MOGLI：基于多流体流体动力学的多相气体模型
MOGLI: Model for Multiphase Gas using Multifluid hydrodynamics
AI总结：
针对多相气体模拟中冷气体结构尺寸与系统演化尺度差异大的挑战，提出亚网格框架MOGLI，通过两种局部湍流速度估计方法及三类相互作用建模，经多参数验证，可高效模拟多相气体并重现冷气体存活等特性。
摘要：
多相气体包含热气体（约10^6K）和冷气体（约10^4K），在各种尺度的天体物理介质中普遍存在。然而，由于冷气体结构的尺寸与这类气体影响相关系统演化的尺度之间存在巨大差异，模拟多相气体一直是一项长期挑战。在本研究中，我们为这种多相气体引入了一个新的亚网格框架MOGLI：基于多流体流体动力学的多相气体模型，该框架应用于多流体AREPO。我们基于基本原理和先前高分辨率小尺度模拟研究的理论结果开发了这种方法，使公式中的自由参数数量降至最低。我们将模型中的相互作用分为三个来源：阻力、湍流混合和冷气体增长。作为模型的一部分，我们还包括两种估计局部湍流速度的方法，一种使用Kolmogorov标度，另一种使用局部速度梯度。我们通过在不同模拟参数下与基准单流体模拟进行广泛比较，验证了该框架的不同组件，这些参数包括冷气体初始分辨率、湍流马赫数、空间分辨率和湍流的随机初始化。我们测试了完整方案和简化版本（包含和不包含冷气体增长）。我们发现，对于两种局部湍流速度估计方法，在不同模拟参数和诊断中都存在非常好的定性和定量一致性。我们还重现了冷气体存活标准等行为作为涌现特性。我们讨论了MOGLI的应用和可能的扩展，并通过运行一个计算上难以用高分辨率单流体模拟实现的模拟，展示了其能力。
英文摘要：
Multiphase gas, with hot ($\sim10^6$K) and cold ($\sim10^4$K) gas, is ubiquitous in astrophysical media across a wide range of scales. However, simulating multiphase gas has been a long-standing challenge, due to the large separation between the size of cold gas structures and the scales at which such gas impacts the evolution of associated systems. In this study, we introduce a new subgrid framework for such multiphase gas, MOGLI: Model for Multiphase Gas using Multifluid hydrodynamics, in multifluid AREPO. We develop this approach based on first principles and theoretical results from previous studies with resolved small-scale simulations, leading to a minimal number of free parameters in the formulation. We divide the interactions in the model into three sources: drag, turbulent mixing and cold gas growth. As part of the model, we also include two methods for estimating the local turbulent velocities, one using the Kolmogorov scaling, and the other using the local velocity gradients. We verify the different components of the framework through extensive comparison with benchmark single-fluid simulations across different simulation parameters, such as how resolved the cold gas is initially, the turbulent Mach number, spatial resolution, and random initialisation of turbulence. We test the complete scheme and a reduced version, with and without cold gas growth. We find a very good qualitative and quantitative agreement across the different simulation parameters and diagnostics for both local turbulent velocity estimation methods. We also reproduce behaviour like the cold gas survival criteria as an emergent property. We discuss the applications and possible extensions of MOGLI and demonstrate its capability by running a simulation which would be computationally prohibitive to run as a resolved single-fluid simulation.
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