A localised subgrid scale model for fluid dynamical simulations in astrophysics

Free access article

Issue		A&A Volume 450, Number 1, April IV 2006


Page(s)		283 - 294
Section		Stellar structure and evolution
DOI		http://dx.doi.org/10.1051/0004-6361:20053618

A&A 450, 283-294 (2006)
DOI: 10.1051/0004-6361:20053618

II. Application to type Ia supernovae

W. Schmidt^{1, 2}, J. C. Niemeyer¹, W. Hillebrandt² and F. K. Röpke²

¹ Lehrstuhl für Astronomie, Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
² Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany

(Received 11 June 2005 / Accepted 19 December 2005)

Abstract
The dynamics of the explosive burning process is highly sensitive to the flame speed model in numerical simulations of type Ia supernovae. Based upon the hypothesis that the effective flame speed is determined by the unresolved turbulent velocity fluctuations, we employ a new subgrid scale model which includes a localised treatment of the energy transfer through the turbulence cascade in combination with semi-statistical closures for the dissipation and non-local transport of turbulence energy. In addition, subgrid scale buoyancy effects are included. In the limit of negligible energy transfer and transport, the dynamical model reduces to the Sharp-Wheeler relation. According to our findings, the Sharp-Wheeler relation is insuffcient to account for the complicated turbulent dynamics of flames in thermonuclear supernovae. The application of a co-moving grid technique enables us to achieve very high spatial resolution in the burning region. Turbulence is produced mostly at the flame surface and in the interior ash regions. Consequently, there is a pronounced anisotropy in the vicinity of the flame fronts. The localised subgrid scale model predicts significantly enhanced energy generation and less unburnt carbon and oxygen at low velocities compared to earlier simulations.

Key words: stars: supernovae: general -- hydrodynamics -- turbulence -- convection -- methods: numerical

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