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Spontaneous concentrations of solids through two-way drag forces between gas and sedimenting particles

Lambrechts, M. LU ; Johansen, A. LU ; Capelo, H. L.; Blum, J. and Bodenschatz, E. (2016) In Astronomy and Astrophysics 591.
Abstract

The behaviour of sedimenting particles depends on the dust-to-gas ratio of the fluid. Linear stability analysis shows that solids settling in the Epstein drag regime would remain homogeneously distributed in non-rotating incompressible fluids, even when dust-to-gas ratios reach unity. However, the nonlinear evolution has not been probed before. Here, we present numerical calculations indicating that, in a particle-dense mixture, solids spontaneously mix out of the fluid and form swarms that are overdense in particles by at least a factor 10. The instability is caused by mass-loaded regions locally breaking the equilibrium background stratification. The driving mechanism depends on nonlinear perturbations of the background flow and... (More)

The behaviour of sedimenting particles depends on the dust-to-gas ratio of the fluid. Linear stability analysis shows that solids settling in the Epstein drag regime would remain homogeneously distributed in non-rotating incompressible fluids, even when dust-to-gas ratios reach unity. However, the nonlinear evolution has not been probed before. Here, we present numerical calculations indicating that, in a particle-dense mixture, solids spontaneously mix out of the fluid and form swarms that are overdense in particles by at least a factor 10. The instability is caused by mass-loaded regions locally breaking the equilibrium background stratification. The driving mechanism depends on nonlinear perturbations of the background flow and shares some similarity to the streaming instability in accretion discs. The resulting particle-rich swarms may stimulate particle growth by coagulation. In the context of protoplanetary discs, the instability could be relevant for aiding small particles to settle to the midplane in the outer disc. Inside the gas envelopes of protoplanets, enhanced settling may lead to a reduced dust opacity, which facilitates the contraction of the envelope. We show that the relevant physical set up can be recreated in a laboratory setting. This will allow our numerical calculations to be investigated experimentally in the future.

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organization
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Contribution to journal
publication status
published
subject
keywords
Hydrodynamics, Instabilities, Methods: numerical, Planets and satellites: formation, Protoplanetary disks, Turbulence
in
Astronomy and Astrophysics
volume
591
publisher
EDP Sciences
external identifiers
  • scopus:84977079536
  • wos:000379141300142
ISSN
0004-6361
DOI
10.1051/0004-6361/201526272
language
English
LU publication?
yes
id
c59cbbe8-fbcf-4f8c-99f5-f93c6ad795e8
date added to LUP
2017-01-17 16:40:25
date last changed
2017-11-12 04:28:10
@article{c59cbbe8-fbcf-4f8c-99f5-f93c6ad795e8,
  abstract     = {<p>The behaviour of sedimenting particles depends on the dust-to-gas ratio of the fluid. Linear stability analysis shows that solids settling in the Epstein drag regime would remain homogeneously distributed in non-rotating incompressible fluids, even when dust-to-gas ratios reach unity. However, the nonlinear evolution has not been probed before. Here, we present numerical calculations indicating that, in a particle-dense mixture, solids spontaneously mix out of the fluid and form swarms that are overdense in particles by at least a factor 10. The instability is caused by mass-loaded regions locally breaking the equilibrium background stratification. The driving mechanism depends on nonlinear perturbations of the background flow and shares some similarity to the streaming instability in accretion discs. The resulting particle-rich swarms may stimulate particle growth by coagulation. In the context of protoplanetary discs, the instability could be relevant for aiding small particles to settle to the midplane in the outer disc. Inside the gas envelopes of protoplanets, enhanced settling may lead to a reduced dust opacity, which facilitates the contraction of the envelope. We show that the relevant physical set up can be recreated in a laboratory setting. This will allow our numerical calculations to be investigated experimentally in the future.</p>},
  articleno    = {A133},
  author       = {Lambrechts, M. and Johansen, A. and Capelo, H. L. and Blum, J. and Bodenschatz, E.},
  issn         = {0004-6361},
  keyword      = {Hydrodynamics,Instabilities,Methods: numerical,Planets and satellites: formation,Protoplanetary disks,Turbulence},
  language     = {eng},
  month        = {07},
  publisher    = {EDP Sciences},
  series       = {Astronomy and Astrophysics},
  title        = {Spontaneous concentrations of solids through two-way drag forces between gas and sedimenting particles},
  url          = {http://dx.doi.org/10.1051/0004-6361/201526272},
  volume       = {591},
  year         = {2016},
}