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Particle radial distribution function and relative velocity measurement in turbulence at small particle-pair separations.

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Title: Particle radial distribution function and relative velocity measurement in turbulence at small particle-pair separations.
Authors: Hammond, Adam1 (AUTHOR), Meng, Hui1 (AUTHOR) huimeng@buffalo.edu
Source: Journal of Fluid Mechanics. 8/25/2021, Vol. 921, p1-18. 18p.
Subjects: Relative velocity, Velocity measurements, Turbulence, Particle tracking velocimetry, Boltzmann's equation, Radial distribution function, Turbulent flow
Abstract: Particle collisions in turbulent flow are critical to particle agglomeration and droplet coalescence. The collision kernel can be evaluated by radial distribution function (RDF) and radial relative velocity (RV) between particles at small separations $r$. Previously, the smallest $r$ was limited to roughly the Kolmogorov length $\eta$ due to particle position uncertainty and image overlap. We report a new approach to measuring RDF and RV near contact ($r/a \approx 2.07$ , where $a$ is particle radius). Three-dimensional particle tracking velocimetry using the four-pulse shake-the-box algorithm recorded short tracks with the interpolated midpoints registered as particle positions, avoiding image overlap and track mismatch. We measured RDF and RV of inertial particles in a one metre diameter isotropic air turbulence chamber with Taylor Reynolds number $Re_\lambda =324$ , $a=12 - 16\ \mathrm {\mu }\textrm {m}$ $({\approx }0.12\eta)$ and Stokes number ${\approx }0.7$. At large $r$ the measured RV agrees with the literature, but when $r the first moment of negative RV starts to increase, reaching 10 times higher values than direct numerical simulations of non-interacting particles. Likewise, RDF scales as $r^{-0.39}$ when $r>\eta$ , reflecting the well-known scaling for polydisperse particles, but when $r\lessapprox \eta$ , RDF scales as $r^{-6}$ , yielding 1000 times higher near-contact RDF than simulations. Such RV enhancement and extreme clustering at small $r$ can be attributed to particle–particle interactions including hydrodynamic interactions, which are not well-understood. Uncertainty analysis substantiates the observed trends. This first-ever simultaneous RDF and RV measurement at small separations provides a clear glimpse into the clustering and relative velocities of particles in turbulence near-contact. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Fluid Mechanics is the property of Cambridge University Press and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
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Header DbId: egs
DbLabel: Engineering Source
An: 152316718
AccessLevel: 6
PubType: Academic Journal
PubTypeId: academicJournal
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Items – Name: Title
  Label: Title
  Group: Ti
  Data: Particle radial distribution function and relative velocity measurement in turbulence at small particle-pair separations.
– Name: Author
  Label: Authors
  Group: Au
  Data: <searchLink fieldCode="AR" term="%22Hammond%2C+Adam%22">Hammond, Adam</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Meng%2C+Hui%22">Meng, Hui</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> huimeng@buffalo.edu</i>
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Fluid+Mechanics%22">Journal of Fluid Mechanics</searchLink>. 8/25/2021, Vol. 921, p1-18. 18p.
– Name: Subject
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  Data: <searchLink fieldCode="DE" term="%22Relative+velocity%22">Relative velocity</searchLink><br /><searchLink fieldCode="DE" term="%22Velocity+measurements%22">Velocity measurements</searchLink><br /><searchLink fieldCode="DE" term="%22Turbulence%22">Turbulence</searchLink><br /><searchLink fieldCode="DE" term="%22Particle+tracking+velocimetry%22">Particle tracking velocimetry</searchLink><br /><searchLink fieldCode="DE" term="%22Boltzmann's+equation%22">Boltzmann's equation</searchLink><br /><searchLink fieldCode="DE" term="%22Radial+distribution+function%22">Radial distribution function</searchLink><br /><searchLink fieldCode="DE" term="%22Turbulent+flow%22">Turbulent flow</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Particle collisions in turbulent flow are critical to particle agglomeration and droplet coalescence. The collision kernel can be evaluated by radial distribution function (RDF) and radial relative velocity (RV) between particles at small separations $r$. Previously, the smallest $r$ was limited to roughly the Kolmogorov length $\eta$ due to particle position uncertainty and image overlap. We report a new approach to measuring RDF and RV near contact ($r/a \approx 2.07$ , where $a$ is particle radius). Three-dimensional particle tracking velocimetry using the four-pulse shake-the-box algorithm recorded short tracks with the interpolated midpoints registered as particle positions, avoiding image overlap and track mismatch. We measured RDF and RV of inertial particles in a one metre diameter isotropic air turbulence chamber with Taylor Reynolds number $Re_\lambda =324$ , $a=12 - 16\ \mathrm {\mu }\textrm {m}$ $({\approx }0.12\eta)$ and Stokes number ${\approx }0.7$. At large $r$ the measured RV agrees with the literature, but when $r the first moment of negative RV starts to increase, reaching 10 times higher values than direct numerical simulations of non-interacting particles. Likewise, RDF scales as $r^{-0.39}$ when $r>\eta$ , reflecting the well-known scaling for polydisperse particles, but when $r\lessapprox \eta$ , RDF scales as $r^{-6}$ , yielding 1000 times higher near-contact RDF than simulations. Such RV enhancement and extreme clustering at small $r$ can be attributed to particle–particle interactions including hydrodynamic interactions, which are not well-understood. Uncertainty analysis substantiates the observed trends. This first-ever simultaneous RDF and RV measurement at small separations provides a clear glimpse into the clustering and relative velocities of particles in turbulence near-contact. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Journal of Fluid Mechanics is the property of Cambridge University Press and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
  BibEntity:
    Identifiers:
      – Type: doi
        Value: 10.1017/jfm.2021.486
    Languages:
      – Code: eng
        Text: English
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      Pagination:
        PageCount: 18
        StartPage: 1
    Subjects:
      – SubjectFull: Relative velocity
        Type: general
      – SubjectFull: Velocity measurements
        Type: general
      – SubjectFull: Turbulence
        Type: general
      – SubjectFull: Particle tracking velocimetry
        Type: general
      – SubjectFull: Boltzmann's equation
        Type: general
      – SubjectFull: Radial distribution function
        Type: general
      – SubjectFull: Turbulent flow
        Type: general
    Titles:
      – TitleFull: Particle radial distribution function and relative velocity measurement in turbulence at small particle-pair separations.
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          Name:
            NameFull: Hammond, Adam
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          Name:
            NameFull: Meng, Hui
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            – D: 25
              M: 08
              Text: 8/25/2021
              Type: published
              Y: 2021
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              Value: 921
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            – TitleFull: Journal of Fluid Mechanics
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