Lead Name - Dean Townsley
Institutions - DOE NNSA/ASC Flash Center at the University of Chicago and Argonne
National Laboratory ALCF (project supported under the 2008 INCITE award program)
Contributors (in alphabetical order) - Ray Bair, Anshu Dubey Robert Fisher, Nathan
Hearn, Don Lamb, Katherine Riley
Title - Buoyancy-Driven Turbulent Nuclear Combustion
Abstract :
A fundamental challenge in our understanding of reactive flows is the process by which
turbulence wrinkles a combustive flame front, thereby increasing its surface area and
effective flame speed. In particular, the mechanism of buoyancy-driven turbulent
combustion is central to our understanding of the explosion mechanism of Type Ia
supernovae, which in turn play a key role in our understanding of the expansion of the
universe and the nature of dark energy.
We will present a visualization which demonstrates that turbulence develops behind the
surface of the flame, but the flame surface itself is effectively ``polished" by the action of
the flame, and is smooth beneath a certain critical scale. In addition, the turbulence
behind the flame front is inhomogeneous and non-steady, in contrast to the assumptions
made by many theoretical models of turbulent burning. This visualization clearly
demonstrates this complex result, which has significant ramifications for the modeling of
turbulence nuclear flames in Type Ia supernovae.
Caption:
These four frames represent three different ways of visualizing the same snapshot of a
simulation of buoyancy-driven turbulent reactive flow; each is complementary to the rest
and distinctively insightful. In this 3-D simulation, an initially planar flame surface
perturbed with a multimode perturbation burns its way upward through a stratified
medium under conditions characteristic of the nuclear-degenerate material at the central
density of a near-Chandrasekhar mass C/O white dwarf. Gravity is directed downward.
The leftmost frame visualizes the flame surface itself. The simulation tracks the surface
of the flame through the evolution of a scalar advection diffusion reaction equation; this
frame depicts an isocontour of this scalar at the flame surface. The next two frames to the
right present volume renderings of the velocity field, and the enstrophy. Here the
baroclinic mechanism leads to the generation of vorticity at the flame surface. The
magnitude of the turbulent velocities drop off behind the flame front over an integral
length scale. The rightmost frame shows the progression of the flame through the
computational domain.