Dept. of Scientific Computing,
Florida State University

"Physics, Modeling, and Large Scale Simulations of Turbulent Reactive Flows"

Feb 2, 2022 Schedule:

Tea Time - Virtual ( Zoom)

 

03:00 to 03:30 PM Eastern Time (US and Canada)

Colloquium - F2F ( 499 DSL) / Virtual ( Zoom)

 

03:30 to 04:30 PM Eastern Time (US and Canada)

Abstract:

We present the results of simulations of magnetized, reactive turbulence for conditions expected to exist in outer layers of massive white dwarfs during the advanced stages of the deflagration-driven explosion. In the present scenario an initially quiescent, low density plasma is perturbed by the approaching flame front, which drives turbulence on large scales due to Rayleigh-Taylor (RT) instability, and self-heated by nuclear burning.

We probe a parameter space of this problem by obtaining a series of models systematically varying characteristics of turbulence and initial strength of the magnetic field. The observed behavior is qualitatively similar to previously reported results of hydrodynamic simulations. Deflagration-to-detonation transition (DDT) is facilitated by the Zel'dovich reactivity gradient mechanism and occurs about 100 ms after the self-heating of plasma is enabled. Such relatively short detonation delay times are observed despite the fact that the turbulence is driven using relatively lower, realistic energies characteristic of the RT-driven supernova flame turbulence. The resulting turbulence Mach number is ~0.3.

We find the DDT delay time is a sensitive function of the turbulence compressibility with shorter delay times observed in models in which most of the driving energy injected on large scales is in solenoidal modes. Such perturbations are consistent with the RT-driven turbulence. For realistic initial magnetic field values(~10 MG or higher), the field is rapidly amplified with the average plasma beta reaching about 0.1 well before carbon ignites.

We discuss the magnetic field amplification mechanism, how the magnetic field participates in the process of preconditioning, and its role in accelerating DDT in the context of the Zel'dovich mechanism. Our results motivate observations aimed at measuring magnetic fields in Type Ia supernovae and future theoretical and computational studies of magnetized white dwarfs.