Towards Understanding Some Astrophysical Flows using Multiscale Simulations with the FLASH Code

Many astrophysical systems have important behaviors on scales so disparate that even modern techniques such as adaptive mesh refinement cannot possibly resolve all of the dynamics. However, there are situations where the interactions between the scales are relatively simple; in these cases the system can be meaningfully decomposed into different sub-problems, which can be separately understood and then integrated back together into a large-scale model. Here we describe an in-progress computational astrophysics research program where such an approach is taken for two different problems - that of turbulent mixing in a large-scale flow between a high-speed hot wind and a cold, dense accretion disk; and turbulent ignition in what will become a Type Ia supernovae. In the case of the disk-wind interaction, the turbulent mixing is understood through parameter studies of small-scale mixing flows, with the aim of putting the resulting transport terms into a large-scale wind-disk model. In the case of ignition, the turbulence is itself the large-scale flow, and the ignition physics is the small-scale model which must be understood and inserted parametrically into the large-scale model. In both cases, the detailed modeling of the large number of small-scale models can easily exceed the later cost of the large-scale global computations.