---
_id: '14466'
abstract:
- lang: eng
text: The first long-lived turbulent structures observable in planar shear flows
take the form of localized stripes, inclined with respect to the mean flow direction.
The dynamics of these stripes is central to transition, and recent studies proposed
an analogy to directed percolation where the stripes’ proliferation is ultimately
responsible for the turbulence becoming sustained. In the present study we focus
on the internal stripe dynamics as well as on the eventual stripe expansion, and
we compare the underlying mechanisms in pressure- and shear-driven planar flows,
respectively, plane-Poiseuille and plane-Couette flow. Despite the similarities
of the overall laminar–turbulence patterns, the stripe proliferation processes
in the two cases are fundamentally different. Starting from the growth and sustenance
of individual stripes, we find that in plane-Couette flow new streaks are created
stochastically throughout the stripe whereas in plane-Poiseuille flow streak creation
is deterministic and occurs locally at the downstream tip. Because of the up/downstream
symmetry, Couette stripes, in contrast to Poiseuille stripes, have two weak and
two strong laminar turbulent interfaces. These differences in symmetry as well
as in internal growth give rise to two fundamentally different stripe splitting
mechanisms. In plane-Poiseuille flow splitting is connected to the elongational
growth of the original stripe, and it results from a break-off/shedding of the
stripe's tail. In plane-Couette flow splitting follows from a broadening of the
original stripe and a division along the stripe into two slimmer stripes.
acknowledgement: E.M. acknowledges funding from the ISTplus fellowship programme.
G.Y. and B.H. acknowledge a grant from the Simons Foundation (662960, BH).
article_number: A21
article_processing_charge: Yes (via OA deal)
article_type: original
arxiv: 1
author:
- first_name: Elena
full_name: Marensi, Elena
id: 0BE7553A-1004-11EA-B805-18983DDC885E
last_name: Marensi
orcid: 0000-0001-7173-4923
- first_name: Gökhan
full_name: Yalniz, Gökhan
id: 66E74FA2-D8BF-11E9-8249-8DE2E5697425
last_name: Yalniz
orcid: 0000-0002-8490-9312
- first_name: Björn
full_name: Hof, Björn
id: 3A374330-F248-11E8-B48F-1D18A9856A87
last_name: Hof
orcid: 0000-0003-2057-2754
citation:
ama: Marensi E, Yalniz G, Hof B. Dynamics and proliferation of turbulent stripes
in plane-Poiseuille and plane-Couette flows. Journal of Fluid Mechanics.
2023;974. doi:10.1017/jfm.2023.780
apa: Marensi, E., Yalniz, G., & Hof, B. (2023). Dynamics and proliferation of
turbulent stripes in plane-Poiseuille and plane-Couette flows. Journal of Fluid
Mechanics. Cambridge University Press. https://doi.org/10.1017/jfm.2023.780
chicago: Marensi, Elena, Gökhan Yalniz, and Björn Hof. “Dynamics and Proliferation
of Turbulent Stripes in Plane-Poiseuille and Plane-Couette Flows.” Journal
of Fluid Mechanics. Cambridge University Press, 2023. https://doi.org/10.1017/jfm.2023.780.
ieee: E. Marensi, G. Yalniz, and B. Hof, “Dynamics and proliferation of turbulent
stripes in plane-Poiseuille and plane-Couette flows,” Journal of Fluid Mechanics,
vol. 974. Cambridge University Press, 2023.
ista: Marensi E, Yalniz G, Hof B. 2023. Dynamics and proliferation of turbulent
stripes in plane-Poiseuille and plane-Couette flows. Journal of Fluid Mechanics.
974, A21.
mla: Marensi, Elena, et al. “Dynamics and Proliferation of Turbulent Stripes in
Plane-Poiseuille and Plane-Couette Flows.” Journal of Fluid Mechanics,
vol. 974, A21, Cambridge University Press, 2023, doi:10.1017/jfm.2023.780.
short: E. Marensi, G. Yalniz, B. Hof, Journal of Fluid Mechanics 974 (2023).
date_created: 2023-10-30T09:32:28Z
date_published: 2023-11-10T00:00:00Z
date_updated: 2024-02-15T09:06:23Z
day: '10'
ddc:
- '530'
department:
- _id: GradSch
- _id: BjHo
doi: 10.1017/jfm.2023.780
external_id:
arxiv:
- '2212.12406'
isi:
- '001088363700001'
file:
- access_level: open_access
checksum: 17c64c1fb0d5f73252364bf98b0b9e1a
content_type: application/pdf
creator: dernst
date_created: 2024-02-15T09:05:21Z
date_updated: 2024-02-15T09:05:21Z
file_id: '14996'
file_name: 2023_JourFluidMechanics_Marensi.pdf
file_size: 2804641
relation: main_file
success: 1
file_date_updated: 2024-02-15T09:05:21Z
has_accepted_license: '1'
intvolume: ' 974'
isi: 1
keyword:
- turbulence
- transition to turbulence
- patterns
language:
- iso: eng
month: '11'
oa: 1
oa_version: Published Version
project:
- _id: 238598C6-32DE-11EA-91FC-C7463DDC885E
grant_number: '662960'
name: 'Revisiting the Turbulence Problem Using Statistical Mechanics: Experimental
Studies on Transitional and Turbulent Flows'
publication: Journal of Fluid Mechanics
publication_identifier:
eissn:
- 1469-7645
issn:
- 0022-1120
publication_status: published
publisher: Cambridge University Press
quality_controlled: '1'
status: public
title: Dynamics and proliferation of turbulent stripes in plane-Poiseuille and plane-Couette
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: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 974
year: '2023'
...
---
_id: '11609'
abstract:
- lang: eng
text: "Context. Stellar interiors are the seat of efficient transport of angular
momentum all along their evolution. In this context, understanding the dependence
of the turbulent transport triggered by the instabilities of the vertical and
horizontal shears of the differential rotation in stellar radiation zones as a
function of their rotation, stratification, and thermal diffusivity is mandatory.
Indeed, it constitutes one of the cornerstones of the rotational transport and
mixing theory, which is implemented in stellar evolution codes to predict the
rotational and chemical evolutions of stars.\r\n\r\nAims. We investigate horizontal
shear instabilities in rotating stellar radiation zones by considering the full
Coriolis acceleration with both the dimensionless horizontal Coriolis component
f̃ and the vertical component f.\r\n\r\nMethods. We performed a linear stability
analysis using linearized equations derived from the Navier-Stokes and heat transport
equations in the rotating nontraditional f-plane. We considered a horizontal shear
flow with a hyperbolic tangent profile as the base flow. The linear stability
was analyzed numerically in wide ranges of parameters, and we performed an asymptotic
analysis for large vertical wavenumbers using the Wentzel-Kramers-Brillouin-Jeffreys
(WKBJ) approximation for nondiffusive and highly-diffusive fluids.\r\n\r\nResults.
As in the traditional f-plane approximation, we identify two types of instabilities:
the inflectional and inertial instabilities. The inflectional instability is destabilized
as f̃ increases and its maximum growth rate increases significantly, while the
thermal diffusivity stabilizes the inflectional instability similarly to the traditional
case. The inertial instability is also strongly affected; for instance, the inertially
unstable regime is also extended in the nondiffusive limit as 0 < f < 1 + f̃ 2/N2,
where N is the dimensionless Brunt-Väisälä frequency. More strikingly, in the
high thermal diffusivity limit, it is always inertially unstable at any colatitude
θ except at the poles (i.e., 0° < θ < 180°). We also derived the critical Reynolds
numbers for the inertial instability using the asymptotic dispersion relations
obtained from the WKBJ analysis. Using the asymptotic and numerical results, we
propose a prescription for the effective turbulent viscosities induced by the
inertial and inflectional instabilities that can be possibly used in stellar evolution
models. The characteristic time of this turbulence is short enough so that it
is efficient to redistribute angular momentum and to mix chemicals in stellar
radiation zones."
acknowledgement: The authors acknowledge support from the European Research Council
through ERC grant SPIRE 647383 and from GOLF and PLATO CNES grants at the Department
of Astrophysics at CEA Paris-Saclay. We thank the referee, Prof. A. J. Barker, for
his constructive comments that allow us to improve the article.
article_number: A64
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: J.
full_name: Park, J.
last_name: Park
- first_name: V.
full_name: Prat, V.
last_name: Prat
- first_name: S.
full_name: Mathis, S.
last_name: Mathis
- first_name: Lisa Annabelle
full_name: Bugnet, Lisa Annabelle
id: d9edb345-f866-11ec-9b37-d119b5234501
last_name: Bugnet
orcid: 0000-0003-0142-4000
citation:
ama: 'Park J, Prat V, Mathis S, Bugnet LA. Horizontal shear instabilities in rotating
stellar radiation zones: II. Effects of the full Coriolis acceleration. Astronomy
& Astrophysics. 2021;646. doi:10.1051/0004-6361/202038654'
apa: 'Park, J., Prat, V., Mathis, S., & Bugnet, L. A. (2021). Horizontal shear
instabilities in rotating stellar radiation zones: II. Effects of the full Coriolis
acceleration. Astronomy & Astrophysics. EDP Sciences. https://doi.org/10.1051/0004-6361/202038654'
chicago: 'Park, J., V. Prat, S. Mathis, and Lisa Annabelle Bugnet. “Horizontal Shear
Instabilities in Rotating Stellar Radiation Zones: II. Effects of the Full Coriolis
Acceleration.” Astronomy & Astrophysics. EDP Sciences, 2021. https://doi.org/10.1051/0004-6361/202038654.'
ieee: 'J. Park, V. Prat, S. Mathis, and L. A. Bugnet, “Horizontal shear instabilities
in rotating stellar radiation zones: II. Effects of the full Coriolis acceleration,”
Astronomy & Astrophysics, vol. 646. EDP Sciences, 2021.'
ista: 'Park J, Prat V, Mathis S, Bugnet LA. 2021. Horizontal shear instabilities
in rotating stellar radiation zones: II. Effects of the full Coriolis acceleration.
Astronomy & Astrophysics. 646, A64.'
mla: 'Park, J., et al. “Horizontal Shear Instabilities in Rotating Stellar Radiation
Zones: II. Effects of the Full Coriolis Acceleration.” Astronomy & Astrophysics,
vol. 646, A64, EDP Sciences, 2021, doi:10.1051/0004-6361/202038654.'
short: J. Park, V. Prat, S. Mathis, L.A. Bugnet, Astronomy & Astrophysics 646
(2021).
date_created: 2022-07-18T13:24:32Z
date_published: 2021-02-08T00:00:00Z
date_updated: 2022-08-19T10:18:03Z
day: '08'
doi: 10.1051/0004-6361/202038654
extern: '1'
external_id:
arxiv:
- '2006.10660'
intvolume: ' 646'
keyword:
- Space and Planetary Science
- Astronomy and Astrophysics
- hydrodynamics / turbulence / stars
- rotation / stars
- evolution
language:
- iso: eng
main_file_link:
- open_access: '1'
url: https://arxiv.org/abs/2006.10660
month: '02'
oa: 1
oa_version: Preprint
publication: Astronomy & Astrophysics
publication_identifier:
eissn:
- 1432-0746
issn:
- 0004-6361
publication_status: published
publisher: EDP Sciences
quality_controlled: '1'
scopus_import: '1'
status: public
title: 'Horizontal shear instabilities in rotating stellar radiation zones: II. Effects
of the full Coriolis acceleration'
type: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 646
year: '2021'
...
---
_id: '10299'
abstract:
- lang: eng
text: Turbulence generally arises in shear flows if velocities and hence, inertial
forces are sufficiently large. In striking contrast, viscoelastic fluids can exhibit
disordered motion even at vanishing inertia. Intermediate between these cases,
a state of chaotic motion, “elastoinertial turbulence” (EIT), has been observed
in a narrow Reynolds number interval. We here determine the origin of EIT in experiments
and show that characteristic EIT structures can be detected across an unexpectedly
wide range of parameters. Close to onset, a pattern of chevron-shaped streaks
emerges in qualitative agreement with linear and weakly nonlinear theory. However,
in experiments, the dynamics remain weakly chaotic, and the instability can be
traced to far lower Reynolds numbers than permitted by theory. For increasing
inertia, the flow undergoes a transformation to a wall mode composed of inclined
near-wall streaks and shear layers. This mode persists to what is known as the
“maximum drag reduction limit,” and overall EIT is found to dominate viscoelastic
flows across more than three orders of magnitude in Reynolds number.
acknowledgement: We thank Y. Dubief, R. Kerswell, E. Marensi, V. Shankar, V. Steinberg,
and V. Terrapon for discussions and helpful comments. A.V. and B.H. acknowledge
funding from the Austrian Science Fund, grant I4188-N30, within the Deutsche Forschungsgemeinschaft
research unit FOR 2688.
article_number: e2102350118
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: George H
full_name: Choueiri, George H
id: 448BD5BC-F248-11E8-B48F-1D18A9856A87
last_name: Choueiri
- first_name: Jose M
full_name: Lopez Alonso, Jose M
id: 40770848-F248-11E8-B48F-1D18A9856A87
last_name: Lopez Alonso
orcid: 0000-0002-0384-2022
- first_name: Atul
full_name: Varshney, Atul
id: 2A2006B2-F248-11E8-B48F-1D18A9856A87
last_name: Varshney
orcid: 0000-0002-3072-5999
- first_name: Sarath
full_name: Sankar, Sarath
last_name: Sankar
- first_name: Björn
full_name: Hof, Björn
id: 3A374330-F248-11E8-B48F-1D18A9856A87
last_name: Hof
orcid: 0000-0003-2057-2754
citation:
ama: Choueiri GH, Lopez Alonso JM, Varshney A, Sankar S, Hof B. Experimental observation
of the origin and structure of elastoinertial turbulence. Proceedings of the
National Academy of Sciences. 2021;118(45). doi:10.1073/pnas.2102350118
apa: Choueiri, G. H., Lopez Alonso, J. M., Varshney, A., Sankar, S., & Hof,
B. (2021). Experimental observation of the origin and structure of elastoinertial
turbulence. Proceedings of the National Academy of Sciences. National Academy
of Sciences. https://doi.org/10.1073/pnas.2102350118
chicago: Choueiri, George H, Jose M Lopez Alonso, Atul Varshney, Sarath Sankar,
and Björn Hof. “Experimental Observation of the Origin and Structure of Elastoinertial
Turbulence.” Proceedings of the National Academy of Sciences. National
Academy of Sciences, 2021. https://doi.org/10.1073/pnas.2102350118.
ieee: G. H. Choueiri, J. M. Lopez Alonso, A. Varshney, S. Sankar, and B. Hof, “Experimental
observation of the origin and structure of elastoinertial turbulence,” Proceedings
of the National Academy of Sciences, vol. 118, no. 45. National Academy of
Sciences, 2021.
ista: Choueiri GH, Lopez Alonso JM, Varshney A, Sankar S, Hof B. 2021. Experimental
observation of the origin and structure of elastoinertial turbulence. Proceedings
of the National Academy of Sciences. 118(45), e2102350118.
mla: Choueiri, George H., et al. “Experimental Observation of the Origin and Structure
of Elastoinertial Turbulence.” Proceedings of the National Academy of Sciences,
vol. 118, no. 45, e2102350118, National Academy of Sciences, 2021, doi:10.1073/pnas.2102350118.
short: G.H. Choueiri, J.M. Lopez Alonso, A. Varshney, S. Sankar, B. Hof, Proceedings
of the National Academy of Sciences 118 (2021).
date_created: 2021-11-17T13:24:24Z
date_published: 2021-11-03T00:00:00Z
date_updated: 2023-08-14T11:50:10Z
day: '03'
department:
- _id: BjHo
doi: 10.1073/pnas.2102350118
external_id:
arxiv:
- '2103.00023'
isi:
- '000720926900019'
pmid:
- ' 34732570'
intvolume: ' 118'
isi: 1
issue: '45'
keyword:
- multidisciplinary
- elastoinertial turbulence
- viscoelastic flows
- elastic instability
- drag reduction
language:
- iso: eng
main_file_link:
- open_access: '1'
url: https://arxiv.org/abs/2103.00023
month: '11'
oa: 1
oa_version: Preprint
pmid: 1
project:
- _id: 238B8092-32DE-11EA-91FC-C7463DDC885E
call_identifier: FWF
grant_number: I04188
name: Instabilities in pulsating pipe flow of Newtonian and complex fluids
publication: Proceedings of the National Academy of Sciences
publication_identifier:
eissn:
- 1091-6490
issn:
- 0027-8424
publication_status: published
publisher: National Academy of Sciences
quality_controlled: '1'
scopus_import: '1'
status: public
title: Experimental observation of the origin and structure of elastoinertial turbulence
type: journal_article
user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8
volume: 118
year: '2021'
...
---
_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
file:
- access_level: closed
checksum: 77436be3563a90435024307b1b5ee7e8
content_type: application/x-zip-compressed
creator: nagrawal
date_created: 2021-07-28T13:32:02Z
date_updated: 2022-07-29T22:30:05Z
embargo_to: open_access
file_id: '9744'
file_name: Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows.zip
file_size: 22859658
relation: source_file
- access_level: open_access
checksum: 72a891d7daba85445c29b868c22575ed
content_type: application/pdf
creator: nagrawal
date_created: 2021-07-28T13:32:05Z
date_updated: 2022-07-29T22:30:05Z
embargo: 2022-07-28
file_id: '9745'
file_name: Transition to Turbulence and Drag Reduction in Particle-Laden Pipe Flows.pdf
file_size: 18658048
relation: main_file
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:
record:
- id: '6189'
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: '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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checksum: 7ba298ba0ce7e1d11691af6b8eaf0a0a
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creator: cparanjape
date_created: 2019-10-23T09:54:43Z
date_updated: 2020-07-14T12:47:46Z
file_id: '6962'
file_name: Chaitanya_Paranjape_source_files_tex_figures.zip
file_size: 45828099
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checksum: 642697618314e31ac31392da7909c2d9
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creator: cparanjape
date_created: 2019-10-23T10:37:09Z
date_updated: 2020-07-14T12:47:46Z
file_id: '6963'
file_name: Chaitanya_Paranjape_Thesis.pdf
file_size: 19504197
relation: main_file
file_date_updated: 2020-07-14T12:47:46Z
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'
...