---
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: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.
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
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: ba8df636-2132-11f1-aed0-ed93e2281fdd
year: '2021'
...
---
OA_place: repository
OA_type: green
_id: '22433'
abstract:
- lang: eng
text: 'Process-based hydrological models have a long history dating back to the
1960s. Criticized by some as over-parameterized, overly complex, and difficult
to use, a more nuanced view is that these tools are necessary in many situations
and, in a certain class of problems, they are the most appropriate type of hydrological
model. This is especially the case in situations where knowledge of flow paths
or distributed state variables and/or preservation of physical constraints is
important. Examples of this include: spatiotemporal variability of soil moisture,
groundwater flow and runoff generation, sediment and contaminant transport, or
when feedbacks among various Earth’s system processes or understanding the impacts
of climate non-stationarity are of primary concern. These are situations where
process-based models excel and other models are unverifiable. This article presents
this pragmatic view in the context of existing literature to justify the approach
where applicable and necessary. We review how improvements in data availability,
computational resources and algorithms have made detailed hydrological simulations
a reality. Avenues for the future of process-based hydrological models are presented
suggesting their use as virtual laboratories, for design purposes, and with a
powerful treatment of uncertainty.'
article_processing_charge: No
article_type: original
author:
- first_name: Simone
full_name: Fatichi, Simone
id: cf8e546b-a9b0-11f0-a43b-aa89ed1b56d6
last_name: Fatichi
- first_name: Enrique R.
full_name: Vivoni, Enrique R.
last_name: Vivoni
- first_name: Fred L.
full_name: Ogden, Fred L.
last_name: Ogden
- first_name: Valeriy Y.
full_name: Ivanov, Valeriy Y.
last_name: Ivanov
- first_name: Benjamin
full_name: Mirus, Benjamin
last_name: Mirus
- first_name: David
full_name: Gochis, David
last_name: Gochis
- first_name: Charles W.
full_name: Downer, Charles W.
last_name: Downer
- first_name: Matteo
full_name: Camporese, Matteo
last_name: Camporese
- first_name: Jason H.
full_name: Davison, Jason H.
last_name: Davison
- first_name: Brian
full_name: Ebel, Brian
last_name: Ebel
- first_name: Norm
full_name: Jones, Norm
last_name: Jones
- first_name: Jongho
full_name: Kim, Jongho
last_name: Kim
- first_name: Giuseppe
full_name: Mascaro, Giuseppe
last_name: Mascaro
- first_name: Richard
full_name: Niswonger, Richard
last_name: Niswonger
- first_name: Pedro
full_name: Restrepo, Pedro
last_name: Restrepo
- first_name: Riccardo
full_name: Rigon, Riccardo
last_name: Rigon
- first_name: Chaopeng
full_name: Shen, Chaopeng
last_name: Shen
- first_name: Mauro
full_name: Sulis, Mauro
last_name: Sulis
- first_name: David
full_name: Tarboton, David
last_name: Tarboton
citation:
ama: Fatichi S, Vivoni ER, Ogden FL, et al. An overview of current applications,
challenges, and future trends in distributed process-based models in hydrology.
Journal of Hydrology. 2016;537:45-60. doi:10.1016/j.jhydrol.2016.03.026
apa: Fatichi, S., Vivoni, E. R., Ogden, F. L., Ivanov, V. Y., Mirus, B., Gochis,
D., … Tarboton, D. (2016). An overview of current applications, challenges, and
future trends in distributed process-based models in hydrology. Journal of
Hydrology. Elsevier. https://doi.org/10.1016/j.jhydrol.2016.03.026
chicago: Fatichi, Simone, Enrique R. Vivoni, Fred L. Ogden, Valeriy Y. Ivanov, Benjamin
Mirus, David Gochis, Charles W. Downer, et al. “An Overview of Current Applications,
Challenges, and Future Trends in Distributed Process-Based Models in Hydrology.”
Journal of Hydrology. Elsevier, 2016. https://doi.org/10.1016/j.jhydrol.2016.03.026.
ieee: S. Fatichi et al., “An overview of current applications, challenges,
and future trends in distributed process-based models in hydrology,” Journal
of Hydrology, vol. 537. Elsevier, pp. 45–60, 2016.
ista: Fatichi S, Vivoni ER, Ogden FL, Ivanov VY, Mirus B, Gochis D, Downer CW, Camporese
M, Davison JH, Ebel B, Jones N, Kim J, Mascaro G, Niswonger R, Restrepo P, Rigon
R, Shen C, Sulis M, Tarboton D. 2016. An overview of current applications, challenges,
and future trends in distributed process-based models in hydrology. Journal of
Hydrology. 537, 45–60.
mla: Fatichi, Simone, et al. “An Overview of Current Applications, Challenges, and
Future Trends in Distributed Process-Based Models in Hydrology.” Journal of
Hydrology, vol. 537, Elsevier, 2016, pp. 45–60, doi:10.1016/j.jhydrol.2016.03.026.
short: S. Fatichi, E.R. Vivoni, F.L. Ogden, V.Y. Ivanov, B. Mirus, D. Gochis, C.W.
Downer, M. Camporese, J.H. Davison, B. Ebel, N. Jones, J. Kim, G. Mascaro, R.
Niswonger, P. Restrepo, R. Rigon, C. Shen, M. Sulis, D. Tarboton, Journal of Hydrology
537 (2016) 45–60.
das_tickbox: '1'
date_created: 2026-07-27T12:30:23Z
date_published: 2016-06-01T00:00:00Z
date_updated: 2026-08-11T06:17:23Z
day: '01'
doi: 10.1016/j.jhydrol.2016.03.026
extern: '1'
intvolume: ' 537'
keyword:
- Modeling
- Interdisciplinary
- Watershed processes
- Virtual experiments
- Change assessments
- Natural and built environment
language:
- iso: eng
main_file_link:
- open_access: '1'
url: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3459&context=cee_facpub
month: '06'
oa: 1
oa_version: Accepted Version
page: 45-60
publication: Journal of Hydrology
publication_identifier:
eissn:
- 1879-2707
issn:
- 0022-1694
publication_status: published
publisher: Elsevier
quality_controlled: '1'
scopus_import: '1'
status: public
title: An overview of current applications, challenges, and future trends in distributed
process-based models in hydrology
tmp:
image: /images/cc_by_nc_nd.png
legal_code_url: https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode
name: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
(CC BY-NC-ND 4.0)
short: CC BY-NC-ND (4.0)
type: journal_article
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
volume: 537
year: '2016'
...
---
OA_type: closed access
_id: '22476'
abstract:
- lang: eng
text: Projections of the future carbon and water cycles rely on knowledge on how
forests will respond to rising atmospheric CO2. Experiments with elevated CO2
are logistically challenging and carbon pools and fluxes are difficult to measure
and upscale due to their spatiotemporal heterogeneity. Therefore, it is important
to combine the knowledge derived from experimental results with modeling. Here,
we systematically compare data from a free air CO2 enrichment (FACE) experiment
in a mature deciduous forest in Switzerland with realizations from an ecohydrological
model (Tethys–Chloris). We test whether a mechanistic ecohydrological model is
able to simulate physiological plant responses under ambient and elevated CO2
concentration. We overcome measurement limitations by quantifying differences
in response to ambient and elevated CO2 over ten years. The reliability of model
realizations is demonstrated by comparing simulations with field observations
of stomatal conductance, sap flow, leaf and fruit litter, and stem growth. The
model successfully captures the observed CO2-induced difference in stomatal conductance
and transpiration and its sensitivity to atmospheric demand, as well as qualitative
changes in soil moisture. The simulated differences between CO2 scenarios generally
fall within the uncertainty of experimental observations, both for the carbon
and water balance. Simulated total evapotranspiration is 2.8% (18 mm yr−1) lower
and soil moisture 1.2% higher in the CO2-enriched scenario. Latent and sensible
heat are modified by ca. 1 W m−2. Net primary production is simulated to increase
by 19.8% and allocation to stem growth is 53 gC yr−1 m−2 higher in the elevated
CO2 scenario, which represents the limit of the detection threshold of the experiment.
Results show that while ecohydrological models can be used to reliably simulate
multi-year energy, water, and carbon fluxes at the stand level, testing carbon
allocation remains critical with current accuracy of field measurements. Uncertainties
due to the simplified carbon allocation scheme are shown to be more significant
for carbon than for energy and water fluxes. Generally, we conclude that for this
type of forest, differences in annual energy and water fluxes induced by elevated
CO2 are likely to be less than 10%.
article_processing_charge: No
article_type: original
author:
- first_name: Simone
full_name: Fatichi, Simone
id: cf8e546b-a9b0-11f0-a43b-aa89ed1b56d6
last_name: Fatichi
- first_name: Sebastian
full_name: Leuzinger, Sebastian
last_name: Leuzinger
citation:
ama: 'Fatichi S, Leuzinger S. Reconciling observations with modeling: The fate of
water and carbon allocation in a mature deciduous forest exposed to elevated CO2.
Agricultural and Forest Meteorology. 2013;174-175:144-157. doi:10.1016/j.agrformet.2013.02.005'
apa: 'Fatichi, S., & Leuzinger, S. (2013). Reconciling observations with modeling:
The fate of water and carbon allocation in a mature deciduous forest exposed to
elevated CO2. Agricultural and Forest Meteorology. Elsevier. https://doi.org/10.1016/j.agrformet.2013.02.005'
chicago: 'Fatichi, Simone, and Sebastian Leuzinger. “Reconciling Observations with
Modeling: The Fate of Water and Carbon Allocation in a Mature Deciduous Forest
Exposed to Elevated CO2.” Agricultural and Forest Meteorology. Elsevier,
2013. https://doi.org/10.1016/j.agrformet.2013.02.005.'
ieee: 'S. Fatichi and S. Leuzinger, “Reconciling observations with modeling: The
fate of water and carbon allocation in a mature deciduous forest exposed to elevated
CO2,” Agricultural and Forest Meteorology, vol. 174–175. Elsevier, pp.
144–157, 2013.'
ista: 'Fatichi S, Leuzinger S. 2013. Reconciling observations with modeling: The
fate of water and carbon allocation in a mature deciduous forest exposed to elevated
CO2. Agricultural and Forest Meteorology. 174–175, 144–157.'
mla: 'Fatichi, Simone, and Sebastian Leuzinger. “Reconciling Observations with Modeling:
The Fate of Water and Carbon Allocation in a Mature Deciduous Forest Exposed to
Elevated CO2.” Agricultural and Forest Meteorology, vol. 174–175, Elsevier,
2013, pp. 144–57, doi:10.1016/j.agrformet.2013.02.005.'
short: S. Fatichi, S. Leuzinger, Agricultural and Forest Meteorology 174–175 (2013)
144–157.
das_tickbox: '1'
date_created: 2026-07-27T12:30:23Z
date_published: 2013-06-15T00:00:00Z
date_updated: 2026-08-12T13:59:36Z
day: '15'
doi: 10.1016/j.agrformet.2013.02.005
extern: '1'
keyword:
- Ecohydrological modeling
- Plant water relations
- FACE experiments
- Forest productivity
- CO2 enrichment
- Swiss Canopy Crane
language:
- iso: eng
month: '06'
oa_version: None
page: 144-157
publication: Agricultural and Forest Meteorology
publication_identifier:
eissn:
- 1873-2240
issn:
- 0168-1923
publication_status: published
publisher: Elsevier
quality_controlled: '1'
scopus_import: '1'
status: public
title: 'Reconciling observations with modeling: The fate of water and carbon allocation
in a mature deciduous forest exposed to elevated CO2'
type: journal_article
user_id: ba8df636-2132-11f1-aed0-ed93e2281fdd
volume: 174-175
year: '2013'
...