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J Zhang, O.E.B. Messer, A.M. Khokhlov, T. Plewa (U of Chicago)
Simulations of Type Ia supernovae are characterized by vastly disparate spatial scales, spanning some 12 orders of magnitude. This large dynamic range cannot be captured in any modern direct numerical simulation. Therefore, a subgrid model is used to describe a number of unresolved physical processes taking place on the smallest scales. All modern Type Ia supernova simulations currently use steady-state subgrid models. In particular, velocity perturbations are assumed to stem from either a Kolmogorov cascade from larger scales (Reinecke et al. 2002) or are generated by local Rayleigh-Taylor instabilities (Khokhlov 1995). In all of these descriptions, the effective flame speed is assumed to be a function of the local instantaneous (steady-state) velocity field. Improvements to these types of subgrid models must include the possibility of contributions from non-steady velocity perturbations.
We have developed a set of diagnostic tools for the FLASH code designed to study the non-steady evolution of the flame front on scales on which the flame surface is directly affected by the local velocity field. The tools are designed to measure individually the flame surface creation and destruction terms. These terms describe the time evolution of a flame surface subject to Rayleigh-Taylor instabilities in periodic domains. In this work we study correlations between the non-steady flame propagation and characteristics of the velocity field. These results will provide the foundation for a non-steady subgrid flame evolution model. This model will be a key component of the next generation of large-scale supernova simulations.
We thank G. Weirs, N. Vladimirova, R. Rosner, D. Q. Lamb, and J. Truran for their contributions to this project.
References:
Khokhlov A.M. 1995, Apj, 449,695.
Reinecke, M., Hillebrandt, W. and Niemeyer, J. C, 2002, A&A, 386, 936.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.