Turbulence-Flame Interactions in Type Ia Supernovae

TL;DR

This paper uses high-resolution 3D simulations to study how turbulence affects nuclear flames in type Ia supernovae, revealing a transition from laminar to turbulent burning regimes at specific densities.

Contribution

It provides detailed simulation results on flame-turbulence interactions across different densities, highlighting the transition from laminar to turbulent regimes in supernova conditions.

Findings

Transition density between laminar and turbulent regimes is between 1 and 3 x 10^7 g/cm^3.

Turbulence broadens the flame, making it resemble a laminar flame with an effective diffusion coefficient.

At larger scales, the flame becomes complex and unsteady, affecting supernova explosion models.

Abstract

The large range of time and length scales involved in type Ia supernovae (SN Ia) requires the use of flame models. As a prelude to exploring various options for flame models, we consider, in this paper, high-resolution three-dimensional simulations of the small-scale dynamics of nuclear flames in the supernova environment in which the details of the flame structure are fully resolved. The range of densities examined, 1 to $8 \times 10^7$ g cm$^{-3}$, spans the transition from the laminar flamelet regime to the distributed burning regime where small scale turbulence disrupts the flame. The use of a low Mach number algorithm facilitates the accurate resolution of the thermal structure of the flame and the inviscid turbulent kinetic energy cascade, while implicitly incorporating kinetic energy dissipation at the grid-scale cutoff. For an assumed background of isotropic Kolmogorov turbulence with an energy characteristic of SN Ia, we find a transition density between 1 and $3 \times 10^7$ g cm$^{-3}$ where the nature of the burning changes qualitatively. By $1 \times 10^7$ g cm$^{-3}$, energy diffusion by conduction and radiation is exceeded, on the flame scale, by turbulent advection. As a result, the effective Lewis Number approaches unity. That is, the flame resembles a laminar flame, but is turbulently broadened with an effective diffusion coefficient, $D_T \sim u' l$, where $u'$ is the turbulent intensity and $l$ is the integral scale. For the larger integral scales characteristic of a real supernova, the flame structure is predicted to become complex and unsteady. Implications for a possible transition to detonation are discussed.