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Publications (10 of 19) Show all publications
Sardina, G. (2016). An Efficient-high Performance Code for Particle Transport in Homogeneous Turbulence. In: Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2016 (ICCMSE-2016): . Paper presented at International Conference of Computational Methods in Sciences and Engineering (ICCMSE), MAR 17-20, 2016, Athens, GREECE. American Institute of Physics (AIP), Article ID UNSP 090004.
Open this publication in new window or tab >>An Efficient-high Performance Code for Particle Transport in Homogeneous Turbulence
2016 (English)In: Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2016 (ICCMSE-2016), American Institute of Physics (AIP), 2016, article id UNSP 090004Conference paper, Published paper (Refereed)
Abstract [en]

We have developed a fully parallel fortran/MPI code for tracking particles in homogeneous turbulent flows. The fluid is discretized in a uniform Eulerian grid while the particles are evolved via a Lagrangian tracking framework. The code is pseudo-spectral and employs the libraries FFTw, time integration has a third or fourth-order accuracy. The carrier phase can transport several equations for active/passive scalars that can act like a source of mass/energy transfer to the particles. We were able to simulate a fully-turbulent flow in an Eulerian grid of about 10(10) points and to track in a Lagrangian framework at least 10(9) point particles. The code is fully modular, can be easily extended or modified and available upon request.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
Series
AIP Conference Proceedings, ISSN 0094-243X ; 1790
Keywords
DNS, particle laden flows
National Category
Computer and Information Sciences Physical Sciences
Identifiers
urn:nbn:se:kth:diva-200083 (URN)10.1063/1.4968691 (DOI)000389449900057 ()2-s2.0-85008620725 (Scopus ID)978-0-7354-1454-9 (ISBN)
Conference
International Conference of Computational Methods in Sciences and Engineering (ICCMSE), MAR 17-20, 2016, Athens, GREECE
Funder
Swedish e‐Science Research Center
Note

QC 20170125

Available from: 2017-01-25 Created: 2017-01-20 Last updated: 2018-01-13Bibliographically approved
Noorani, A., Sardina, G., Brandt, L. & Schlatter, P. (2016). Particle transport in turbulent curved pipe flow. Journal of Fluid Mechanics, 793, 248-279
Open this publication in new window or tab >>Particle transport in turbulent curved pipe flow
2016 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 793, p. 248-279Article in journal (Refereed) Published
Abstract [en]

Direct numerical simulations (DNS) of particle-laden turbulent flow in straight, mildly curved and strongly bent pipes are performed in which the solid phase is modelled as small heavy spherical particles. A total of seven populations of dilute particles with different Stokes numbers, one-way coupled with their carrier phase, are simulated. The objective is to examine the effect of the curvature on micro-particle transport and accumulation. It is shown that even a slight non-zero curvature in the flow configuration strongly impact the particle concentration map such that the concentration of inertial particles with hulk Stokes number 0.45 (based on hulk velocity and pipe radius) at the inner bend wall of mildly curved pipe becomes 12.8 times larger than that in the viscous sublayer of the straight pipe. Near-wall helicoidal particle streaks are observed in the curved configurations with their inclination varying with the strength of the secondary motion of the carrier phase. A reflection layer, as previously observed in particle laden turbulent S-shaped channels, is also apparent in the strongly curved pipe with heavy particles. In addition, depending on the curvature, the central regions of the mean Dean vortices appear to he completely depleted of particles, as observed also in the partially relaminarised region at the inner bend. The turbophoretic drift of the particles is shown to he affected by weak and strong secondary motions of the carrier phase and geometry-induced centrifugal forces. The first- and second-order moments of the velocity and acceleration of the particulate phase in the same configurations are addressed in a companion paper by the same authors. The current data set will be useful for modelling particles advected in wall-bounded turbulent flows where the effects of the curvature are not negligible.

Place, publisher, year, edition, pages
Cambridge University Press, 2016
Keywords
multiphase flow, particie/fluid flow, turbulence simulation
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-185618 (URN)10.1017/jfm.2016.136 (DOI)000372822600011 ()2-s2.0-84962542958 (Scopus ID)
Note

QC 20160429

Available from: 2016-04-29 Created: 2016-04-25 Last updated: 2017-11-30Bibliographically approved
Collotta, M., De Marchis, M. & Sardina, G. (2016). Preface of the "symposium on Advanced Engineering Systems and Computer Applications: Theory and Practice". Paper presented at 17 March 2016 through 20 March 2016. AIP Conference Proceedings, 1790, Article ID 090001.
Open this publication in new window or tab >>Preface of the "symposium on Advanced Engineering Systems and Computer Applications: Theory and Practice"
2016 (English)In: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 1790, article id 090001Article in journal (Refereed) Published
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-201864 (URN)10.1063/1.4968688 (DOI)2-s2.0-85008622716 (Scopus ID)
Conference
17 March 2016 through 20 March 2016
Note

QC 20170308

Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2017-11-29Bibliographically approved
Fornari, W., Picano, F., Sardina, G. & Brandt, L. (2016). Reduced particle settling speed in turbulence. Journal of Fluid Mechanics, 808, 153-167
Open this publication in new window or tab >>Reduced particle settling speed in turbulence
2016 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 808, p. 153-167Article in journal (Refereed) Published
Abstract [en]

We study the settling of finite-size rigid spheres in sustained homogeneous isotropic turbulence (1111) by direct numerical simulations using an immersed boundary method to account for the dispersed solid phase. We study semi-dilute suspensions at different Galileo numbers, Ga. The Galileo number is the ratio between buoyancy and viscous forces, and is here varied via the solid-to-fluid density ratio rho(p)/rho(f), The focus is on particles that are slightly heavier than the fluid. We find that in HIT, the mean settling speed is less than that in quiescent fluid; in particular, it reduces by 6 %-60 % with respect to the terminal velocity of an isolated sphere in quiescent fluid as the ratio between the latter and the turbulent velocity fluctuations it is decreased. Analysing the fluid particle relative motion, we find that the mean settling speed is progressively reduced while reducing rho(p)/rho(f) due to the increase of the vertical drag induced by the particle cross-flow velocity. Unsteady effects contribute to the mean overall drag by about 6%-10%. The probability density functions of particle velocities and accelerations reveal that these are closely related to the features of the turbulent flow. The particle mean-square displacement in the settling direction is found to be similar for all Ga if time is scaled by (2a)/u' (where 2a is the particle diameter and a is the turbulence velocity root mean square).

Place, publisher, year, edition, pages
Cambridge University Press, 2016
Keywords
multiphase and particle-laden flows, particle/fluid flow, suspensions
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-198953 (URN)10.1017/jfm.2016.648 (DOI)000387140500010 ()2-s2.0-84992747372 (Scopus ID)
Funder
Swedish e‐Science Research CenterEU, European Research Council, ERC-2013-CoG-616186Swedish Research Council
Note

QC 20170113

Available from: 2017-01-13 Created: 2016-12-22 Last updated: 2017-11-29Bibliographically approved
Bäbler, M., Biferale, L., Brandt, L., Feudel, U., Guseva, K., Lanotte, A. S., . . . Toschi, F. (2015). Numerical simulations of aggregate breakup in bounded and unbounded turbulent flows. Journal of Fluid Mechanics, 766
Open this publication in new window or tab >>Numerical simulations of aggregate breakup in bounded and unbounded turbulent flows
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2015 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 766Article in journal (Refereed) Published
Abstract [en]

Breakup of small aggregates in fully developed turbulence is studied by means of direct numerical simulations in a series of typical bounded and unbounded flow configurations, such as a turbulent channel flow, a developing boundary layer and homogeneous isotropic turbulence. The simplest criterion for breakup is adopted, whereby aggregate breakup occurs when the local hydrodynamic stress sigma similar to epsilon(1/2), with epsilon being the energy dissipation at the position of the aggregate, overcomes a given threshold sigma(cr), which is characteristic for a given type of aggregate. Results show that the breakup rate decreases with increasing threshold. For small thresholds, it develops a scaling behaviour among the different flows. For high thresholds, the breakup rates show strong differences between the different flow configurations, highlighting the importance of non-universal mean-flow properties. To further assess the effects of flow inhomogeneity and turbulent fluctuations, the results are compared with those obtained in a smooth stochastic flow. Furthermore, we discuss the limitations and applicability of a set of independent proxies.

Keywords
breakup/coalescence, multiphase and particle-laden flows, turbulent flows
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:kth:diva-161602 (URN)10.1017/jfm.2015.13 (DOI)000349076900008 ()2-s2.0-84946893826 (Scopus ID)
Note

QC 20150325

Available from: 2015-03-25 Created: 2015-03-13 Last updated: 2017-12-04Bibliographically approved
Zhan, C., Sardina, G., Lushi, E. & Brandt, L. (2014). Accumulation of motile elongated micro-organisms in turbulence. Journal of Fluid Mechanics, 739, 22-36
Open this publication in new window or tab >>Accumulation of motile elongated micro-organisms in turbulence
2014 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 739, p. 22-36Article in journal (Refereed) Published
Abstract [en]

We study the effect of turbulence on marine life by performing numerical simulations of motile micro-organisms, modelled as prolate spheroids, in isotropic homogeneous turbulence. We show that the clustering and patchiness observed in laminar flows, linear shear and vortex flows, are significantly reduced in a three-dimensional turbulent flow mainly because of the complex topology; elongated micro-organisms show some level of clustering in the case of swimmers without any preferential alignment whereas spherical swimmers remain uniformly distributed. Micro-organisms with one preferential swimming direction (e.g. gyrotaxis) still show significant clustering if spherical in shape, whereas prolate swimmers remain more uniformly distributed. Due to their large sensitivity to the local shear, these elongated swimmers react more slowly to the action of vorticity and gravity and therefore do not have time to accumulate in a turbulent flow. These results show how purely hydrodynamic effects can alter the ecology of micro-organisms that can vary their shape and their preferential orientation.

Keywords
biological fluid dynamics, micro-organism dynamics
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-143737 (URN)10.1017/jfm.2013.608 (DOI)000331624200002 ()2-s2.0-84910642794 (Scopus ID)
Funder
Swedish Research CouncilSwedish e‐Science Research Center
Note

QC 20140327

Available from: 2014-03-27 Created: 2014-03-27 Last updated: 2019-05-23Bibliographically approved
Segalini, A., Bellani, G., Sardina, G., Brandt, L. & Variano, E. A. (2014). Corrections for one- and two-point statistics measured with coarse-resolution particle image velocimetry. Experiments in Fluids, 55(6), 1739
Open this publication in new window or tab >>Corrections for one- and two-point statistics measured with coarse-resolution particle image velocimetry
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2014 (English)In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 55, no 6, p. 1739-Article in journal (Refereed) Published
Abstract [en]

A theoretical model to determine the effect of the size of the interrogation window in particle image velocimetry measurements of turbulent flows is presented. The error introduced by the window size in two-point velocity statistics, including velocity autocovariance and structure functions, is derived for flows that are homogeneous within a 2D plane or 3D volume. This error model is more general than those previously discussed in the literature and provides a more direct method of correcting biases in experimental data. Within this model framework, simple polynomial approximations are proposed to provide a quick estimation of the effect of the averaging on these statistics. The error model and its polynomial approximation are validated using statistics of homogeneous isotropic turbulence obtained in a physical experiment and in a direct numerical simulation. The results demonstrate that the present formulation is able to correctly estimate the turbulence statistics, even in the case of strong smoothing due to a large interrogation window. We discuss how to use these results to correct experimental data and to aid the comparison of numerical results with laboratory data.

Keywords
Energy-Dissipation Rate, International Piv Challenge, Spatial-Resolution, Turbulent-Flow, Hot-Wire, Isotropy, 3RD
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-148309 (URN)10.1007/s00348-014-1739-z (DOI)000338322400020 ()2-s2.0-84901562406 (Scopus ID)
Note

QC 20140808

Available from: 2014-08-08 Created: 2014-08-05 Last updated: 2017-12-05Bibliographically approved
Sardina, G., Picano, F., Schlatter, P., Brandt, L. & Casciola, C. M. (2014). Statistics of Particle Accumulation in Spatially Developing Turbulent Boundary Layers. Flow Turbulence and Combustion, 92(1-2), 27-40
Open this publication in new window or tab >>Statistics of Particle Accumulation in Spatially Developing Turbulent Boundary Layers
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2014 (English)In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 92, no 1-2, p. 27-40Article in journal (Refereed) Published
Abstract [en]

We present the results of a Direct Numerical Simulation of a particle-laden spatially developing turbulent boundary layer up to Re (theta) = 2500. Two main features differentiate the behavior of inertial particles in a zero-pressure-gradient turbulent boundary layer from the more commonly studied case of a parallel channel flow. The first is the variation along the streamwise direction of the local dimensionless parameters defining the fluid-particle interactions. The second is the coexistence of an irrotational free-stream and a near-wall rotational turbulent flow. As concerns the first issue, an inner and an outer Stokes number can be defined using inner and outer flow units. The inner Stokes number governs the near-wall behavior similarly to the case of channel flow. To understand the effect of a laminar-turbulent interface, we examine the behavior of particles initially released in the free stream and show that they present a distinct behavior with respect to those directly injected inside the boundary layer. A region of minimum concentration occurs inside the turbulent boundary layer at about one displacement thickness from the wall. Its formation is due to the competition between two transport mechanisms: a relatively slow turbulent diffusion towards the buffer layer and a fast turbophoretic drift towards the wall.

Keywords
Inertial particles, Turbulent boundary layers, Wall flows, Turbophoresis, DNS
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-140126 (URN)10.1007/s10494-013-9506-4 (DOI)000328844400003 ()2-s2.0-84891835981 (Scopus ID)
Funder
Swedish e‐Science Research Center
Note

QC 20140122

Available from: 2014-01-22 Created: 2014-01-17 Last updated: 2017-12-06Bibliographically approved
Olivieri, S., Picano, F., Sardina, G., Iudicone, D. & Brandt, L. (2014). The effect of the Basset history force on particle clustering in homogeneous and isotropic turbulence. Physics of fluids, 26(4), 041704
Open this publication in new window or tab >>The effect of the Basset history force on particle clustering in homogeneous and isotropic turbulence
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2014 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 26, no 4, p. 041704-Article in journal (Refereed) Published
Abstract [en]

We study the effect of the Basset history force on the dynamics of small particles transported in homogeneous and isotropic turbulence and show that this term, often neglected in previous numerical studies, reduces the small-scale clustering typical of inertial particles. The contribution of this force to the total particle acceleration is, on average, responsible for about 10% of the total acceleration and particularly relevant during rare strong events. At moderate density ratios, i.e., sand or metal powder in water, its presence alters the balance of forces determining the particle acceleration.

Keywords
Reynolds-Number, Heavy-Particles, Flow, Velocity, Acceleration, Combustion, Simulation, Motion, Sphere
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-147066 (URN)10.1063/1.4871480 (DOI)000336152700004 ()2-s2.0-84904185291 (Scopus ID)
Funder
Swedish e‐Science Research Center
Note

QC 20140625

Available from: 2014-06-25 Created: 2014-06-23 Last updated: 2017-12-05Bibliographically approved
Gualtieri, P., Picano, F., Sardina, G. & Casciola, C. M. (2013). Clustering and turbulence modulation in particle-laden shear flows. Journal of Fluid Mechanics, 715, 134-162
Open this publication in new window or tab >>Clustering and turbulence modulation in particle-laden shear flows
2013 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 715, p. 134-162Article in journal (Refereed) Published
Abstract [en]

Turbulent fluctuations induce the common phenomenon known as clustering in the spatial arrangement of small inertial particles transported by the fluid. Particles spread non-uniformly, and form clusters where their local concentration is much higher than in nearby rarefaction regions. The underlying physics has been exhaustively analysed in the so-called one-way coupling regime, i.e. negligible back-reaction of the particles on the fluid, where the mean flow anisotropy induces preferential orientation of the clusters. Turbulent transport in suspensions with significant mass in the disperse phase, i.e. particles back-reacting in the carrier phase (the two-way coupling regime), has instead been much less investigated and is still poorly understood. The issue is discussed here by addressing direct numerical simulations of particle-laden homogeneous shear flows in the two-way coupling regime. Consistent with previous findings, we observe an overall depletion of the turbulent fluctuations for particles with response time of the order of the Kolmogorov time scale. The depletion occurs in the energy-containing range, while augmentation is observed in the small-scale range down to the dissipative scales. Increasing the mass load results in substantial broadening of the energy cospectrum, thereby extending the range of scales driven by anisotropic production mechanisms. As discussed throughout the paper, this is due to the clusters which form the spatial support of the back-reaction field and give rise to a highly anisotropic forcing, active down to the smallest scales. A certain impact on two-phase flow turbulence modelling is expected from the above conclusions, since the frequently assumed small-scale isotropy is poorly recovered when the coupling between the phases becomes significant.

Keywords
homogeneous turbulence, multiphase and particle-laden flows, turbulent flows
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-118185 (URN)10.1017/jfm.2012.503 (DOI)000313588800005 ()2-s2.0-84872174997 (Scopus ID)
Note

QC 20130214

Available from: 2013-02-14 Created: 2013-02-13 Last updated: 2017-12-06Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-9172-6311

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