A Multigroup Method for Radiation with Scattering in Three-Dimensional Hydrodynamic Simulations
A Multigroup Method for Radiation with Scattering in Three-Dimensional Hydrodynamic Simulations
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DOI：
10.1086/308934
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发表时间：
2000-06
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影响因子：
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通讯作者：
R. Skartlien
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文献类型：
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作者：
R. Skartlien
在三维模拟中，为了避免极大的计算成本，在放射治疗中仍然需要大量的近似。三维太阳辐射流体动力学模拟以前假设局部热力学平衡（LTE），这一假设在深光球中很好地工作。这项工作旨在通过包括散射辐射使这些模拟更进一步，目标是在三维中建模色球。我们允许相干各向同性散射，这改变了色球的热结构和波的振幅。群平均不透明度系数用于群平均源函数，其中包含近似散射项和热发射率的精确贡献。由此产生的三维散射问题允许一个新的迭代方法的计算效率的解决方案。我们比较了准确的波长积分单色的解决方案与相应的近似解决方案的太阳条件。我们发现，从组得到的总通量发散偏差小于10%的精确解。当使用这些组而不是完整的单色解决方案时，在太阳条件的测试情况下，CPU时间减少了约100倍。
Substantial approximations in the treatment of radiation are still necessary in three-dimensional simulations in order to avoid extremely large computational costs. Solar radiation hydrodynamic simulations in three dimensions have previously assumed local thermodynamic equilibrium (LTE); an assumption that works well in the deep photosphere. This work aims at bringing these simulations a step further by including scattered radiation, with the goal of modeling chromospheres in three dimensions. We allow for coherent isotropic scattering, which alters the thermal structure and wave amplitudes in the chromosphere. Group mean opacity coefficients are used in group mean source functions that contain approximate scattering terms and exact contributions from thermal emissivity. The resulting three-dimensional scattering problem allows for a computationally efficient solution by a new iteration method. We have compared exact wavelength-integrated monochromatic solutions with the corresponding approximate solutions for solar conditions. We find that the total flux divergence obtained from the groups deviates less than 10% from the exact solution. When using these groups rather than the full monochromatic solution, the CPU time is reduced by a factor of about 100 in a test case for solar conditions.