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Instability and breaking of internal waves in a horizontal shear layer.

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Title: Instability and breaking of internal waves in a horizontal shear layer.
Authors: Lewin, Sam F.1 (AUTHOR) samuel.lewin7108@gmail.com, Kaminski, Alexis K.1,2 (AUTHOR), Balakrishna, Arun2,3 (AUTHOR), Couchman, Miles M.P.1,3 (AUTHOR)
Source: Journal of Fluid Mechanics. 5/10/2026, Vol. 1034, p1-40. 40p.
Subjects: Internal waves, Shear flow, Numerical analysis, Energy transfer, Flow instability, Turbulence, Fluid dynamics
Abstract: The behaviour of internal waves propagating in a background shear flow is studied in the case where the direction of shear is orthogonal to gravity. Ray-tracing theory is used to predict properties of the wave state at locations where instability occurs. Local wave energy growth is found to result from two distinct mechanisms: an increase in wave steepness due to refraction by the shear or an increase in streamwise velocity perturbations due to wave advection of the background flow. Based on the initial conditions, a dimensionless perturbation energy ratio $F$ is constructed to predict the relative importance of these two mechanisms in facilitating wave breaking. When $F$ is small and waves become locally steep, perturbation kinetic and potential energy remain approximately equipartitioned and subsequent instabilities are expected to develop due to a combination of shear and convection. On the other hand, as $F$ increases, kinetic energy dominates and wave advection of momentum may instead cause breaking to become increasingly driven by enhanced vertical shear. To test these predictions, fully nonlinear direct numerical simulations are conducted, spanning a range of wave-breaking dynamics. Good qualitative agreement with the theory is found despite substantial departures from the underlying assumptions. Wave breaking leads to significant turbulent dissipation, which in some cases greatly exceeds the initial wave energy. Momentum and energy transfers between the wave, background flow and turbulence are found to be sensitive to the dynamics of breaking, as are the mixing properties. [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: 193952145
AccessLevel: 6
PubType: Academic Journal
PubTypeId: academicJournal
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  Data: Instability and breaking of internal waves in a horizontal shear layer.
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  Data: <searchLink fieldCode="AR" term="%22Lewin%2C+Sam+F%2E%22">Lewin, Sam F.</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> samuel.lewin7108@gmail.com</i><br /><searchLink fieldCode="AR" term="%22Kaminski%2C+Alexis+K%2E%22">Kaminski, Alexis K.</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Balakrishna%2C+Arun%22">Balakrishna, Arun</searchLink><relatesTo>2,3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Couchman%2C+Miles+M%2EP%2E%22">Couchman, Miles M.P.</searchLink><relatesTo>1,3</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Fluid+Mechanics%22">Journal of Fluid Mechanics</searchLink>. 5/10/2026, Vol. 1034, p1-40. 40p.
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  Data: <searchLink fieldCode="DE" term="%22Internal+waves%22">Internal waves</searchLink><br /><searchLink fieldCode="DE" term="%22Shear+flow%22">Shear flow</searchLink><br /><searchLink fieldCode="DE" term="%22Numerical+analysis%22">Numerical analysis</searchLink><br /><searchLink fieldCode="DE" term="%22Energy+transfer%22">Energy transfer</searchLink><br /><searchLink fieldCode="DE" term="%22Flow+instability%22">Flow instability</searchLink><br /><searchLink fieldCode="DE" term="%22Turbulence%22">Turbulence</searchLink><br /><searchLink fieldCode="DE" term="%22Fluid+dynamics%22">Fluid dynamics</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: The behaviour of internal waves propagating in a background shear flow is studied in the case where the direction of shear is orthogonal to gravity. Ray-tracing theory is used to predict properties of the wave state at locations where instability occurs. Local wave energy growth is found to result from two distinct mechanisms: an increase in wave steepness due to refraction by the shear or an increase in streamwise velocity perturbations due to wave advection of the background flow. Based on the initial conditions, a dimensionless perturbation energy ratio $F$ is constructed to predict the relative importance of these two mechanisms in facilitating wave breaking. When $F$ is small and waves become locally steep, perturbation kinetic and potential energy remain approximately equipartitioned and subsequent instabilities are expected to develop due to a combination of shear and convection. On the other hand, as $F$ increases, kinetic energy dominates and wave advection of momentum may instead cause breaking to become increasingly driven by enhanced vertical shear. To test these predictions, fully nonlinear direct numerical simulations are conducted, spanning a range of wave-breaking dynamics. Good qualitative agreement with the theory is found despite substantial departures from the underlying assumptions. Wave breaking leads to significant turbulent dissipation, which in some cases greatly exceeds the initial wave energy. Momentum and energy transfers between the wave, background flow and turbulence are found to be sensitive to the dynamics of breaking, as are the mixing properties. [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.2026.11456
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 40
        StartPage: 1
    Subjects:
      – SubjectFull: Internal waves
        Type: general
      – SubjectFull: Shear flow
        Type: general
      – SubjectFull: Numerical analysis
        Type: general
      – SubjectFull: Energy transfer
        Type: general
      – SubjectFull: Flow instability
        Type: general
      – SubjectFull: Turbulence
        Type: general
      – SubjectFull: Fluid dynamics
        Type: general
    Titles:
      – TitleFull: Instability and breaking of internal waves in a horizontal shear layer.
        Type: main
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            NameFull: Lewin, Sam F.
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            NameFull: Kaminski, Alexis K.
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            NameFull: Balakrishna, Arun
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            NameFull: Couchman, Miles M.P.
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            – D: 10
              M: 05
              Text: 5/10/2026
              Type: published
              Y: 2026
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              Value: 1034
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