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Interaction between two deforming liquid drops in tandem subject to uniform flow
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: timea@mech.kth.se
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

A Volume of Fluid (VOF) method is applied to study the interaction between two liquid drops in uniform flow, where the drops have the same initial diameter and are placed in tandem, for initial separation distances of l = 1.5 − 20D (drop diameters). Simulations have been performed for a We- ber number of W e = 20, Reynolds numbers in the range Re = 20 − 200, and density and viscosity ratios of ρ∗ = 20 − 80 and μ∗ = 0.5 − 50. The movement of the back drop with respect to the front drop is evaluated and presented in the form of a regime map within the adopted parameter range. Besides the initial separation distance most commonly addressed in literature in the topic, additional parameters such as the Reynolds number and density and viscosity ratios determine whether the drops collide or not. Furthermore, sequential im- ages along with the analyses of the wake around the interacting drops suggest that the time required for breakup is also crucial regarding the outcome of the interaction. Data on the length of the wake region behind a deforming drop is provided, and together with the breakup time of single drops is used to identify, and define criteria for the regimes of the various observed interaction scenarios.

Keywords [en]
drop, tandem, deformation, breakup, wake, regime map, Volume of Fluid (VOF)
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-212936OAI: oai:DiVA.org:kth-212936DiVA, id: diva2:1135957
Note

QC 20170825

Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2017-08-25Bibliographically 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. p. 60
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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