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Interacting particles and droplets at low Reynolds numbers

Prahl, Lisa LU (2007)
Abstract
The overall purpose with this work is to study the flow past particles and droplets using numerical simulations. Especially the interaction among particles and droplets have been a main objective as the results are to be used in order to improve already existing spray models. In order to represent the particulate and droplet phase, the Volume of Fluid (VOF) and the Volume of Solid (VOS) methods are used, respectively.



The variations of the drag- and lift-coefficients of two fixed solid



spherical particles placed at different positions relative each other is studied



for particle Reynolds numbers of 50, 100, 200, 300 and 600. For Reynolds numbers of 100, 300 and 600, both a uniform and... (More)
The overall purpose with this work is to study the flow past particles and droplets using numerical simulations. Especially the interaction among particles and droplets have been a main objective as the results are to be used in order to improve already existing spray models. In order to represent the particulate and droplet phase, the Volume of Fluid (VOF) and the Volume of Solid (VOS) methods are used, respectively.



The variations of the drag- and lift-coefficients of two fixed solid



spherical particles placed at different positions relative each other is studied



for particle Reynolds numbers of 50, 100, 200, 300 and 600. For Reynolds numbers of 100, 300 and 600, both a uniform and a pulsating inflow is applied to investigate the effects of flow field fluctuations. Independent of Reynolds number, particles in tandem formation are found to experience the largest effect in the drag, as compared to the single particle case. Depending on the flow situation in--between the particles for various particle arrangements, attraction and repulsion forces are detected. These forces may lead to unsteady dynamics of the particle arrangement.



The simulations of the motion of particles near a solid wall show that single and dual particles settling under gravity is clearly affected by the wall.



However, for side-by-side arrangements, the simulations show that the particle-particle interaction is stronger as compared to the wall effects. The simulations are carried out for Reynolds numbers in the range from 1 to 1000 and particle to fluid density ratios of 1.5 to 8. Both the Reynolds number and the density ratio are found



to highly influence the falling motion.



Simulations of single and dual droplets in a uniform flow for Reynolds numbers 100 and Weber numbers of 0.1 - 10 have been studied. For single droplets, Reynolds numbers of 50, 100 and 200 for the same Weber number range has also



been investigated. The results are used in order to evaluate how droplet deformation can be corrected for in



numerical models for droplets. A drag correction function is presented, showing similar trends when compared



to other drag correlations found in literature.



The results show the importance of accounting for the full interaction among droplets and particles. Such interaction has to be included even for rather dilute two-phase systems. The obtained data has already been used for correcting for the four-way interaction that is usually neglected in current models. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Docent van Wachem, Berend, Chalmers University of Technology, Göteborg
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Gases, VOS, VOF, Multiphase flow, Interaction, Particles, Droplets, fluid dynamics, plasmas, Gaser, fluiddynamik, plasma
publisher
Department of Energy Sciences, Lund University
defense location
Room M:B, M-building, Ole Römers Väg 1, Lund University Faculty of Engineering
defense date
2007-11-09 10:15
external identifiers
  • other:LUTMDN/TMHP-07/1054-SE
ISSN
0282-1990
ISBN
978-91-628-7288-5
language
English
LU publication?
yes
id
337e1875-29de-405f-b1b2-c06fc56e5585 (old id 599112)
date added to LUP
2007-11-13 08:51:40
date last changed
2016-09-19 08:44:59
@phdthesis{337e1875-29de-405f-b1b2-c06fc56e5585,
  abstract     = {The overall purpose with this work is to study the flow past particles and droplets using numerical simulations. Especially the interaction among particles and droplets have been a main objective as the results are to be used in order to improve already existing spray models. In order to represent the particulate and droplet phase, the Volume of Fluid (VOF) and the Volume of Solid (VOS) methods are used, respectively.<br/><br>
<br/><br>
The variations of the drag- and lift-coefficients of two fixed solid<br/><br>
<br/><br>
spherical particles placed at different positions relative each other is studied<br/><br>
<br/><br>
for particle Reynolds numbers of 50, 100, 200, 300 and 600. For Reynolds numbers of 100, 300 and 600, both a uniform and a pulsating inflow is applied to investigate the effects of flow field fluctuations. Independent of Reynolds number, particles in tandem formation are found to experience the largest effect in the drag, as compared to the single particle case. Depending on the flow situation in--between the particles for various particle arrangements, attraction and repulsion forces are detected. These forces may lead to unsteady dynamics of the particle arrangement.<br/><br>
<br/><br>
The simulations of the motion of particles near a solid wall show that single and dual particles settling under gravity is clearly affected by the wall.<br/><br>
<br/><br>
However, for side-by-side arrangements, the simulations show that the particle-particle interaction is stronger as compared to the wall effects. The simulations are carried out for Reynolds numbers in the range from 1 to 1000 and particle to fluid density ratios of 1.5 to 8. Both the Reynolds number and the density ratio are found<br/><br>
<br/><br>
to highly influence the falling motion.<br/><br>
<br/><br>
Simulations of single and dual droplets in a uniform flow for Reynolds numbers 100 and Weber numbers of 0.1 - 10 have been studied. For single droplets, Reynolds numbers of 50, 100 and 200 for the same Weber number range has also<br/><br>
<br/><br>
been investigated. The results are used in order to evaluate how droplet deformation can be corrected for in<br/><br>
<br/><br>
numerical models for droplets. A drag correction function is presented, showing similar trends when compared<br/><br>
<br/><br>
to other drag correlations found in literature.<br/><br>
<br/><br>
The results show the importance of accounting for the full interaction among droplets and particles. Such interaction has to be included even for rather dilute two-phase systems. The obtained data has already been used for correcting for the four-way interaction that is usually neglected in current models.},
  author       = {Prahl, Lisa},
  isbn         = {978-91-628-7288-5},
  issn         = {0282-1990},
  keyword      = {Gases,VOS,VOF,Multiphase flow,Interaction,Particles,Droplets,fluid dynamics,plasmas,Gaser,fluiddynamik,plasma},
  language     = {eng},
  publisher    = {Department of Energy Sciences, Lund University},
  school       = {Lund University},
  title        = {Interacting particles and droplets at low Reynolds numbers},
  year         = {2007},
}