---
_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.
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'
...