@article{Bouckley:2026:10.1017/jfm.2026.12012,
author = {Bouckley, ER and Lewin, SF and Lefauve, A},
doi = {10.1017/jfm.2026.12012},
journal = {Journal of Fluid Mechanics},
title = {Early onset of secondary shear instability in Kelvin–Helmholtz braids at high Reynolds number},
url = {http://dx.doi.org/10.1017/jfm.2026.12012},
volume = {1043},
year = {2026}
}

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TY  - JOUR
AB  - <jats:p>                    We study the onset of two-dimensional secondary shear instability (SSI) in the braid regions connecting primary Kelvin–Helmholtz billows in stratified shear flows. While strain induced by the billows stabilises the braids, it also compresses their tilted isopycnals, enhancing baroclinic shear that enables rapid perturbation growth. By modifying the classical analysis of Corcos & Sherman (1976                    <jats:italic>J. Fluid Mech.</jats:italic>                    73, 241–264) in braid-aligned coordinates and adding an instability criterion based on the ratio of strain rate to shear, we develop an inviscid, time-dependent model for the braid evolution and the onset of SSI. We show that the criterion for instability can be achieved significantly earlier than the saturation of the primary billow at sufficiently high initial Richardson number                    <jats:inline-formula>                      <jats:alternatives>                        <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" content-type="simple" xlink:href="S0022112026120126_inline1.png">                          <jats:alt-text content-type="machine-generated">italic Ri</jats:alt-text>                        </jats:inline-graphic>                        <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cambridge.org/core/metadata" xmlns:core="http://cambridge.org/core" xmlns:c="http://cambridge.org/core/content">                          <mml:mrow>                            <mml:mtext mathvariant="italic" class="MJX-tex-mathit">Ri</mml:
AU  - Bouckley,ER
AU  - Lewin,SF
AU  - Lefauve,A
DO  - 10.1017/jfm.2026.12012
PY  - 2026///
SN  - 0022-1120
TI  - Early onset of secondary shear instability in Kelvin–Helmholtz braids at high Reynolds number
T2  - Journal of Fluid Mechanics
UR  - http://dx.doi.org/10.1017/jfm.2026.12012
UR  - https://doi.org/10.1017/jfm.2026.12012
VL  - 1043
ER  - 

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