The Numerical Simulation of Radiative Shocks. II. Thermal Instabilities in Two-dimensional Models
The Numerical Simulation of Radiative Shocks. II. Thermal Instabilities in Two-dimensional Models
复制标题
辐射冲击的数值模拟。
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
M. Dopita
中科院分区：
文献类型：
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作者：
R. Sutherland;G. Bicknell;M. Dopita
我们展示了稳定和超稳定辐射冲击的高分辨率流体动力学模拟结果。结合幂律和现实天体物理冷却函数的一维分辨率研究，在冲击区的空间结构和过稳定振荡的频率方面都与解析解非常吻合。这是建立在 Strickland 和 Blondin 之前的工作基础上的，评估了我们代码的准确性并估计了构建可靠的星际辐射冲击多维模型所需的分辨率。这些模型表明，在多维流体动力学模拟中对冷却过程引起的时空结构进行精确建模需要高分辨率。然后，我们提出了具有不同输入密度涨落谱的非均匀二维模型，并表明所产生的震后密度和速度结构在很大程度上独立于初始种子涨落谱，并且小的波动可以导致在单个冷却时间尺度内完全形成二维的致密丝状结构。这些不均匀的二维结构由分形维数描述，分形维数在这些二维模拟中具有特征值。与均匀一维和二维模型相比，冷却非均匀冲击由于其分形结构而提高了冷却效率。辐射效率的增加伴随着动能到热能转换的减少，因为二维模型中额外的自由度允许动能重新定向到其他方向，从而产生二维湍流。
We present the results of high-resolution hydrodynamic simulations of stable and overstable radiative shocks. A one-dimensional resolution study, incorporating both power-law and realistic astrophysical cooling functions, agrees well with analytical solutions both in the spatial structure of the shocked zone and in the frequencies of overstable oscillations. This builds upon previous work by Strickland & Blondin, evaluating the accuracy of our code and estimating the resolution required to construct credible multidimensional models of interstellar radiative shocks. These models show that accurate modeling of the spatial and temporal structure induced by cooling processes in a multidimensional hydrodynamic simulation requires high resolution. We then present inhomogeneous two-dimensional models with varying input density fluctuation spectra and show that the resulting postshock density and velocity structures are largely independent of the initial seed fluctuation spectrum and that small fluctuations can result in a dense filamentary structure in two dimensions being fully developed in a single cooling timescale. These inhomogeneous two-dimensional structures are described by a fractal dimension, which takes a characteristic value in these two-dimensional simulations. Cooling inhomogeneous shocks have enhanced cooling efficiency, due to their fractal structure, compared to homogeneous one- and two-dimensional models. The increased radiative efficiency is accompanied by a decrease in the conversion of kinetic to thermal energy as the additional degrees of freedom in the two-dimensional models allow kinetic energy to be redirected in other directions, resulting in two-dimensional turbulence.