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Pandey, V., Perlekar, P. & Mitra, D. (2019). Clustering and energy spectra in two-dimensional dusty gas turbulence. Physical review. E, 100(1), Article ID 013114.
Open this publication in new window or tab >>Clustering and energy spectra in two-dimensional dusty gas turbulence
2019 (English)In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 100, no 1, article id 013114Article in journal (Refereed) Published
Abstract [en]

We present direct numerical simulation of heavy inertial particles (dust) immersed in two-dimensional turbulent flow (gas). The dust particles are modeled as monodispersed heavy particles capable of modifying the flow through two-way coupling. By varying the Stokes number (St) and the mass-loading parameter (φm), we study the clustering phenomenon and the gas phase kinetic energy spectra. We find that the dust-dust correlation dimension (d2) also depends on φm. In particular, clustering decreases as mass loading (φm) is increased. In the kinetic energy spectra of gas we show (i) the emergence of a different scaling regime and that (ii) the scaling exponent in this regime is not universal but a function of both St and φm. Using a scale-by-scale enstrophy budget analysis we show that in this emerged scaling regime, which we call the dust-dissipative range, viscous dissipation due to the gas balances the back-reaction from the dust.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-262563 (URN)10.1103/PhysRevE.100.013114 (DOI)000477911900010 ()31499820 (PubMedID)2-s2.0-85070093114 (Scopus ID)
Note

QC 20191017

Available from: 2019-10-17 Created: 2019-10-17 Last updated: 2019-10-17Bibliographically approved
Afonso, M. M., Mitra, D. & Vincenzi, D. (2019). Kazantsev dynamo in turbulent compressible flows. Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, 475(2223), Article ID 20180591.
Open this publication in new window or tab >>Kazantsev dynamo in turbulent compressible flows
2019 (English)In: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 475, no 2223, article id 20180591Article in journal (Refereed) Published
Abstract [en]

We consider the kinematic fluctuation dynamo problem in a flow that is random, white-in-time, with both solenoidal and potential components. This model is a generalization of the well-studied Kazantsev model. If both the solenoidal and potential parts have the same scaling exponent, then, as the compressibility of the flow increases, the growth rate decreases but remains positive. If the scaling exponents for the solenoidal and potential parts differ, in particular if they correspond to typical Kolmogorov and Burgers values, we again find that an increase in compressibility slows down the growth rate but does not turn it off. The slow down is, however, weaker and the critical magnetic Reynolds number is lower than when both the solenoidal and potential components display the Kolmogorov scaling. Intriguingly, we find that there exist cases, when the potential part is smoother than the solenoidal part, for which an increase in compressibility increases the growth rate. We also find that the critical value of the scaling exponent above which a dynamo is seen is unity irrespective of the compressibility. Finally, we realize that the dimension d = 3 is special, as for all other values of d the critical exponent is higher and depends on the compressibility.

Place, publisher, year, edition, pages
ROYAL SOC, 2019
Keywords
dynamo theory, compressible turbulence, Kazantsev model
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-252411 (URN)10.1098/rspa.2018.0591 (DOI)000465427200010 ()31007546 (PubMedID)2-s2.0-85064244183 (Scopus ID)
Note

QC 20190716

Available from: 2019-07-16 Created: 2019-07-16 Last updated: 2019-07-19Bibliographically approved
Bhatnagar, A., Gupta, A., Mitra, D. & Pandit, R. (2018). Heavy inertial particles in turbulent flows gain energy slowly but lose it rapidly. Physical review. E, 97(3), Article ID 033102.
Open this publication in new window or tab >>Heavy inertial particles in turbulent flows gain energy slowly but lose it rapidly
2018 (English)In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 3, article id 033102Article in journal (Refereed) Published
Abstract [en]

We present an extensive numerical study of the time irreversibility of the dynamics of heavy inertial particles in three-dimensional, statistically homogeneous, and isotropic turbulent flows. We show that the probability density function (PDF) of the increment, W(tau), of a particle's energy over a time scale tau is non-Gaussian, and skewed toward negative values. This implies that, on average, particles gain energy over a period of time that is longer than the duration over which they lose energy. We call this slow gain and fast loss. We find that the third moment of W(tau) scales as tau(3) for small values of tau. We show that the PDF of power-input p is negatively skewed too; we use this skewness Ir as a measure of the time irreversibility and we demonstrate that it increases sharply with the Stokes number St for small St; this increase slows down at St similar or equal to 1. Furthermore, we obtain the PDFs of t(+) and t(-), the times over which p has, respectively, positive or negative signs, i.e., the particle gains or loses energy. We obtain from these PDFs a direct and natural quantification of the slow gain and fast loss of the energy of the particles, because these PDFs possess exponential tails from which we infer the characteristic loss and gain times t(loss) and t(gain), respectively, and we obtain t(loss) < t(gain) for all the cases we have considered. Finally, we show that the fast loss of energy occurs with greater probability in the strain-dominated region than in the vortical one; in contrast, the slow gain in the energy of the particles is equally likely in vortical or strain-dominated regions of the flow.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-224681 (URN)10.1103/PhysRevE.97.033102 (DOI)000426527300010 ()2-s2.0-85044138699 (Scopus ID)
Funder
Swedish Research Council, 2011-542 638-2013-9243Knut and Alice Wallenberg Foundation, KAW 2014.0048
Note

QC 20180322

Available from: 2018-03-22 Created: 2018-03-22 Last updated: 2018-03-22Bibliographically approved
Bhatnagar, A., Gustavsson, K., Mehlig, B. & Mitra, D. (2018). Relative velocities in bidisperse turbulent aerosols: Simulations and theory. Physical review. E, 98(6), Article ID 063107.
Open this publication in new window or tab >>Relative velocities in bidisperse turbulent aerosols: Simulations and theory
2018 (English)In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 6, article id 063107Article in journal (Refereed) Published
Abstract [en]

We perform direct numerical simulations of a bidisperse suspension of heavy spherical particles in forced, homogeneous, and isotropic three-dimensional turbulence. We compute the joint distribution of relative particle distances and longitudinal relative velocities between particles of different inertia. For a pair of particles with small difference in their inertias we compare our results with recent theoretical predictions [Meibohm et al., Phys. Rev. E 96, 061102 (2017)] for the shape of this distribution. We also compute the moments of relative velocities as a function of particle separation and compare with the theoretical predictions. We observe good agreement. For a pair of particles that are very different from each other-one is heavy and the other one has negligible inertia-we give a theory to calculate their root-mean-square relative velocity. This theory also agrees well with the results of our simulations.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-240719 (URN)10.1103/PhysRevE.98.063107 (DOI)000452954300002 ()2-s2.0-85058651212 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, KAW 2014.0048Swedish Research Council, 2013-3992 2017-03865Swedish Research Council Formas, 2014-585
Note

QC 20190108

Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2019-01-08Bibliographically approved
Rosti, M. E., Brandt, L. & Mitra, D. (2018). Rheology of suspensions of viscoelastic spheres: Deformability as an effective volume fraction. Physical Review Fluids, 3(1), Article ID 012301.
Open this publication in new window or tab >>Rheology of suspensions of viscoelastic spheres: Deformability as an effective volume fraction
2018 (English)In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 3, no 1, article id 012301Article in journal (Refereed) Published
Abstract [en]

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

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

QC 20180228

Available from: 2018-02-28 Created: 2018-02-28 Last updated: 2019-04-04Bibliographically approved
Bhatnagar, A., Gustavsson, K. & Mitra, D. (2018). Statistics of the relative velocity of particles in turbulent flows: Monodisperse particles. Physical review. E, 97(2), Article ID 023105.
Open this publication in new window or tab >>Statistics of the relative velocity of particles in turbulent flows: Monodisperse particles
2018 (English)In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 2, article id 023105Article in journal (Refereed) Published
Abstract [en]

We use direct numerical simulations to calculate the joint probability density function of the relative distance R and relative radial velocity component V-R for a pair of heavy inertial particles suspended in homogeneous and isotropic turbulent flows. At small scales the distribution is scale invariant, with a scaling exponent that is related to the particle-particle correlation dimension in phase space, D-2. It was argued [K. Gustavsson and B. Mehlig, Phys. Rev. E 84, 045304 (2011); J. Turbul. 15, 34 (2014)] that the scale invariant part of the distribution has two asymptotic regimes: (1) vertical bar V-R vertical bar << R, where the distribution depends solely on R, and (2) vertical bar V-R vertical bar >> R, where the distribution is a function of vertical bar V-R vertical bar alone. The probability distributions in these two regimes are matched along a straight line: vertical bar V-R vertical bar = z*R. Our simulations confirm that this is indeed correct. We further obtain D-2 and z* as a function of the Stokes number, St. The former depends nonmonotonically on St with aminimum at about St approximate to 0.7 and the latter has only a weak dependence on St.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-223788 (URN)10.1103/PhysRevE.97.023105 (DOI)000425094300011 ()2-s2.0-85042167026 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, KAW 2014.0048
Note

QC 20180307

Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-03-07Bibliographically approved
Haugen, N. E., Kruger, J., Mitra, D. & Lovas, T. (2018). The effect of turbulence on mass transfer rates of small inertial particles with surface reactions. Journal of Fluid Mechanics, 836, 932-951
Open this publication in new window or tab >>The effect of turbulence on mass transfer rates of small inertial particles with surface reactions
2018 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 836, p. 932-951Article in journal (Refereed) Published
Abstract [en]

The effect of turbulence on the mass transfer between a fluid and embedded small heavy inertial particles that experience surface reactions is studied. For simplicity, the surface reaction, which takes place when a gas phase reactant is converted to a gas phase product at the external surface of the particles, is unimolar and isothermal. Two effects are identified. The first effect is due to the relative velocity between the fluid and the particles, and a model for the relative velocity is presented. The second effect is due to the clustering of particles, where the mass transfer rate is inhibited due to the rapid depletion of the consumed species inside the dense particle clusters. This last effect is relevant for large Damkohler numbers, where the Damkohler number is defined as the ratio of the turbulent and chemical time scales, and it may totally control the mass transfer rate for Damkohler numbers larger than unity. A model that describes how this effect should be incorporated into existing simulation tools that utilize the Reynolds averaged Navier-Stokes approach is presented.

Place, publisher, year, edition, pages
Cambridge University Press, 2018
Keywords
isotropic turbulence, multiphase and particle-laden flows, turbulent reacting flows
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-240179 (URN)10.1017/jfm.2017.820 (DOI)000418188800003 ()2-s2.0-85049321134 (Scopus ID)
Funder
Swedish Research Council, 638-2013-9243Knut and Alice Wallenberg Foundation, KAW 2014.0048
Note

QC 20181217

Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2018-12-17Bibliographically approved
Mitra, D. & Perlekar, P. (2018). Topology of two-dimensional turbulent flows of dust and gas. Physical Review Fluids, 3(4), Article ID 044303.
Open this publication in new window or tab >>Topology of two-dimensional turbulent flows of dust and gas
2018 (English)In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 3, no 4, article id 044303Article in journal (Refereed) Published
Abstract [en]

We perform direct numerical simulations (DNS) of passive heavy inertial particles (dust) in homogeneous and isotropic two-dimensional turbulent flows (gas) for a range of Stokes number, St < 1. We solve for the particles using both a Lagrangian and an Eulerian approach (with a shock-capturing scheme). In the latter, the particles are described by a dust-density field and a dust-velocity field. We find the following: the dust-density field in our Eulerian simulations has the same correlation dimension d(2) as obtained from the clustering of particles in the Lagrangian simulations for St < 1; the cumulative probability distribution function of the dust density coarse grained over a scale r, in the inertial range, has a left tail with a power-law falloff indicating the presence of voids; the energy spectrum of the dust velocity has a power-law range with an exponent that is the same as the gas-velocity spectrum except at very high Fourier modes; the compressibility of the dust-velocity field is proportional to St(2). We quantify the topological properties of the dust velocity and the gas velocity through their gradient matrices, called A and B, respectively. Our DNS confirms that the statistics of topological properties of B are the same in Eulerian and Lagrangian frames only if the Eulerian data are weighed by the dust density. We use this correspondence to study the statistics of topological properties of A in the Lagrangian frame from our Eulerian simulations by calculating density-weighted probability distribution functions. We further find that in the Lagrangian frame, the mean value of the trace of A is negative and its magnitude increases with St approximately as exp(-C/St) with a constant C approximate to 0.1. The statistical distribution of different topological structures that appear in the dust flow is different in Eulerian and Lagrangian (density-weighted Eulerian) cases, particularly for St close to unity. In both of these cases, for small St the topological structures have close to zero divergence and are either vortical (elliptic) or strain dominated (hyperbolic, saddle). As St increases, the contribution to negative divergence comes mostly from saddles and the contribution to positive divergence comes from both vortices and saddles. Compared to the Eulerian case, the Lagrangian (density-weighted Eulerian) case has less outward spirals and more converging saddles. Inward spirals are the least probable topological structures in both cases.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-226761 (URN)10.1103/PhysRevFluids.3.044303 (DOI)000429779500001 ()2-s2.0-85047107706 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, KAW 2014.0048
Note

QC 20180503

Available from: 2018-05-03 Created: 2018-05-03 Last updated: 2019-04-04Bibliographically approved
Mitra, D., Haugen, N. E. & Rogachevskii, I. (2018). Turbophoresis in forced inhomogeneous turbulence. The European Physical Journal Plus, 133(2), Article ID 35.
Open this publication in new window or tab >>Turbophoresis in forced inhomogeneous turbulence
2018 (English)In: The European Physical Journal Plus, ISSN 2190-5444, E-ISSN 2190-5444, Vol. 133, no 2, article id 35Article in journal (Refereed) Published
Abstract [en]

We show, by direct numerical simulations, that heavy inertial particles (characterized by Stokes number St) in inhomogeneously forced statistically stationary isothermal turbulent flows cluster at the minima of mean-square turbulent velocity. Two turbulent transport processes, turbophoresis and turbulent diffusion together determine the spatial distribution of the particles. If the turbulent diffusivity is assumed to scale with turbulent root-mean-square velocity, as is the case for homogeneous turbulence, the turbophoretic coefficient can be calculated. Indeed, for the above assumption, the non-dimensional product of the turbophoretic coefficient and the rms velocity is shown to increase with St for small St, reach a maxima for St approximate to 10 and decrease as similar to St(-0.33) for large St.

Place, publisher, year, edition, pages
SPRINGER HEIDELBERG, 2018
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-224033 (URN)10.1140/epjp/i2018-11865-7 (DOI)000425526700001 ()2-s2.0-85041742597 (Scopus ID)
Note

QC 20180320

Available from: 2018-03-20 Created: 2018-03-20 Last updated: 2018-03-20Bibliographically approved
Kruger, J., Haugen, N. E. L., Mitra, D. & Lovas, T. (2017). The effect of turbulent clustering on particle reactivity. Proceedings of the Combustion Institute, 36(2), 2333-2340
Open this publication in new window or tab >>The effect of turbulent clustering on particle reactivity
2017 (English)In: Proceedings of the Combustion Institute, ISSN 1540-7489, E-ISSN 1873-2704, Vol. 36, no 2, p. 2333-2340Article in journal (Refereed) Published
Abstract [en]

The effect of turbulence on the heterogeneous (solid-fluid) reactions of solid particles is studied numerically with Direct Numerical Simulations (DNS). A simplified reaction system is used, where the solid-fluid reaction is represented by a single isothermal reaction step. It is found that, due to the clustering of particles by the isotropic turbulence, the overall reaction rate is entirely controlled by the turbulence for large Damkohler numbers. The particle clustering significantly slows down the reaction rate for increasing Damkohler numbers which reaches an asymptotic limit that can be analytically derived. This implies that the effect of turbulence on heterogeneously reacting particles should be included in models that are used in CFD simulations of e. g. char burnout in combustors or gasifiers. Such a model, based on the chemical and turbulent time scales, is here proposed for the heterogeneous reaction rate in the presence of turbulence.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE INC, 2017
Keywords
Turbulent reacting multiphase flow, Char oxidation, Clustering
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-205166 (URN)10.1016/j.proci.2016.06.187 (DOI)000397458900078 ()2-s2.0-84996848793 (Scopus ID)
Note

QC 20170412

Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-11-29Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-6162-7112

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