Title of Submission:
Simulation of Buoyancy-Driven Turbulent Nuclear Burning for a Froude Number of 0.010
Names of Contributors (Imagery, Science):
Imagery: Brad Gallagher, Flash Viz Group, Science: Dean Townslwey, Ray Bair, Robert Fisher, Nathan Hearn, Don Lamb, Katherine Riley
Teragird resources used:
UC/ANL teragrid used to render the animation, and was also used to compute vorticity components and magnitude from the velocity field data. This amounted to generating around 4 additional terabytes of derived data from two different datasets.
Imapact statement on how imagery contributes to the science:
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.
These four frames represent three different ways of visualizaing 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 near the central density of a Chandrasekhar mass 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 square of the curl of the velocity field. 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, corresponding with smaller and smaller scale vorticity structures where the turbulence is dissipated. The rightmost frame shows the progression of the flame through the computational domain.
Taken together, these visualizations demonstrate 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. These visualizations
clearly demonstrate this complex result, which has significant ramifications for the modeling of turbulence nuclear flames in Type Ia supernovae.
Click image for 1280x1024 version.
