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Subsonic Burning Fronts (aka Flames)

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Contact: F.X.Timmes
my one page vitae,
full vitae,
research statement, and
teaching statement.
Turbulent Chemical Diffusion In Convectively Bounded Carbon Flames (2016)
It has been proposed that mixing induced by convective overshoot can disrupt the inward propagation of carbon deflagrations in super-asymptotic giant branch stars. To test this theory, in this paper by Lacoanet et al we study an idealized model of convectively bounded carbon flames with 3D hydrodynamic simulations of the Boussinesq equations using the pseudospectral code Dedalus. Because the flame propagation timescale is is much longer than the convection timescale, we approximate the flame as fixed in space, and only consider its effects on the buoyancy of the fluid. By evolving a passive scalar field, we derive a turbulent chemical diffusivity produced by the convection as a function of height, Dt(z). Convection can stall a flame if the chemical mixing timescale, set by the turbulent chemical diffusivity, Dt, is shorter than the flame propagation timescale, set by the thermal diffusivity, κ, i.e., when $\Dt > \kappa$. However, we find Dt < κ for most of the flame because convective plumes are not dense enough to penetrate into the flame. Extrapolating to realistic stellar conditions, this implies that convective mixing cannot stall a carbon flame and that ``hybrid carbon-oxygen-neon'' white dwarfs are not a typical product of stellar evolution.

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Bouancy frequency
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2D vertical slices
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Dt versus height turbflame speeds


Propagation of Nuclear Flames IV (2007)
This paper explores how including the key neutron-rich isotope 22Ne changes the speed of laminar flames propagating through carbon-oxygen white dwarf.

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flame speeds
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Ye changes with 22Ne abundance


Propagation of Nuclear Flames III (2000)
How fast does a laminar flame from propagate through helium rich compositions? This paper explores some trends. I can't believe that I didn't publish the result that the final composition behind such flames is calcium, titanium, and chromium rich. Arrggh!

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laminar helium flame
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regimes in the rho-T plane
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heating & cooling


Propagation of Nuclear Flames II (1994)
How fast does a laminar flame from propagate into degenerate oxygen, magnesium, and neon Ye=0.5 compositions when bounded by a convective region? We explore answers in this paper.

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laminar ONeMg flame
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balanced power curves
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bounded flame speeds


Propagation of Nuclear Flames I (1992)
How fast does a laminar flame from propagate outward through degenerate carbon-oxygen and oxygen-neon-magnesium? We explore answers in this paper. These Ye=0.5 laminar flame speeds are used in many supernova type Ia models.

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laminar oxygen-neon flame
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carbon-oxygen flame speeds
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density recovery
 



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