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A. C. Calder (U. Chicago), R. G. Eastman (LLNL)
Incorporation of radiation transport into an Eulerian, general purpose astrophysical simulation code--one that uses a higher order Godunov scheme such as PPM for computing fluxes--is a challenging problem. The challenge lies in devising a scheme that remains accurate for all the extremes of physical conditions which might exist in an object where radiation dominates the dynamics, and where photon mean free paths might range from very short to infinite. Solution of the multi-D hydrodynamics equations is usually performed explicitly. Modern methods employ high accuracy advection schemes, with features built in to capture shocks and sharpen contact discontinuities. The radiation transport must be computed implicitly, which necessarily entails much lower accuracy. To address these difficulties, we have developed a new technique for coupling implicit radiation transport and explicit hydrodynamics that retains the high accuracy of the explicit advection scheme in regions of high optical depth, while at the same time allowing the radiation and gas to decouple in regions where the photon mean free path is long compared to the zone size. We are implementing this in the University of Chicago ASCI Center FLASH code as two temperature flux-limited diffusion. We will describe the method we have developed and give examples.
This work was supported by the U.S Department of Energy under grant No. B341495 to the Center for Astrophysical Thermonuclear Flashes at the University of Chicago and at LLNL by grant W-7405-ENG-48.
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