---
_id: '12726'
abstract:
- lang: eng
text: "Most motions of many-body systems at any scale in nature with sufficient
degrees\r\nof freedom tend to be chaotic; reaching from the orbital motion of
planets, the air\r\ncurrents in our atmosphere, down to the water flowing through
our pipelines or\r\nthe movement of a population of bacteria. To the observer
it is therefore intriguing\r\nwhen a moving collective exhibits order. Collective
motion of flocks of birds, schools\r\nof fish or swarms of self-propelled particles
or robots have been studied extensively\r\nover the past decades but the mechanisms
involved in the transition from chaos to\r\norder remain unclear. Here, the interactions,
that in most systems give rise to chaos,\r\nsustain order. In this thesis we investigate
mechanisms that preserve, destabilize\r\nor lead to the ordered state. We show
that endothelial cells migrating in circular\r\nconfinements transition to a collective
rotating state and concomitantly synchronize\r\nthe frequencies of nucleating
actin waves within individual cells. Consequently,\r\nthe frequency dependent
cell migration speed uniformizes across the population.\r\nComplementary to the
WAVE dependent nucleation of traveling actin waves, we\r\nshow that in leukocytes
the actin polymerization depending on WASp generates\r\npushing forces locally
at stationary patches. Next, in pipe flows, we study methods\r\nto disrupt the
self–sustaining cycle of turbulence and therefore relaminarize the\r\nflow. While
we find in pulsating flow conditions that turbulence emerges through a\r\nhelical
instability during the decelerating phase. Finally, we show quantitatively in\r\nbrain
slices of mice that wild-type control neurons can compensate the migratory\r\ndeficits
of a genetically modified neuronal sub–population in the developing cortex."
acknowledged_ssus:
- _id: M-Shop
- _id: Bio
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Michael
full_name: Riedl, Michael
id: 3BE60946-F248-11E8-B48F-1D18A9856A87
last_name: Riedl
orcid: 0000-0003-4844-6311
citation:
ama: Riedl M. Synchronization in collectively moving active matter. 2023. doi:10.15479/at:ista:12726
apa: Riedl, M. (2023). Synchronization in collectively moving active matter.
Institute of Science and Technology Austria. https://doi.org/10.15479/at:ista:12726
chicago: Riedl, Michael. “Synchronization in Collectively Moving Active Matter.”
Institute of Science and Technology Austria, 2023. https://doi.org/10.15479/at:ista:12726.
ieee: M. Riedl, “Synchronization in collectively moving active matter,” Institute
of Science and Technology Austria, 2023.
ista: Riedl M. 2023. Synchronization in collectively moving active matter. Institute
of Science and Technology Austria.
mla: Riedl, Michael. Synchronization in Collectively Moving Active Matter.
Institute of Science and Technology Austria, 2023, doi:10.15479/at:ista:12726.
short: M. Riedl, Synchronization in Collectively Moving Active Matter, Institute
of Science and Technology Austria, 2023.
date_created: 2023-03-15T13:22:13Z
date_published: 2023-03-23T00:00:00Z
date_updated: 2023-11-30T10:55:13Z
day: '23'
ddc:
- '530'
degree_awarded: PhD
department:
- _id: GradSch
- _id: BjHo
doi: 10.15479/at:ista:12726
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date_created: 2023-03-23T12:49:23Z
date_updated: 2023-11-24T11:57:46Z
description: the main file is missing the bibliography. See new thesis record 14530
for updated files.
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status: public
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status: public
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relation: part_of_dissertation
status: public
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status: public
status: public
supervisor:
- first_name: Björn
full_name: Hof, Björn
id: 3A374330-F248-11E8-B48F-1D18A9856A87
last_name: Hof
orcid: 0000-0003-2057-2754
title: Synchronization in collectively moving active matter
type: dissertation
user_id: 8b945eb4-e2f2-11eb-945a-df72226e66a9
year: '2023'
...
---
_id: '14530'
abstract:
- lang: eng
text: 'Most motions of many-body systems at any scale in nature with sufficient
degrees of freedom tend to be chaotic; reaching from the orbital motion of planets,
the air currents in our atmosphere, down to the water flowing through our pipelines
or the movement of a population of bacteria. To the observer it is therefore intriguing
when a moving collective exhibits order. Collective motion of flocks of birds,
schools of fish or swarms of self-propelled particles or robots have been studied
extensively over the past decades but the mechanisms involved in the transition
from chaos to order remain unclear. Here, the interactions, that in most systems
give rise to chaos, sustain order. In this thesis we investigate mechanisms that
preserve, destabilize or lead to the ordered state. We show that endothelial cells
migrating in circular confinements transition to a collective rotating state and
concomitantly synchronize the frequencies of nucleating actin waves within individual
cells. Consequently, the frequency dependent cell migration speed uniformizes
across the population. Complementary to the WAVE dependent nucleation of traveling
actin waves, we show that in leukocytes the actin polymerization depending on
WASp generates pushing forces locally at stationary patches. Next, in pipe flows,
we study methods to disrupt the self--sustaining cycle of turbulence and therefore
relaminarize the flow. While we find in pulsating flow conditions that turbulence
emerges through a helical instability during the decelerating phase. Finally,
we show quantitatively in brain slices of mice that wild-type control neurons
can compensate the migratory deficits of a genetically modified neuronal sub--population
in the developing cortex. '
acknowledged_ssus:
- _id: M-Shop
- _id: Bio
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Michael
full_name: Riedl, Michael
id: 3BE60946-F248-11E8-B48F-1D18A9856A87
last_name: Riedl
orcid: 0000-0003-4844-6311
citation:
ama: Riedl M. Synchronization in collectively moving active matter. 2023. doi:10.15479/14530
apa: Riedl, M. (2023). Synchronization in collectively moving active matter.
Institute of Science and Technology Austria. https://doi.org/10.15479/14530
chicago: Riedl, Michael. “Synchronization in Collectively Moving Active Matter.”
Institute of Science and Technology Austria, 2023. https://doi.org/10.15479/14530.
ieee: M. Riedl, “Synchronization in collectively moving active matter,” Institute
of Science and Technology Austria, 2023.
ista: Riedl M. 2023. Synchronization in collectively moving active matter. Institute
of Science and Technology Austria.
mla: Riedl, Michael. Synchronization in Collectively Moving Active Matter.
Institute of Science and Technology Austria, 2023, doi:10.15479/14530.
short: M. Riedl, Synchronization in Collectively Moving Active Matter, Institute
of Science and Technology Austria, 2023.
date_created: 2023-11-15T09:59:03Z
date_published: 2023-11-16T00:00:00Z
date_updated: 2023-11-30T10:55:13Z
day: '16'
ddc:
- '530'
- '570'
degree_awarded: PhD
department:
- _id: GradSch
- _id: MiSi
doi: 10.15479/14530
file:
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checksum: 52e1d0ab6c1abe59c82dfe8c9ff5f83a
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date_updated: 2023-11-15T09:52:54Z
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file_size: 36743942
relation: main_file
success: 1
file_date_updated: 2023-11-15T09:52:54Z
has_accepted_license: '1'
keyword:
- Synchronization
- Collective Movement
- Active Matter
- Cell Migration
- Active Colloids
language:
- iso: eng
month: '11'
oa: 1
oa_version: Updated Version
page: '260'
publication_identifier:
issn:
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publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
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status: public
- id: '461'
relation: part_of_dissertation
status: public
- id: '12726'
relation: old_edition
status: public
status: public
supervisor:
- first_name: Björn
full_name: Hof, Björn
id: 3A374330-F248-11E8-B48F-1D18A9856A87
last_name: Hof
orcid: 0000-0003-2057-2754
title: Synchronization in collectively moving active matter
type: dissertation
user_id: 8b945eb4-e2f2-11eb-945a-df72226e66a9
year: '2023'
...
---
_id: '14641'
acknowledged_ssus:
- _id: LifeSc
- _id: Bio
- _id: CampIT
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Mike
full_name: Hennessey-Wesen, Mike
id: 3F338C72-F248-11E8-B48F-1D18A9856A87
last_name: Hennessey-Wesen
citation:
ama: Hennessey-Wesen M. Adaptive mutation in E. coli modulated by luxS. 2023. doi:10.15479/at:ista:14641
apa: Hennessey-Wesen, M. (2023). Adaptive mutation in E. coli modulated by luxS.
Institute of Science and Technology Austria. https://doi.org/10.15479/at:ista:14641
chicago: Hennessey-Wesen, Mike. “Adaptive Mutation in E. Coli Modulated by LuxS.”
Institute of Science and Technology Austria, 2023. https://doi.org/10.15479/at:ista:14641.
ieee: M. Hennessey-Wesen, “Adaptive mutation in E. coli modulated by luxS,” Institute
of Science and Technology Austria, 2023.
ista: Hennessey-Wesen M. 2023. Adaptive mutation in E. coli modulated by luxS. Institute
of Science and Technology Austria.
mla: Hennessey-Wesen, Mike. Adaptive Mutation in E. Coli Modulated by LuxS.
Institute of Science and Technology Austria, 2023, doi:10.15479/at:ista:14641.
short: M. Hennessey-Wesen, Adaptive Mutation in E. Coli Modulated by LuxS, Institute
of Science and Technology Austria, 2023.
date_created: 2023-12-04T13:17:37Z
date_published: 2023-11-30T00:00:00Z
date_updated: 2023-12-07T14:12:25Z
day: '30'
ddc:
- '570'
degree_awarded: PhD
department:
- _id: GradSch
- _id: BjHo
doi: 10.15479/at:ista:14641
ec_funded: 1
file:
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checksum: 4127c285b34f4bf7fb31ef24f9d14c25
content_type: application/vnd.oasis.opendocument.text
creator: mhenness
date_created: 2023-12-06T13:13:26Z
date_updated: 2023-12-06T13:13:26Z
file_id: '14648'
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file_size: 46405919
relation: source_file
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checksum: f5203a61eddaf35235bbc51904d73982
content_type: application/pdf
creator: mhenness
date_created: 2023-12-06T13:14:15Z
date_updated: 2023-12-06T13:14:15Z
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file_id: '14649'
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file_size: 21282155
relation: main_file
file_date_updated: 2023-12-06T13:14:15Z
has_accepted_license: '1'
keyword:
- microfluidics
- miceobiology
- mutations
- quorum sensing
language:
- iso: eng
month: '11'
oa_version: Published Version
page: '104'
project:
- _id: 2564DBCA-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '665385'
name: International IST Doctoral Program
publication_identifier:
issn:
- 2663 - 337X
publication_status: published
publisher: Institute of Science and Technology Austria
status: public
supervisor:
- first_name: Björn
full_name: Hof, Björn
id: 3A374330-F248-11E8-B48F-1D18A9856A87
last_name: Hof
orcid: 0000-0003-2057-2754
title: Adaptive mutation in E. coli modulated by luxS
type: dissertation
user_id: 8b945eb4-e2f2-11eb-945a-df72226e66a9
year: '2023'
...
---
_id: '9728'
abstract:
- lang: eng
text: "Most real-world flows are multiphase, yet we know little about them compared
to their single-phase counterparts. Multiphase flows are more difficult to investigate
as their dynamics occur in large parameter space and involve complex phenomena
such as preferential concentration, turbulence modulation, non-Newtonian rheology,
etc. Over the last few decades, experiments in particle-laden flows have taken
a back seat in favour of ever-improving computational resources. However, computers
are still not powerful enough to simulate a real-world fluid with millions of
finite-size particles. Experiments are essential not only because they offer a
reliable way to investigate real-world multiphase flows but also because they
serve to validate numerical studies and steer the research in a relevant direction.
In this work, we have experimentally investigated particle-laden flows in pipes,
and in particular, examined the effect of particles on the laminar-turbulent transition
and the drag scaling in turbulent flows.\r\n\r\nFor particle-laden pipe flows,
an earlier study [Matas et al., 2003] reported how the sub-critical (i.e., hysteretic)
transition that occurs via localised turbulent structures called puffs is affected
by the addition of particles. In this study, in addition to this known transition,
we found a super-critical transition to a globally fluctuating state with increasing
particle concentration. At the same time, the Newtonian-type transition via puffs
is delayed to larger Reynolds numbers. At an even higher concentration, only the
globally fluctuating state is found. The dynamics of particle-laden flows are
hence determined by two competing instabilities that give rise to three flow regimes:
Newtonian-type turbulence at low, a particle-induced globally fluctuating state
at high, and a coexistence state at intermediate concentrations.\r\n\r\nThe effect
of particles on turbulent drag is ambiguous, with studies reporting drag reduction,
no net change, and even drag increase. The ambiguity arises because, in addition
to particle concentration, particle shape, size, and density also affect the net
drag. Even similar particles might affect the flow dissimilarly in different Reynolds
number and concentration ranges. In the present study, we explored a wide range
of both Reynolds number and concentration, using spherical as well as cylindrical
particles. We found that the spherical particles do not reduce drag while the
cylindrical particles are drag-reducing within a specific Reynolds number interval.
The interval strongly depends on the particle concentration and the relative size
of the pipe and particles. Within this interval, the magnitude of drag reduction
reaches a maximum. These drag reduction maxima appear to fall onto a distinct
power-law curve irrespective of the pipe diameter and particle concentration,
and this curve can be considered as the maximum drag reduction asymptote for a
given fibre shape. Such an asymptote is well known for polymeric flows but had
not been identified for particle-laden flows prior to this work."
acknowledged_ssus:
- _id: M-Shop
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Nishchal
full_name: Agrawal, Nishchal
id: 469E6004-F248-11E8-B48F-1D18A9856A87
last_name: Agrawal
citation:
ama: Agrawal N. Transition to turbulence and drag reduction in particle-laden pipe
flows. 2021. doi:10.15479/at:ista:9728
apa: Agrawal, N. (2021). Transition to turbulence and drag reduction in particle-laden
pipe flows. Institute of Science and Technology Austria. https://doi.org/10.15479/at:ista:9728
chicago: Agrawal, Nishchal. “Transition to Turbulence and Drag Reduction in Particle-Laden
Pipe Flows.” Institute of Science and Technology Austria, 2021. https://doi.org/10.15479/at:ista:9728.
ieee: N. Agrawal, “Transition to turbulence and drag reduction in particle-laden
pipe flows,” Institute of Science and Technology Austria, 2021.
ista: Agrawal N. 2021. Transition to turbulence and drag reduction in particle-laden
pipe flows. Institute of Science and Technology Austria.
mla: Agrawal, Nishchal. Transition to Turbulence and Drag Reduction in Particle-Laden
Pipe Flows. Institute of Science and Technology Austria, 2021, doi:10.15479/at:ista:9728.
short: N. Agrawal, Transition to Turbulence and Drag Reduction in Particle-Laden
Pipe Flows, Institute of Science and Technology Austria, 2021.
date_created: 2021-07-27T13:40:30Z
date_published: 2021-07-29T00:00:00Z
date_updated: 2024-02-28T13:14:39Z
day: '29'
ddc:
- '532'
degree_awarded: PhD
department:
- _id: GradSch
- _id: BjHo
doi: 10.15479/at:ista:9728
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file_date_updated: 2022-07-29T22:30:05Z
has_accepted_license: '1'
keyword:
- Drag Reduction
- Transition to Turbulence
- Multiphase Flows
- particle Laden Flows
- Complex Flows
- Experiments
- Fluid Dynamics
language:
- iso: eng
license: https://creativecommons.org/licenses/by/4.0/
month: '07'
oa: 1
oa_version: Published Version
page: '118'
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
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relation: part_of_dissertation
status: public
status: public
supervisor:
- first_name: Björn
full_name: Hof, Björn
id: 3A374330-F248-11E8-B48F-1D18A9856A87
last_name: Hof
orcid: 0000-0003-2057-2754
title: Transition to turbulence and drag reduction in particle-laden pipe flows
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: dissertation
user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1
year: '2021'
...
---
_id: '8350'
abstract:
- lang: eng
text: "Cytoplasm is a gel-like crowded environment composed of tens of thousands
of macromolecules, organelles, cytoskeletal networks and cytosol. The structure
of the cytoplasm is thought to be highly organized and heterogeneous due to the
crowding of its constituents and their effective compartmentalization. In such
an environment, the diffusive dynamics of the molecules is very restricted, an
effect that is further amplified by clustering and anchoring of molecules. Despite
the jammed nature of the cytoplasm at the microscopic scale, large-scale reorganization
of cytoplasm is essential for important cellular functions, such as nuclear positioning
and cell division. How such mesoscale reorganization of the cytoplasm is achieved,
especially for very large cells such as oocytes or syncytial tissues that can
span hundreds of micrometers in size, has only begun to be understood.\r\nIn this
thesis, I focus on the recent advances in elucidating the molecular, cellular
and biophysical principles underlying cytoplasmic organization across different
scales, structures and species. First, I outline which of these principles have
been identified by reductionist approaches, such as in vitro reconstitution assays,
where boundary conditions and components can be modulated at ease. I then describe
how the theoretical and experimental framework established in these reduced systems
have been applied to their more complex in vivo counterparts, in particular oocytes
and embryonic syncytial structures, and discuss how such complex biological systems
can initiate symmetry breaking and establish patterning.\r\nSpecifically, I examine
an example of large-scale reorganizations taking place in zebrafish embryos, where
extensive cytoplasmic streaming leads to the segregation of cytoplasm from yolk
granules along the animal-vegetal axis of the embryo. Using biophysical experimentation
and theory, I investigate the forces underlying this process, to show that this
process does not rely on cortical actin reorganization, as previously thought,
but instead on a cell-cycle-dependent bulk actin polymerization wave traveling
from the animal to the vegetal pole of the embryo. This wave functions in segregation
by both pulling cytoplasm animally and pushing yolk granules vegetally. Cytoplasm
pulling is mediated by bulk actin network flows exerting friction forces on the
cytoplasm, while yolk granule pushing is achieved by a mechanism closely resembling
actin comet formation on yolk granules. This study defines a novel role of bulk
actin polymerization waves in embryo polarization via cytoplasmic segregation.
Lastly, I describe the cytoplasmic reorganizations taking place during zebrafish
oocyte maturation, where the initial segregation of the cytoplasm and yolk granules
occurs. Here, I demonstrate a previously uncharacterized wave of microtubule aster
formation, traveling the oocyte along the animal-vegetal axis. Further research
is required to determine the role of such microtubule structures in cytoplasmic
reorganizations therein.\r\nCollectively, these studies provide further evidence
for the coupling between cell cytoskeleton and cell cycle machinery, which can
underlie a core self-organizing mechanism for orchestrating large-scale reorganizations
in a cell-cycle-tunable manner, where the modulations of the force-generating
machinery and cytoplasmic mechanics can be harbored to fulfill cellular functions."
acknowledged_ssus:
- _id: PreCl
- _id: Bio
- _id: EM-Fac
acknowledgement: "I would have had no fish and hence no results without our wonderful
fish facility crew, Verena Mayer, Eva Schlegl, Andreas Mlak and Matthias Nowak.
Special thanks to Verena for being always happy to help and dealing with our chaotic
schedules in the lab. Danke auch, Verena, für deine Geduld, mit mir auf Deutsch
zu sprechen. Das hat mir sehr geholfen.\r\nSpecial thanks to the Bioimaging and
EM facilities at IST Austria for supporting us every day. Very special thanks would
go to Robert Hauschild for his continuous support on data analysis and also to Jack
Merrin for designing and building microfabricated chambers for the project and for
the various discussions on making zebrafish extracts."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Shayan
full_name: Shamipour, Shayan
id: 40B34FE2-F248-11E8-B48F-1D18A9856A87
last_name: Shamipour
citation:
ama: Shamipour S. Bulk actin dynamics drive phase segregation in zebrafish oocytes
. 2020. doi:10.15479/AT:ISTA:8350
apa: Shamipour, S. (2020). Bulk actin dynamics drive phase segregation in zebrafish
oocytes . Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:8350
chicago: Shamipour, Shayan. “Bulk Actin Dynamics Drive Phase Segregation in Zebrafish
Oocytes .” Institute of Science and Technology Austria, 2020. https://doi.org/10.15479/AT:ISTA:8350.
ieee: S. Shamipour, “Bulk actin dynamics drive phase segregation in zebrafish oocytes
,” Institute of Science and Technology Austria, 2020.
ista: Shamipour S. 2020. Bulk actin dynamics drive phase segregation in zebrafish
oocytes . Institute of Science and Technology Austria.
mla: Shamipour, Shayan. Bulk Actin Dynamics Drive Phase Segregation in Zebrafish
Oocytes . Institute of Science and Technology Austria, 2020, doi:10.15479/AT:ISTA:8350.
short: S. Shamipour, Bulk Actin Dynamics Drive Phase Segregation in Zebrafish Oocytes
, Institute of Science and Technology Austria, 2020.
date_created: 2020-09-09T11:12:10Z
date_published: 2020-09-09T00:00:00Z
date_updated: 2023-09-27T14:16:45Z
day: '09'
ddc:
- '570'
degree_awarded: PhD
department:
- _id: BjHo
- _id: CaHe
doi: 10.15479/AT:ISTA:8350
file:
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checksum: 6e47871c74f85008b9876112eb3fcfa1
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date_created: 2020-09-09T11:06:27Z
date_updated: 2021-09-11T22:30:05Z
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file_size: 65194814
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creator: sshamip
date_created: 2020-09-09T11:06:13Z
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file_date_updated: 2021-09-11T22:30:05Z
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language:
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month: '09'
oa: 1
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page: '107'
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
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status: public
- id: '735'
relation: part_of_dissertation
status: public
status: public
supervisor:
- first_name: Carl-Philipp J
full_name: Heisenberg, Carl-Philipp J
id: 39427864-F248-11E8-B48F-1D18A9856A87
last_name: Heisenberg
orcid: 0000-0002-0912-4566
- first_name: Björn
full_name: Hof, Björn
id: 3A374330-F248-11E8-B48F-1D18A9856A87
last_name: Hof
orcid: 0000-0003-2057-2754
title: 'Bulk actin dynamics drive phase segregation in zebrafish oocytes '
type: dissertation
user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1
year: '2020'
...
---
_id: '7258'
abstract:
- lang: eng
text: Many flows encountered in nature and applications are characterized by a chaotic
motion known as turbulence. Turbulent flows generate intense friction with pipe
walls and are responsible for considerable amounts of energy losses at world scale.
The nature of turbulent friction and techniques aimed at reducing it have been
subject of extensive research over the last century, but no definite answer has
been found yet. In this thesis we show that in pipes at moderate turbulent Reynolds
numbers friction is better described by the power law first introduced by Blasius
and not by the Prandtl–von Kármán formula. At higher Reynolds numbers, large scale
motions gradually become more important in the flow and can be related to the
change in scaling of friction. Next, we present a series of new techniques that
can relaminarize turbulence by suppressing a key mechanism that regenerates it
at walls, the lift–up effect. In addition, we investigate the process of turbulence
decay in several experiments and discuss the drag reduction potential. Finally,
we examine the behavior of friction under pulsating conditions inspired by the
human heart cycle and we show that under such circumstances turbulent friction
can be reduced to produce energy savings.
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Davide
full_name: Scarselli, Davide
id: 40315C30-F248-11E8-B48F-1D18A9856A87
last_name: Scarselli
orcid: 0000-0001-5227-4271
citation:
ama: Scarselli D. New approaches to reduce friction in turbulent pipe flow. 2020.
doi:10.15479/AT:ISTA:7258
apa: Scarselli, D. (2020). New approaches to reduce friction in turbulent pipe
flow. Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:7258
chicago: Scarselli, Davide. “New Approaches to Reduce Friction in Turbulent Pipe
Flow.” Institute of Science and Technology Austria, 2020. https://doi.org/10.15479/AT:ISTA:7258.
ieee: D. Scarselli, “New approaches to reduce friction in turbulent pipe flow,”
Institute of Science and Technology Austria, 2020.
ista: Scarselli D. 2020. New approaches to reduce friction in turbulent pipe flow.
Institute of Science and Technology Austria.
mla: Scarselli, Davide. New Approaches to Reduce Friction in Turbulent Pipe Flow.
Institute of Science and Technology Austria, 2020, doi:10.15479/AT:ISTA:7258.
short: D. Scarselli, New Approaches to Reduce Friction in Turbulent Pipe Flow, Institute
of Science and Technology Austria, 2020.
date_created: 2020-01-12T16:07:26Z
date_published: 2020-01-13T00:00:00Z
date_updated: 2023-09-15T12:20:08Z
day: '13'
ddc:
- '532'
degree_awarded: PhD
department:
- _id: BjHo
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language:
- iso: eng
month: '01'
oa: 1
oa_version: None
page: '174'
project:
- _id: 25152F3A-B435-11E9-9278-68D0E5697425
call_identifier: FP7
grant_number: '306589'
name: Decoding the complexity of turbulence at its origin
- _id: 25104D44-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '737549'
name: Eliminating turbulence in oil pipelines
- _id: 25136C54-B435-11E9-9278-68D0E5697425
grant_number: HO 4393/1-2
name: Experimental studies of the turbulence transition and transport processes
in turbulent Taylor-Couette currents
publication_identifier:
issn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
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relation: part_of_dissertation
status: public
- id: '6486'
relation: part_of_dissertation
status: public
- id: '461'
relation: part_of_dissertation
status: public
- id: '422'
relation: part_of_dissertation
status: public
status: public
supervisor:
- first_name: Björn
full_name: Hof, Björn
id: 3A374330-F248-11E8-B48F-1D18A9856A87
last_name: Hof
orcid: 0000-0003-2057-2754
title: New approaches to reduce friction in turbulent pipe flow
type: dissertation
user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1
year: '2020'
...
---
_id: '6957'
abstract:
- lang: eng
text: "In many shear flows like pipe flow, plane Couette flow, plane Poiseuille
flow, etc. turbulence emerges subcritically. Here, when subjected to strong enough
perturbations, the flow becomes turbulent in spite of the laminar base flow being
linearly stable. The nature of this instability has puzzled the scientific community
for decades. At onset, turbulence appears in localized patches and flows are spatio-temporally
intermittent. In pipe flow the localized turbulent structures are referred to
as puffs and in planar flows like plane Couette and channel flow, patches arise
in the form of localized oblique bands. In this thesis, we study the onset of
turbulence in channel flow in direct numerical simulations from a dynamical system
theory perspective, as well as by performing experiments in a large aspect ratio
channel.\r\n\r\nThe aim of the experimental work is to determine the critical
Reynolds number where turbulence first becomes sustained. Recently, the onset
of turbulence has been described in analogy to absorbing state phase transition
(i.e. directed percolation). In particular, it has been shown that the critical
point can be estimated from the competition between spreading and decay processes.
Here, by performing experiments, we identify the mechanisms underlying turbulence
proliferation in channel flow and find the critical Reynolds number, above which
turbulence becomes sustained. Above the critical point, the continuous growth
at the tip of the stripes outweighs the stochastic shedding of turbulent patches
at the tail and the stripes expand. For growing stripes, the probability to decay
decreases while the probability of stripe splitting increases. Consequently, and
unlike for the puffs in pipe flow, neither of these two processes is time-independent
i.e. memoryless. Coupling between stripe expansion and creation of new stripes
via splitting leads to a significantly lower critical point ($Re_c=670+/-10$)
than most earlier studies suggest. \r\n\r\nWhile the above approach sheds light
on how turbulence first becomes sustained, it provides no insight into the origin
of the stripes themselves. In the numerical part of the thesis we investigate
how turbulent stripes form from invariant solutions of the Navier-Stokes equations.
The origin of these turbulent stripes can be identified by applying concepts from
the dynamical system theory. In doing so, we identify the exact coherent structures
underlying stripes and their bifurcations and how they give rise to the turbulent
attractor in phase space. We first report a family of localized nonlinear traveling
wave solutions of the Navier-Stokes equations in channel flow. These solutions
show structural similarities with turbulent stripes in experiments like obliqueness,
quasi-streamwise streaks and vortices, etc. A parametric study of these traveling
wave solution is performed, with parameters like Reynolds number, stripe tilt
angle and domain size, including the stability of the solutions. These solutions
emerge through saddle-node bifurcations and form a phase space skeleton for the
turbulent stripes observed in the experiments. The lower branches of these TW
solutions at different tilt angles undergo Hopf bifurcation and new solutions
branches of relative periodic orbits emerge. These RPO solutions do not belong
to the same family and therefore the routes to chaos for different angles are
different. \r\n\r\nIn shear flows, turbulence at onset is transient in nature.
\ Consequently,turbulence can not be tracked to lower Reynolds numbers, where
the dynamics may simplify. Before this happens, turbulence becomes short-lived
and laminarizes. In the last part of the thesis, we show that using numerical
simulations we can continue turbulent stripes in channel flow past the 'relaminarization
barrier' all the way to their origin. Here, turbulent stripe dynamics simplifies
and the fluctuations are no longer stochastic and the stripe settles down to a
relative periodic orbit. This relative periodic orbit originates from the aforementioned
traveling wave solutions. Starting from the relative periodic orbit, a small increase
in speed i.e. Reynolds number gives rise to chaos and the attractor dimension
sharply increases in contrast to the classical transition scenario where the instabilities
affect the flow globally and give rise to much more gradual route to turbulence."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Chaitanya S
full_name: Paranjape, Chaitanya S
id: 3D85B7C4-F248-11E8-B48F-1D18A9856A87
last_name: Paranjape
citation:
ama: Paranjape CS. Onset of turbulence in plane Poiseuille flow. 2019. doi:10.15479/AT:ISTA:6957
apa: Paranjape, C. S. (2019). Onset of turbulence in plane Poiseuille flow.
Institute of Science and Technology Austria. https://doi.org/10.15479/AT:ISTA:6957
chicago: Paranjape, Chaitanya S. “Onset of Turbulence in Plane Poiseuille Flow.”
Institute of Science and Technology Austria, 2019. https://doi.org/10.15479/AT:ISTA:6957.
ieee: C. S. Paranjape, “Onset of turbulence in plane Poiseuille flow,” Institute
of Science and Technology Austria, 2019.
ista: Paranjape CS. 2019. Onset of turbulence in plane Poiseuille flow. Institute
of Science and Technology Austria.
mla: Paranjape, Chaitanya S. Onset of Turbulence in Plane Poiseuille Flow.
Institute of Science and Technology Austria, 2019, doi:10.15479/AT:ISTA:6957.
short: C.S. Paranjape, Onset of Turbulence in Plane Poiseuille Flow, Institute of
Science and Technology Austria, 2019.
date_created: 2019-10-22T12:08:43Z
date_published: 2019-10-24T00:00:00Z
date_updated: 2023-09-07T12:53:25Z
day: '24'
ddc:
- '532'
degree_awarded: PhD
department:
- _id: BjHo
doi: 10.15479/AT:ISTA:6957
file:
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has_accepted_license: '1'
keyword:
- Instabilities
- Turbulence
- Nonlinear dynamics
language:
- iso: eng
month: '10'
oa: 1
oa_version: Published Version
page: '138'
publication_identifier:
eissn:
- 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
status: public
supervisor:
- first_name: Björn
full_name: Hof, Björn
id: 3A374330-F248-11E8-B48F-1D18A9856A87
last_name: Hof
orcid: 0000-0003-2057-2754
title: Onset of turbulence in plane Poiseuille flow
type: dissertation
user_id: c635000d-4b10-11ee-a964-aac5a93f6ac1
year: '2019'
...