Download Project 1: Computational Modeling of Flow and Surfactant Transport

Metin Muradoglu
06.05.2017
Dear prospective graduate students,
I have four projects available in my research group. The projects are mainly supported by
TUBITAK, TUBA through the young investigator award (GEBIP) and Koc University. All
projects involve some sort of international collaborations as mentioned at the end of each
project.
Short descriptions of the available projects are provided below. For details of the project and
research opportunities, please directly contact me via e-mail or phone.
Project 1: Computational Modeling of Flow and Surfactant Transport in an Alveolus
Partially Filled with Liquid
Short Abstract: The flow and transport in an alveolus are of fundamental importance in
partial liquid ventilation, pulmonary drug administration, cell-cell signaling pathways, gene
therapy and surfactant transport in alveolus. Alveolus are the major units responsible for gas
(O2-CO2) exchange in the lung. Surfactant is normally produced by the lung to reduce the
surface tension in the alveolus in order to make the lung more compliant to aid in breathing.
Lack of surfactant production results in Respiratory Distress Syndrome (RDS) especially in
premature newborn babies. In addition, Acute Distress Syndrome (ARDS) may results in total
collapse of alveoli. These diseases are often remedied by surfactant replacement therapy
(SRT) or by partial liquid ventilation (PLV). In both cases, it is crucial to understand the flow
and surfactant transport in the system. In this project, a front-tracking/finite-difference
method will be developed for direct simulation of flow and mass transfer in an alveolus that is
partially filled with liquid containing soluble surfactants.
(a)
(b)
(c)
Figure 1: Surfactant produced by lung reduces the surface tension making the lung more
compliant to aid in breathing. Lack of surfactant results in Respiratory Distress
Syndrome(RDS) especially in premature newborn babies [Avery vd. 2006]. (a) Pulmonary
system. (b) Type A and type B alveolus. (c) Proposed front-tracking/finite-difference model.
Sponsors: TUBITAK and TUBA-GEBIP
Collaborators: Prof. A. Szeri and Savaş Taşoğlu, Department of Mechanical Engineering,
University of California, Berkeley, USA.
Requirements: A PhD student is preferred for this project but a highly motivated MS student
is also welcome. Strong background in fluid mechanics and math is required and some
knowledge in Physiology is a plus.
Metin Muradoglu
06.05.2017
Project 2: Effects of Soluble Surfactants on the Landau-Levich Problem
Short Abstract: The classical fluid mechanics problem involved in dip-coating is known to
be Landau-Levich problem. The coating is ubiquitous in many engineering and technological
applications. Therefore it has been studied extensively in the literature since the pioneering
work of Landau and Levich. Four common examples of this problem widely encountered in
applications are shown in the figure below. In the limit of vanishingly small capillary number
defined as viscous forces divided by surface tension forces, it is well known that a lubrication
theory is valid and liquid film thickness ( h ) is given by h  l c Ca 2 / 3 where l c is the length
U
scale of the flow and Ca 
is the capillary number. In spite of a vast number of studies in

this classical fluid mechanics problem, the effects of surfactants on the dip-coating are not
clear. All the theoretical and experimental studies showed that the liquid film thickness
increases with the addition of surfactant. However, direct numerical simulation performed by
Krechentnikov and Homsy demonstrated just the opposite: The surfactant reduces the fim
thickness. In this project, we’ll attempt to resolve this unexpected results using newly
developed front-tracking/finite-difference method developed by Muradoglu and Tryggvason
(2008).
U
Vapor
h
Plate
coating
Landau-
h
Liquid
Levich
Vapor

r,
m
Liquid
n
h
Liquid
U
Fiber coating
Roll coating: partially immersed
roller Wilkinso
h
Vapor
U
Liquid
Derjagui
n
Vapor
2
b
Bubbles moving in a capillary
Coating inside a tube or Hele-Shaw cell
Liquid
Bretherto
n
Figure 2: Examples of dip-coating (Landau-Levich) problem. It turns out that all of these
problems are the same.
Sponsors: TUBITAK and TUBA-GEBIP
Requirements: Strong background in fluid mechanics and mathematics. Experience in
asymptotic methods and numerical techniques are a plus.
Metin Muradoglu
06.05.2017
Project 3: LES/FDF modeling of turbulent combustion
Short Abstract: This project intends to take the advantages of large eddy simulation (LES) to
treat turbulent flow and the probability density function (PDF) method to treat turbulencechemistry interactions. According to Kolmogorov’s hypothesis for turbulence, the small scale
motion of turbulent flows is universal and thus it can be modeled. The LES approach takes
advantage of these hypotheses and attempt to directly simulate large scale motion while
modeling the small scale eddies. The LES method has been successfully used for many years
in computing complex turbulent flows and proved to be the best approach in terms of
accuracy and computational time. However, it faces with the same closure problems as the
Reynolds averaged Navier-Stokes (RANS) models when the flow involves finite-rate
chemical reactions as the case in almost all industrial combustion processes including internal
combustion engines, gas turbines and chemical reactors. The reason is that the chemical
reaction takes place in small scales which are modeled in LES. On the other has, PDF model
can treat chemical reactions exactly without any modeling assumptions. Therefore the
combination of LES and PDF methods through filtered density function (FDF) is the ideal for
reacting turbulent flows. In comparison to Reynolds averaged simulations, the LES/FDF
methodology provides a more detailed description of turbulent reacting flows and is able to
predict the compositional structure of the flame, which is of crucial importance especially in
predicting the local extinction and reignition processes that are key processes responsible for
emission.
In this project, LES/FDF method will be combined with the in situ adaptive tabulation (ISAT)
methodology and will be used to simulate reacting turbulent flames of practical interest.
Sponsors: TUBA-GEBIP. In addition, proposals will be submitted to European Union FP7
and TUBITAK on this subject.
Collaborators: Prof. Y. Kim of Hanyang University, Seoul, S. Korea and Prof. S.B. Pope of
Cornell University, Ithaca, NY, USA.
Requirements: A PhD student is preferred for this project but a highly motivated MS student
is also welcome. Strong background in fluid mechanics and math is required and some
knowledge in turbulence and combustion is a plus.
Metin Muradoglu
06.05.2017
Project 4: Droplet deformation and manipulation using electric field
Short Abstract: This project is part of a optofluidics project to be done though a European
network within FP7 comprising research groups in England, France, Switzerland and Koç
University. In this project, we will explore mechanisms of deforming droplets using an
external electric field. It is well known that an electric field can induce both normal and
tangential forces on a fluid interface and thus induces deformation of droplet into a prolate or
oblate shape depending on the ratio of the conductivities and the dielectric properties of the
continuous and dispersed phase. The deformation of a single isolated drop suspended in a
continuous fluid has been studied extensively both analytically and computationally.
However, it is still not well understood how drop deforms when it is sitting on a hydrophobic
surface including electrowetting effect. In addition, interactions of droplet under a strong
electric filed will be also examined using direct numerical simulations of finite Reynolds
number droplet suspensions by a front tracking method. Experimental studies will also be
performed in parallel through collaboration with Prof. Alper Kiraz of Physics department.
Different micropatterned electrical contact geometries that can generate uniform or nonuniform electric fields will be explored. Full computational model of the deformation of a
droplet standing on a superhydrophobic surface under the influence of an electric field will be
developed. Interfacial electric force, the interfacial surface tension, effects due to the presence
of a superhydrophobic surface, and electrowetting will be included into the models. The
results of this task will be used in tuning liquid droplet based optofluidics devices. The results
will also have potential applications in superhydrophobic surface characterization and
biological sensing.
Figure 3: Interaction of finite Reynolds number droplets in a strong electric field. Figure is
produced by Tryggvason’s group at WPI, USA.
Sponsors: TUBA-GEBIP. European Union (pending)
Collaborators: Prof. Alper Kiraz, Department of Physics, Koc University.
Requirements: A PhD student is preferred for this project but a highly motivated MS student
is also welcome. Strong background in fluid mechanics and physics is required and some
knowledge in electrohydrodynamics and optics is a plus.