热双稳态气体中受迫turbulence的参数研究
Forced turbulence in thermally bistable gas: A parameter study
摘要：
内容：热不稳定性是扩散星际介质中湍流的动力学因子之一，其中湍流和热不稳定性以高度非线性的方式相互作用。目的：研究不同模拟参数下热双稳态气体湍流的基本特性。由此产生的冷气体分数可以作为银河系尺度模拟的参数化。方法：在周期性的盒子中通过压缩随机强迫在大尺度上诱导湍流。在均匀网格上求解了具有恒定UV加热和参数化冷却函数的可压缩Euler方程。我们调查了几个值的平均密度的气体和不同大小的强迫。与其他数值研究相比，螺线管强迫也被应用。结果：经过一个瞬态阶段，我们观察到一个统计稳定的湍流状态接近。压缩强迫通常产生两相介质，其中冷气体的分数减少以增加强迫强度。这种现象可以用湍流混合来解释。我们还发现指数的气体密度的概率密度函数的幂律尾部。螺线管强迫，另一方面，似乎防止演变成两相介质的某些参数区域。结论：热双稳态湍流动力学对初始状态和强迫特性具有很强的敏感性。
英文摘要：
Context: The thermal instability is one of the dynamical agents for turbulence in the diffuse interstellar medium, where both, turbulence and thermal instability interact in a highly non-linear manner. Aims: We study basic properties of turbulence in thermally bistable gas for variable simulation parameters. The resulting cold gas fractions can be applied as parameterisation in simulations on galactic scales. Methods: Turbulent flow is induced on large scales by means of compressive stochastic forcing in a periodic box. The compressible Euler equations with constant UV heating and a parameterised cooling function are solved on uniform grids. We investigate several values of the mean density of the gas and different magnitudes of the forcing. For comparison with other numerical studies, solenoidal forcing is applied as well. Results: After a transient phase, we observe that a state of statistically stationary turbulence is approached. Compressive forcing generally produces a two-phase medium, with a decreasing fraction of cold gas for increasing forcing strength. This behaviour can be explained on the basis of turbulent mixing. We also find indications for power-law tails of probability density functions of the gas density. Solenoidal forcing, on the other hand, appears to prevent the evolution into a two-phase-medium for certain parameter regions. Conclusions: The dynamics of thermally bistable turbulence shows a substantial sensitivity on the initial state and the forcing properties.
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