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Drop deformation and breakup
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.ORCID iD: 0000-0003-3336-1462
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0001-9976-8316
2014 (English)In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 66, 1-10 p.Article in journal (Refereed) Published
Abstract [en]

A Volume of Fluid (VOF) method is applied to investigate the deformation and breakup of an initially spherical drop in the bag- and shear breakup regimes, induced by steady disturbances. The onset of breakup is sought by studying steady-shape deformations while increasing the Weber number until breakup occurs. A parameter study is carried out applying different material properties and a wide range of drop Reynolds numbers in the steady wake regime. Density ratios of liquid to gas of 20, 40, and 80, viscosity ratios in the range 0.5-50, and Reynolds numbers between 20 and 200 are investigated for a constant Weber number of 20. The critical Weber number is found to be 12, in agreement with observations of earlier studies. For Weber number of 20 varying density, viscosity ratios and Reynolds numbers, interesting mixed breakup modes are discovered. Moreover, a new regime map including all modes observed is presented. A criterion for the transition between bag-and shear breakup is defined relating the competing inertial and shear forces appearing in the flow. Furthermore, results on breakup times and the time history of the drag coefficient are presented; the latter is concluded to be a potential parameter to indicate the occurrence of breakup. (C) 2014 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2014. Vol. 66, 1-10 p.
Keyword [en]
Droplet, Deformation, Breakup, Regime map, Breakup time, Volume of Fluid (VOF)
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-154737DOI: 10.1016/j.ijmultiphaseflow.2014.06.006ISI: 000342548300001Scopus ID: 2-s2.0-84904904082OAI: oai:DiVA.org:kth-154737DiVA: diva2:764505
Funder
Swedish Research Council
Note

QC 20141119. QC 20160113

Available from: 2014-11-19 Created: 2014-10-27 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Scenarios of drop deformation and breakup in sprays
Open this publication in new window or tab >>Scenarios of drop deformation and breakup in sprays
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sprays are used in a wide range of engineering applications, in the food and pharmaceutical industry in order to produce certain materials in the desired powder-form, or in internal combustion engines where liquid fuel is injected and atomized in order to obtain the required air/fuel mixture. The optimization of such processes requires the detailed understanding of the breakup of liquid structures.

In this work, we focus on the secondary breakup of medium size liquid drops that are the result of primary breakup at earlier stages of the breakup process, and that are subject to further breakup. The fragmentation of such drops is determined by the competing disruptive (pressure and viscous) and cohesive (surface tension) forces. In order to gain a deeper understanding on the dynamics of the deformation and breakup of such drops, numerical simulations on single drops in uniform and shear flows, and on dual drops in uniform flows are performed employing a Volume of Fluid method. The studied parameter range corresponds to an intermediate Weber number of 20, sufficiently high so that breakup occurs, but much lower than the limit for catastrophic breakup, and a range of Reynolds numbers covering the steady wake regime for liquid drops, Re = 20-200. In order to account for liquids in various applications, a set of different density and viscosity ratios are considered, ρ*=20-80, and μ*=0.5-50 respectively.

Single drop simulations show that depending on the Reynolds number and density and viscosity ratios, various breakup modes besides classical bag and shear breakup may be observed at a constant Weber number. The characteristics of the deformation process and the time required for breakup are considerably different for these modes; furthermore, both are significantly altered by velocity gradients in the flow. Dual drop simulations show that the relative position of the two drops, in addition to the Reynolds number and density and viscosity ratios, plays a crucial role in determining the interaction scenario. It is found that the behaviour of drops in tandem may be predicted based on data obtained for single drops: the breakup time and the length of the wake behind the drop. The region where collision is most likely to occur is identified as a two diameters wide and eight diameters long streak, however, weaker forms of interaction may occur up to twenty diameters behind the drop. Results presented in this thesis may be applied to formulate enhanced breakup models regarding the deformation, breakup, and interaction of liquid drops employed in spray simulations.

Place, publisher, year, edition, pages
Stockholm: Kungliga Tekniska högskolan, 2017. 60 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2017:10
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-212939 (URN)978-91-7729-500-6 (ISBN)
Public defence
2017-09-15, D3, Lindstedtsvägen 5, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20170825

Available from: 2017-08-25 Created: 2017-08-24 Last updated: 2017-11-07Bibliographically approved

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Amberg, GustavPrahl Wittberg, Lisa

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