---
OA_place: publisher
_id: '19684'
abstract:
- lang: eng
  text: "The overarching goal of this thesis is to break down the complexity of turbulent
    flows in terms of enumerable, coherent structures and patterns. In a five-paper
    series, we adopt a variety of perspectives and techniques to relate the properties
    of systems of increasing complexity to their underlying coherent structures. \r\n\r\nInitially,
    we take a dynamical systems point of view, seeing turbulent flow as a chaotic
    trajectory bouncing between exact unstable solutions of the underlying equations
    of motion. Using persistent homology, the main tool of topological data analysis
    capturing the persistence across scales of topological features in a point cloud,
    we introduce a method that quantifies visits of turbulent trajectories to unstable
    time-periodic solutions, also called periodic orbits. We demonstrate this method
    first in the Rössler and Kuramoto–Sivashinsky systems. Using this method in 3D
    Kolmogorov flow, we extract a Markov chain from turbulent data, where each node
    corresponds to the neighbourhood of a periodic orbit. The invariant distribution
    of this Markov chain reproduces expectation values on turbulent data when it is
    used to weight averages on the respective periodic orbits.\r\n\r\nIn more realistic,
    wall-bounded settings, such as plane-Couette flow (pcf) driven by the relative
    motion of the walls, or plane-Poiseuille flow (ppf) driven by a pressure gradient,
    finding exact solutions is difficult. We use dynamic mode decomposition (DMD),
    a dimensionality reduction method for sequential data, to identify and approximate
    low-dimensional dynamics without knowing any exact solutions. Most spatially-extended
    systems are equivariant under translations, and in such cases spatial drifts dominate
    DMD, hindering its use in the search for and modelling of low-dimensional dynamics.
    We augment DMD with a symmetry reduction method trained on turbulent data to stop
    it from seeing translations as a feature, improving its ability to extract dynamical
    information in translation-equivariant systems. We find segments of turbulent
    trajectories that linearize well with their symmetry-reduced DMD spectra, akin
    to dynamics near exact solutions. Searching for harmonics in the spectra gives
    leads for periodic orbits with spatial drifts, one of which converges to a new
    solution.\r\n\r\nIn larger domains, turbulence can localize and coexist with surrounding
    laminar flow. Our preceding approaches are global, taking all of a domain into
    account at once, and cannot readily treat each localized patch individually. Working
    first in a minimal oblique domain that can host a single 1D-localized turbulent
    patch, we find that turbulence in ppf is connected to a stable periodic orbit
    at a flow velocity much lower than when turbulence is first onset. We show that,
    well in advance of sustained turbulence, chaos sets in explosively, and for long
    time horizons, time series are consistent with that of a random process.\r\n\r\nFinally,
    in much larger domains, we study and compare 2D-localized turbulence that appears
    as large-scale inclined structures, called stripes, in ppf and pcf. While appearing
    similar, we find that stripes in these two settings differ significantly in terms
    of how they sustain themselves, and in higher velocities, how they proliferate."
acknowledged_ssus:
- _id: ScienComp
acknowledgement: "The work in this thesis was supported by a grant from the Simons
  Foundation (662960, BH).\r\n"
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Gökhan
  full_name: Yalniz, Gökhan
  id: 66E74FA2-D8BF-11E9-8249-8DE2E5697425
  last_name: Yalniz
  orcid: 0000-0002-8490-9312
citation:
  ama: 'Yalniz G. Transition to turbulence : Data-, solution-, and pattern-driven
    approaches. 2025. doi:<a href="https://doi.org/10.15479/AT-ISTA-19684">10.15479/AT-ISTA-19684</a>'
  apa: 'Yalniz, G. (2025). <i>Transition to turbulence : Data-, solution-, and pattern-driven
    approaches</i>. Institute of Science and Technology Austria. <a href="https://doi.org/10.15479/AT-ISTA-19684">https://doi.org/10.15479/AT-ISTA-19684</a>'
  chicago: 'Yalniz, Gökhan. “Transition to Turbulence : Data-, Solution-, and Pattern-Driven
    Approaches.” Institute of Science and Technology Austria, 2025. <a href="https://doi.org/10.15479/AT-ISTA-19684">https://doi.org/10.15479/AT-ISTA-19684</a>.'
  ieee: 'G. Yalniz, “Transition to turbulence : Data-, solution-, and pattern-driven
    approaches,” Institute of Science and Technology Austria, 2025.'
  ista: 'Yalniz G. 2025. Transition to turbulence : Data-, solution-, and pattern-driven
    approaches. Institute of Science and Technology Austria.'
  mla: 'Yalniz, Gökhan. <i>Transition to Turbulence : Data-, Solution-, and Pattern-Driven
    Approaches</i>. Institute of Science and Technology Austria, 2025, doi:<a href="https://doi.org/10.15479/AT-ISTA-19684">10.15479/AT-ISTA-19684</a>.'
  short: 'G. Yalniz, Transition to Turbulence : Data-, Solution-, and Pattern-Driven
    Approaches, Institute of Science and Technology Austria, 2025.'
corr_author: '1'
date_created: 2025-05-12T15:12:28Z
date_published: 2025-05-13T00:00:00Z
date_updated: 2026-06-18T19:23:35Z
day: '13'
ddc:
- '514'
- '519'
- '532'
- '004'
degree_awarded: PhD
department:
- _id: GradSch
- _id: BjHo
doi: 10.15479/AT-ISTA-19684
file:
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  creator: gyalniz
  date_created: 2025-05-12T15:15:59Z
  date_updated: 2025-05-12T15:43:28Z
  description: '3D visualizations of the turbulent flow (left) and the periodic orbits
    (middle) that are being shadowed along with the local state space projections
    (right) onto the principal components of the respective periodic orbit. Shown
    here are the isosurfaces of velocity (red/blue: ±95% of the instantaneous maximum)
    and vorticity (purple/green: ±65% of the instantaneous maximum) in the x-direction.
    Markers along the projections are in sync with the 3D visualizations. The movie
    corresponds to the initial time interval (up to t = 100) of figure 2.2 (a,b);
    periodic orbits and the state space projections are shown only through the shadowing
    events indicated in figure 2.2 (b).'
  file_id: '19686'
  file_name: Movie 2A.1.mp4
  file_size: 37763743
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  creator: gyalniz
  date_created: 2025-05-12T15:16:09Z
  date_updated: 2025-05-12T15:43:28Z
  description: 'Turbulent flow (left) in HKW domain and its symmetry reduction (right).
    Shown here are the isosurfaces of streamwise velocity (red/blue: u = 0.5 max/min
    u) and streamwise vorticity (green/purple: ω_x = 0.5 max/min ω_x).'
  file_id: '19687'
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  content_type: video/mp4
  creator: gyalniz
  date_created: 2025-05-12T15:16:21Z
  date_updated: 2025-05-12T15:43:28Z
  description: 'Turbulent flow (left) in P2K domain and its symmetry reduction (right).
    Shown here are the isosurfaces of streamwise velocity (red/blue: u = 0.5 max/min
    u) and streamwise vorticity (green/purple: ω_x = 0.5 max/min ω_x).'
  file_id: '19688'
  file_name: Movie 3A.2.mp4
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  relation: supplementary_material
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  content_type: video/mp4
  creator: gyalniz
  date_created: 2025-05-12T15:16:36Z
  date_updated: 2025-05-12T15:43:28Z
  description: 'Relative periodic orbit RPO_79.4 (left) of the plane-Couette flow
    (HKW domain) and its symmetry reduction (right). Shown here are the isosurfaces
    of streamwise velocity (red/blue: u = 0.5 max/min u) and streamwise vorticity
    (green/purple: ω_x = 0.5 max/min ω_x).'
  file_id: '19689'
  file_name: Movie 3A.3.mp4
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  content_type: video/mp4
  creator: gyalniz
  date_created: 2025-05-12T15:16:50Z
  date_updated: 2025-05-12T15:43:28Z
  description: 'Symmetry-reduced flow (left), its SRDMD approximation (middle), and
    state space projection (right) showing the spiral-out episode in P2K domain (figure
    3.6 (b) and figure 3.8 (b)). Shown here are the isosurfaces of streamwise velocity
    (red/blue: u = 0.5 max/min u) and streamwise vorticity (green/purple: ω_x = 0.5
    max/min ω_x).'
  file_id: '19690'
  file_name: Movie 3A.4.mp4
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  title: Chapter 3 - Movie 3A.4
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  content_type: video/mp4
  creator: gyalniz
  date_created: 2025-05-12T15:17:11Z
  date_updated: 2025-05-12T15:43:28Z
  description: Movie demonstrating the quasi-steady Reynolds number descent from turbulence
    to a periodic orbit.
  file_id: '19691'
  file_name: Movie 4A.1.mp4
  file_size: 9209327
  relation: supplementary_material
  title: Chapter 4 - Movie 4A.1
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  content_type: video/mp4
  creator: gyalniz
  date_created: 2025-05-12T15:17:43Z
  date_updated: 2025-05-12T15:43:28Z
  description: Streamwise velocity fluctuations (from laminar) of plane-Couette flow
    (Re^C =335) at the y = 0 wall-normal plane in coordinates stationary with respect
    to the bulk velocity. Here, x is the streamwise direction (the wall at y = 1 moves
    to the right) and z is the spanwise direction. Time is in advectime time units.
    Shown is the full (L_x = L_z = 400) domain.
  file_id: '19692'
  file_name: Movie 5A.1.mp4
  file_size: 5893993
  relation: supplementary_material
  title: Chapter 5 - Movie 5A.1
- access_level: open_access
  checksum: fd17eabb70129ceaa414e40924d1d2fe
  content_type: video/mp4
  creator: gyalniz
  date_created: 2025-05-12T15:17:49Z
  date_updated: 2025-05-12T15:43:28Z
  description: Streamwise velocity fluctuations (from laminar) of plane-Poiseuille
    flow (Re^P =660) at the y = 0.5 wall-normal plane in coordinates stationary with
    respect to the bulk velocity. Here, x is the streamwise direction (the mean negative
    pressure gradient is to the right) and z is the spanwise direction. Time is in
    advectime time units. Shown is the full (L_x = L_z = 400) domain.
  file_id: '19693'
  file_name: Movie 5A.2.mp4
  file_size: 3990352
  relation: supplementary_material
  title: Chapter 5 - Movie 5A.2
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  content_type: video/mp4
  creator: gyalniz
  date_created: 2025-05-12T15:17:58Z
  date_updated: 2025-05-12T15:43:28Z
  description: Streamwise velocity fluctuations (from laminar) of plane-Poiseuille
    flow (Re^P=660) at the y = 0.5 wall-normal plane in coordinates stationary with
    respect to the average velocity of the downstream tip of the stripe. Here, x is
    the streamwise direction (the mean negative pressure gradient is to the right)
    and z is the spanwise direction. Time is in advectime time units. Shown is a zoom-in
    of the full (L_x = L_z) domain.
  file_id: '19694'
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  date_created: 2025-05-12T15:27:10Z
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has_accepted_license: '1'
language:
- iso: eng
month: '05'
oa: 1
oa_version: Published Version
page: '155'
project:
- _id: 238598C6-32DE-11EA-91FC-C7463DDC885E
  grant_number: '662960'
  name: Revisiting the Turbulence Problem Using Statistical Mechanics
publication_identifier:
  issn:
  - 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
  record:
  - id: '9558'
    relation: part_of_dissertation
    status: public
  - id: '12105'
    relation: part_of_dissertation
    status: public
  - id: '13274'
    relation: part_of_dissertation
    status: public
  - id: '14466'
    relation: part_of_dissertation
    status: public
  - id: '7563'
    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 : Data-, solution-, and pattern-driven approaches'
type: dissertation
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2025'
...
---
OA_place: publisher
_id: '19906'
abstract:
- lang: eng
  text: "Flows of ordinary fluids such as water or air transition from laminar to
    turbulent\r\nmotion as the velocity increases. This simple dependence of the flow
    state\r\nsolely on inertia, does not apply to more complex substances such as
    polymericand biofluids which commonly have elastic as well as viscous properties.
    Here\r\nvarious different instabilities and turbulent states can arise at low
    and even\r\nvanishing inertia, while high inertia turbulence counterintuitively
    is suppressed\r\nand its drag strongly reduced. We here show in experiments of
    a viscoelastic\r\nmodel fluid that the phenomena observed at low and high inertia
    have a\r\ncommon origin and that the same dynamical state, elasto-inertial turbulence,\r\npersists
    across four orders of magnitude in Reynolds number, ranging from\r\nvery low inertia,
    all the way to high inertia Maximum drag reduction (MDR)\r\nasymptote. We also
    explore the transitions from Newtonian turbulence to\r\nMDR, and specific cases
    of flow at high polymer concentrations, exploring the\r\nrelationship between
    flow at these wide range of control parameters.\r\n"
acknowledged_ssus:
- _id: M-Shop
acknowledgement: "This work was partially funded by the European Union’s Horizon 2020
  research\r\nand innovation programme under the Marie Skłodowska-Curie grant agreement\r\nNo.
  665385."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Sarath S
  full_name: Suresh, Sarath S
  id: 3D126CC4-F248-11E8-B48F-1D18A9856A87
  last_name: Suresh
citation:
  ama: 'Suresh SS. Turbulence in polymeric flows : A characterisation of elasto-inertial
    turbulence and the maximum drag reduction asymptote. 2025. doi:<a href="https://doi.org/10.15479/AT-ISTA-19906">10.15479/AT-ISTA-19906</a>'
  apa: 'Suresh, S. S. (2025). <i>Turbulence in polymeric flows : A characterisation
    of elasto-inertial turbulence and the maximum drag reduction asymptote</i>. Institute
    of Science and Technology Austria. <a href="https://doi.org/10.15479/AT-ISTA-19906">https://doi.org/10.15479/AT-ISTA-19906</a>'
  chicago: 'Suresh, Sarath S. “Turbulence in Polymeric Flows : A Characterisation
    of Elasto-Inertial Turbulence and the Maximum Drag Reduction Asymptote.” Institute
    of Science and Technology Austria, 2025. <a href="https://doi.org/10.15479/AT-ISTA-19906">https://doi.org/10.15479/AT-ISTA-19906</a>.'
  ieee: 'S. S. Suresh, “Turbulence in polymeric flows : A characterisation of elasto-inertial
    turbulence and the maximum drag reduction asymptote,” Institute of Science and
    Technology Austria, 2025.'
  ista: 'Suresh SS. 2025. Turbulence in polymeric flows : A characterisation of elasto-inertial
    turbulence and the maximum drag reduction asymptote. Institute of Science and
    Technology Austria.'
  mla: 'Suresh, Sarath S. <i>Turbulence in Polymeric Flows : A Characterisation of
    Elasto-Inertial Turbulence and the Maximum Drag Reduction Asymptote</i>. Institute
    of Science and Technology Austria, 2025, doi:<a href="https://doi.org/10.15479/AT-ISTA-19906">10.15479/AT-ISTA-19906</a>.'
  short: 'S.S. Suresh, Turbulence in Polymeric Flows : A Characterisation of Elasto-Inertial
    Turbulence and the Maximum Drag Reduction Asymptote, Institute of Science and
    Technology Austria, 2025.'
corr_author: '1'
date_created: 2025-06-26T08:39:08Z
date_published: 2025-06-26T00:00:00Z
date_updated: 2026-04-07T12:39:19Z
day: '26'
ddc:
- '530'
degree_awarded: PhD
department:
- _id: GradSch
- _id: BjHo
doi: 10.15479/AT-ISTA-19906
ec_funded: 1
file:
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  date_created: 2025-06-26T08:41:24Z
  date_updated: 2025-12-27T23:30:02Z
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has_accepted_license: '1'
language:
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license: https://creativecommons.org/licenses/by-nc-sa/4.0/
month: '06'
oa: 1
oa_version: Published Version
page: '82'
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
related_material:
  record:
  - id: '10299'
    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: 'Turbulence in polymeric flows : A characterisation of elasto-inertial turbulence
  and the maximum drag reduction asymptote'
tmp:
  image: /images/cc_by_nc_sa.png
  legal_code_url: https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode
  name: Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC
    BY-NC-SA 4.0)
  short: CC BY-NC-SA (4.0)
type: dissertation
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2025'
...
---
OA_place: publisher
_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:<a
    href="https://doi.org/10.15479/at:ista:12726">10.15479/at:ista:12726</a>
  apa: Riedl, M. (2023). <i>Synchronization in collectively moving active matter</i>.
    Institute of Science and Technology Austria. <a href="https://doi.org/10.15479/at:ista:12726">https://doi.org/10.15479/at:ista:12726</a>
  chicago: Riedl, Michael. “Synchronization in Collectively Moving Active Matter.”
    Institute of Science and Technology Austria, 2023. <a href="https://doi.org/10.15479/at:ista:12726">https://doi.org/10.15479/at:ista:12726</a>.
  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. <i>Synchronization in Collectively Moving Active Matter</i>.
    Institute of Science and Technology Austria, 2023, doi:<a href="https://doi.org/10.15479/at:ista:12726">10.15479/at:ista:12726</a>.
  short: M. Riedl, Synchronization in Collectively Moving Active Matter, Institute
    of Science and Technology Austria, 2023.
corr_author: '1'
date_created: 2023-03-15T13:22:13Z
date_published: 2023-03-23T00:00:00Z
date_updated: 2026-04-07T13:29:13Z
day: '23'
ddc:
- '530'
degree_awarded: PhD
department:
- _id: GradSch
- _id: BjHo
doi: 10.15479/at:ista:12726
file:
- access_level: closed
  checksum: eba0e19fe57a8c15e7aeab55a845efb7
  content_type: application/pdf
  creator: cchlebak
  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.
  file_id: '12745'
  file_name: Thesis_Riedl_2023.pdf
  file_size: 63734746
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  checksum: 0eb7b650cc8ae843bcec7c8a6109ae03
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  creator: cchlebak
  date_created: 2023-03-23T12:54:34Z
  date_updated: 2023-09-24T22:30:03Z
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  file_name: Thesis_Riedl_2023_source.rar
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file_date_updated: 2023-11-24T11:57:46Z
has_accepted_license: '1'
language:
- iso: eng
month: '03'
oa_version: None
page: '260'
publication_identifier:
  issn:
  - 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
  record:
  - id: '461'
    relation: part_of_dissertation
    status: public
  - id: '10791'
    relation: part_of_dissertation
    status: public
  - id: '7932'
    relation: part_of_dissertation
    status: public
  - id: '10703'
    relation: part_of_dissertation
    status: public
  - id: '14530'
    relation: new_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: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2023'
...
---
OA_place: publisher
_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:<a
    href="https://doi.org/10.15479/14530">10.15479/14530</a>
  apa: Riedl, M. (2023). <i>Synchronization in collectively moving active matter</i>.
    Institute of Science and Technology Austria. <a href="https://doi.org/10.15479/14530">https://doi.org/10.15479/14530</a>
  chicago: Riedl, Michael. “Synchronization in Collectively Moving Active Matter.”
    Institute of Science and Technology Austria, 2023. <a href="https://doi.org/10.15479/14530">https://doi.org/10.15479/14530</a>.
  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. <i>Synchronization in Collectively Moving Active Matter</i>.
    Institute of Science and Technology Austria, 2023, doi:<a href="https://doi.org/10.15479/14530">10.15479/14530</a>.
  short: M. Riedl, Synchronization in Collectively Moving Active Matter, Institute
    of Science and Technology Austria, 2023.
corr_author: '1'
date_created: 2023-11-15T09:59:03Z
date_published: 2023-11-16T00:00:00Z
date_updated: 2026-04-07T13:29:13Z
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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  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:
  - 2663-337X
publication_status: published
publisher: Institute of Science and Technology Austria
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    relation: part_of_dissertation
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  - id: '10703'
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    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: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2023'
...
---
OA_place: publisher
_id: '14641'
abstract:
- lang: eng
  text: "Mutation rates represent the net result of complex interactions among various\r\ncellular
    processes and can dramatically influence the evolutionary fate of\r\nmicrobial
    populations. However, many popular techniques used to study\r\nmutations are subject
    to the confounding effects of heredity and the subtleties\r\nof adaptation to
    selection, all of which make it difficult to observe any dynamic\r\nresponses
    of mutation rates to fitness challenges. Furthermore, in spite of the\r\nubiquity
    of quorum sensing systems across the bacterial domain and relevance\r\nfor many
    physiological behaviors, the effects of such mechanisms on mutation\r\nrate and
    adaptation remain poorly understood. In the following work, I\r\npresent the development
    of a microfluidic droplet-based method to measure\r\nsingle base-pair mutation
    rates in growing populations of the bacterium\r\nEscherichia coli. I use this
    method to observe a stress-induced increase in\r\nmutation rate that is mediated
    by luxS, a highly conserved bacterial quorum\r\nsensing component. I also show
    that the aforementioned increase in mutation\r\nrate, and its associated control
    by luxS, corresponds to a higher degree of\r\nadaptability under competitive environments."
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:<a
    href="https://doi.org/10.15479/at:ista:14641">10.15479/at:ista:14641</a>
  apa: Hennessey-Wesen, M. (2023). <i>Adaptive mutation in E. coli modulated by luxS</i>.
    Institute of Science and Technology Austria. <a href="https://doi.org/10.15479/at:ista:14641">https://doi.org/10.15479/at:ista:14641</a>
  chicago: Hennessey-Wesen, Mike. “Adaptive Mutation in E. Coli Modulated by LuxS.”
    Institute of Science and Technology Austria, 2023. <a href="https://doi.org/10.15479/at:ista:14641">https://doi.org/10.15479/at:ista:14641</a>.
  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. <i>Adaptive Mutation in E. Coli Modulated by LuxS</i>.
    Institute of Science and Technology Austria, 2023, doi:<a href="https://doi.org/10.15479/at:ista:14641">10.15479/at:ista:14641</a>.
  short: M. Hennessey-Wesen, Adaptive Mutation in E. Coli Modulated by LuxS, Institute
    of Science and Technology Austria, 2023.
corr_author: '1'
date_created: 2023-12-04T13:17:37Z
date_published: 2023-11-30T00:00:00Z
date_updated: 2026-04-07T13:29:59Z
day: '30'
ddc:
- '570'
degree_awarded: PhD
department:
- _id: GradSch
- _id: BjHo
doi: 10.15479/at:ista:14641
ec_funded: 1
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  embargo_to: open_access
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  file_size: 45847968
  relation: other
  title: Print version
file_date_updated: 2025-07-17T11:20:25Z
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: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2023'
...
---
OA_place: publisher
_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:<a href="https://doi.org/10.15479/at:ista:9728">10.15479/at:ista:9728</a>
  apa: Agrawal, N. (2021). <i>Transition to turbulence and drag reduction in particle-laden
    pipe flows</i>. Institute of Science and Technology Austria. <a href="https://doi.org/10.15479/at:ista:9728">https://doi.org/10.15479/at:ista:9728</a>
  chicago: Agrawal, Nishchal. “Transition to Turbulence and Drag Reduction in Particle-Laden
    Pipe Flows.” Institute of Science and Technology Austria, 2021. <a href="https://doi.org/10.15479/at:ista:9728">https://doi.org/10.15479/at:ista:9728</a>.
  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. <i>Transition to Turbulence and Drag Reduction in Particle-Laden
    Pipe Flows</i>. Institute of Science and Technology Austria, 2021, doi:<a href="https://doi.org/10.15479/at:ista:9728">10.15479/at:ista:9728</a>.
  short: N. Agrawal, Transition to Turbulence and Drag Reduction in Particle-Laden
    Pipe Flows, Institute of Science and Technology Austria, 2021.
corr_author: '1'
date_created: 2021-07-27T13:40:30Z
date_published: 2021-07-29T00:00:00Z
date_updated: 2026-04-16T08:43:20Z
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
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
related_material:
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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: ba8df636-2132-11f1-aed0-ed93e2281fdd
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:<a href="https://doi.org/10.15479/AT:ISTA:8350">10.15479/AT:ISTA:8350</a>
  apa: Shamipour, S. (2020). <i>Bulk actin dynamics drive phase segregation in zebrafish
    oocytes </i>. Institute of Science and Technology Austria. <a href="https://doi.org/10.15479/AT:ISTA:8350">https://doi.org/10.15479/AT:ISTA:8350</a>
  chicago: Shamipour, Shayan. “Bulk Actin Dynamics Drive Phase Segregation in Zebrafish
    Oocytes .” Institute of Science and Technology Austria, 2020. <a href="https://doi.org/10.15479/AT:ISTA:8350">https://doi.org/10.15479/AT:ISTA:8350</a>.
  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. <i>Bulk Actin Dynamics Drive Phase Segregation in Zebrafish
    Oocytes </i>. Institute of Science and Technology Austria, 2020, doi:<a href="https://doi.org/10.15479/AT:ISTA:8350">10.15479/AT:ISTA:8350</a>.
  short: S. Shamipour, Bulk Actin Dynamics Drive Phase Segregation in Zebrafish Oocytes
    , Institute of Science and Technology Austria, 2020.
corr_author: '1'
date_created: 2020-09-09T11:12:10Z
date_published: 2020-09-09T00:00:00Z
date_updated: 2025-09-11T07:08:52Z
day: '09'
ddc:
- '570'
degree_awarded: PhD
department:
- _id: BjHo
- _id: CaHe
doi: 10.15479/AT:ISTA:8350
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- 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: 2DF688A6-F248-11E8-B48F-1D18A9856A87
year: '2020'
...
---
OA_place: publisher
_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:<a href="https://doi.org/10.15479/AT:ISTA:7258">10.15479/AT:ISTA:7258</a>
  apa: Scarselli, D. (2020). <i>New approaches to reduce friction in turbulent pipe
    flow</i>. Institute of Science and Technology Austria. <a href="https://doi.org/10.15479/AT:ISTA:7258">https://doi.org/10.15479/AT:ISTA:7258</a>
  chicago: Scarselli, Davide. “New Approaches to Reduce Friction in Turbulent Pipe
    Flow.” Institute of Science and Technology Austria, 2020. <a href="https://doi.org/10.15479/AT:ISTA:7258">https://doi.org/10.15479/AT:ISTA:7258</a>.
  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. <i>New Approaches to Reduce Friction in Turbulent Pipe Flow</i>.
    Institute of Science and Technology Austria, 2020, doi:<a href="https://doi.org/10.15479/AT:ISTA:7258">10.15479/AT:ISTA:7258</a>.
  short: D. Scarselli, New Approaches to Reduce Friction in Turbulent Pipe Flow, Institute
    of Science and Technology Austria, 2020.
corr_author: '1'
date_created: 2020-01-12T16:07:26Z
date_published: 2020-01-13T00:00:00Z
date_updated: 2026-04-08T07:28:22Z
day: '13'
ddc:
- '532'
degree_awarded: PhD
department:
- _id: BjHo
doi: 10.15479/AT:ISTA:7258
ec_funded: 1
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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
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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: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2020'
...
---
OA_place: publisher
_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:<a href="https://doi.org/10.15479/AT:ISTA:6957">10.15479/AT:ISTA:6957</a>
  apa: Paranjape, C. S. (2019). <i>Onset of turbulence in plane Poiseuille flow</i>.
    Institute of Science and Technology Austria. <a href="https://doi.org/10.15479/AT:ISTA:6957">https://doi.org/10.15479/AT:ISTA:6957</a>
  chicago: Paranjape, Chaitanya S. “Onset of Turbulence in Plane Poiseuille Flow.”
    Institute of Science and Technology Austria, 2019. <a href="https://doi.org/10.15479/AT:ISTA:6957">https://doi.org/10.15479/AT:ISTA:6957</a>.
  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. <i>Onset of Turbulence in Plane Poiseuille Flow</i>.
    Institute of Science and Technology Austria, 2019, doi:<a href="https://doi.org/10.15479/AT:ISTA:6957">10.15479/AT:ISTA:6957</a>.
  short: C.S. Paranjape, Onset of Turbulence in Plane Poiseuille Flow, Institute of
    Science and Technology Austria, 2019.
corr_author: '1'
date_created: 2019-10-22T12:08:43Z
date_published: 2019-10-24T00:00:00Z
date_updated: 2026-04-08T07:46:58Z
day: '24'
ddc:
- '532'
degree_awarded: PhD
department:
- _id: BjHo
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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
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- 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: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2019'
...