The interaction between shear and fingering (thermohaline) convection. (arXiv:1905.07636v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Garaud_P/0/1/0/all/0/1">P. Garaud</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kumar_A/0/1/0/all/0/1">A. Kumar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sridhar_J/0/1/0/all/0/1">J. Sridhar</a>
Fingering convection is a turbulent mixing process that can occur in stellar
radiative regions whenever the mean molecular weight increases with radius. In
some cases, it can have a significant observable impact on stellar structure
and evolution. The efficiency of mixing by fingering convection as a standalone
process has been studied by Brown et al. (2013), but other processes such as
rotation, magnetic fields and shear can affect it. In this paper, we present a
first study of the effect of shear on fingering (thermohaline) convection in
astrophysics. Using Direct Numerical Simulations we find that a moderate amount
of shear (that is not intrinsically shear-unstable) always decreases the mixing
efficiency of fingering convection, as a result of the tilt it imparts to the
fingering structures. We propose a simple analytical extension of the Brown et
al. (2013) model in the presence of shear that satisfactorily explains the
numerically-derived turbulent compositional mixing coefficient for moderate
shearing rates, and can trivially be implemented in stellar evolution codes. We
also measure from the numerical simulations a turbulent viscosity, and find
that the latter is strongly tied to the turbulent compositional mixing
coefficient. Observational implications and caveats of the model are discussed.
Fingering convection is a turbulent mixing process that can occur in stellar
radiative regions whenever the mean molecular weight increases with radius. In
some cases, it can have a significant observable impact on stellar structure
and evolution. The efficiency of mixing by fingering convection as a standalone
process has been studied by Brown et al. (2013), but other processes such as
rotation, magnetic fields and shear can affect it. In this paper, we present a
first study of the effect of shear on fingering (thermohaline) convection in
astrophysics. Using Direct Numerical Simulations we find that a moderate amount
of shear (that is not intrinsically shear-unstable) always decreases the mixing
efficiency of fingering convection, as a result of the tilt it imparts to the
fingering structures. We propose a simple analytical extension of the Brown et
al. (2013) model in the presence of shear that satisfactorily explains the
numerically-derived turbulent compositional mixing coefficient for moderate
shearing rates, and can trivially be implemented in stellar evolution codes. We
also measure from the numerical simulations a turbulent viscosity, and find
that the latter is strongly tied to the turbulent compositional mixing
coefficient. Observational implications and caveats of the model are discussed.
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