the highest fluid velocity, mixing and shear stress compared to the higher speeds of 22 and 30 rpm.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Wave bioreactor, Computation Fluid Dynamics (CFD), Volume of fluid (VOF), Hydrodynamic, Resonance
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-238103 (URN)10.1016/j.ces.2018.08.017 (DOI)000447171800006 ()2-s2.0-85052913142 (Scopus ID)
Note

QC 20190111

Available from: 2019-01-11 Created: 2019-01-11 Last updated: 2019-01-11Bibliographically approved
Zade, S., Lundell, F. & Brandt, L. (2019). Turbulence modulation by finite-size spherical particles in Newtonian and viscoelastic fluids. International Journal of Multiphase Flow, 112, 116-129
Open this publication in new window or tab >>Turbulence modulation by finite-size spherical particles in Newtonian and viscoelastic fluids
2019 (English)In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 112, p. 116-129Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-243840 (URN)10.1016/j.ijmultiphaseflow.2018.12.015 (DOI)2-s2.0-85058816573 (Scopus ID)
Note

QC 20190215

Available from: 2019-02-07 Created: 2019-02-07 Last updated: 2019-02-15Bibliographically approved
Shahmardi, A., Zade, S., Niazi Ardekani, M., Poole, R. J., Lundell, F., Rosti, M. E. & Brandt, L. (2019). Turbulent duct flow with polymers. Journal of Fluid Mechanics, 859, 1057-1083
Open this publication in new window or tab >>Turbulent duct flow with polymers
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2019 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 859, p. 1057-1083Article in journal (Refereed) Published
Abstract [en]

We have performed direct numerical simulation of the turbulent flow of a polymer solution in a square duct, with the FENE-P model used to simulate the presence of polymers. First, a simulation at a fixed moderate Reynolds number is performed and its results compared with those of a Newtonian fluid to understand the mechanism of drag reduction and how the secondary motion, typical of the turbulent flow in non-axisymmetric ducts, is affected by polymer additives. Our study shows that the Prandtl's secondary flow is modified by the polymers: the circulation of the streamwise main vortices increases and the location of the maximum vorticity moves towards the centre of the duct. In-plane fluctuations are reduced while the streamwise ones are enhanced in the centre of the duct and dumped in the corners due to a substantial modification of the quasi-streamwise vortices and the associated near-wall low- and high-speed streaks; these grow in size and depart from the walls, their streamwise coherence increasing. Finally, we investigated the effect of the parameters defining the viscoelastic behaviour of the flow and found that the Weissenberg number strongly influences the flow, with the cross-stream vortical structures growing in size and the in-plane velocity fluctuations reducing for increasing flow elasticity.We have performed direct numerical simulation of the turbulent flow of a polymer solution in a square duct, with the FENE-P model used to simulate the presence of polymers. First, a simulation at a fixed moderate Reynolds number is performed and its results compared with those of a Newtonian fluid to understand the mechanism of drag reduction and how the secondary motion, typical of the turbulent flow in non-axisymmetric ducts, is affected by polymer additives. Our study shows that the Prandtl's secondary flow is modified by the polymers: the circulation of the streamwise main vortices increases and the location of the maximum vorticity moves towards the centre of the duct. In-plane fluctuations are reduced while the streamwise ones are enhanced in the centre of the duct and dumped in the corners due to a substantial modification of the quasi-streamwise vortices and the associated near-wall low- and high-speed streaks; these grow in size and depart from the walls, their streamwise coherence increasing. Finally, we investigated the effect of the parameters defining the viscoelastic behaviour of the flow and found that the Weissenberg number strongly influences the flow, with the cross-stream vortical structures growing in size and the in-plane velocity fluctuations reducing for increasing flow elasticity.

Place, publisher, year, edition, pages
Cambridge University Press, 2019
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-240129 (URN)10.1017/jfm.2018.858 (DOI)000451519800001 ()2-s2.0-85057589811 (Scopus ID)
Funder
Swedish Research Council, 2014-5001EU, European Research Council, ERC-2013-CoG-616186Swedish e‐Science Research Center
Note

QC 20181213

Available from: 2018-12-12 Created: 2018-12-12 Last updated: 2018-12-13Bibliographically approved
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: 2018-12-12Bibliographically approved
Izbassarov, D., Rosti, M. E., Niazi Ardekani, M., Sarabian, M., Hormozi, S., Brandt, L. & Tammisola, O. (2018). Computational modeling of multiphase viscoelastic and elastoviscoplastic flows. International Journal for Numerical Methods in Fluids, 521-543
Open this publication in new window or tab >>Computational modeling of multiphase viscoelastic and elastoviscoplastic flows
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2018 (English)In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, p. 521-543Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2018
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-240127 (URN)10.1002/fld.4678 (DOI)000450028200001 ()2-s2.0-85052317831 (Scopus ID)
Funder
Swedish Research Council, VR 2014-5001Swedish Research Council, VR2017-4809Swedish Research Council, VR2013-5789
Note

QC 20181214

Available from: 2018-12-12 Created: 2018-12-12 Last updated: 2018-12-14Bibliographically approved
Izbassarov, D., Rosti, M. E., Niazi Ardekani, M., Sarabian, M., Hormozi, S., Brandt, L. & Tammisola, O. (2018). Computational modeling of multiphase viscoelastic and elastoviscoplastic flows. International Journal for Numerical Methods in Fluids, 88(12), 521-543
Open this publication in new window or tab >>Computational modeling of multiphase viscoelastic and elastoviscoplastic flows
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2018 (English)In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 88, no 12, p. 521-543Article in journal (Refereed) Published
Abstract [en]

In this paper, a three-dimensional numerical solver is developed for suspensions of rigid and soft particles and droplets in viscoelastic and elastoviscoplastic (EVP) fluids. The presented algorithm is designed to allow for the first time three-dimensional simulations of inertial and turbulent EVP fluids with a large number particles and droplets. This is achieved by combining fast and highly scalable methods such as an FFT-based pressure solver, with the evolution equation for non-Newtonian (including EVP) stresses. In this flexible computational framework, the fluid can be modeled by either Oldroyd-B, neo-Hookean, FENE-P, or Saramito EVP models, and the additional equations for the non-Newtonian stresses are fully coupled with the flow. The rigid particles are discretized on a moving Lagrangian grid, whereas the flow equations are solved on a fixed Eulerian grid. The solid particles are represented by an immersed boundary method with a computationally efficient direct forcing method, allowing simulations of a large numbers of particles. The immersed boundary force is computed at the particle surface and then included in the momentum equations as a body force. The droplets and soft particles on the other hand are simulated in a fully Eulerian framework, the former with a level-set method to capture the moving interface and the latter with an indicator function. The solver is first validated for various benchmark single-phase and two-phase EVP flow problems through comparison with data from the literature. Finally, we present new results on the dynamics of a buoyancy-driven drop in an EVP fluid.

Place, publisher, year, edition, pages
WILEY, 2018
Keywords
elastoviscoplastic multiphase systems, FENE-P model, immersed boundary method, level-set method, Oldroyd-B model, Saramito model
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-239748 (URN)10.1002/fld.4678 (DOI)000450028200001 ()2-s2.0-85052317831 (Scopus ID)
Note

QC 20190110

Available from: 2019-01-10 Created: 2019-01-10 Last updated: 2019-01-10Bibliographically 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
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