Simulating Galaxy Formation with Fewer than a Trillion Zones

星系演化的关键问题集中在反馈过程——来自恒星和活动星系核（AGN）的能量和动量的注入。由于星系和恒星之间的空间尺度存在巨大差异，目前的计算技术仍然无法直接模拟相关的物理现象；对于湍流等关键过程，必须借助于子网格模型。该项目的合作团队将采用FLASH-3流体力学代码来测试高雷诺数（低粘度）湍流的子网格模型，以对抗实验室实验和直接的蛮力计算。然后，他们将把修正后的流体动力学模型应用于三个天体物理问题：(1)由星系团中心活动星系核提供动力的气泡的作用。模拟这些气泡需要在太小而无法直接解决的尺度上包括浮力驱动的不稳定性。(2)球状星团重元素富集。球状星团的恒星在化学上是均匀的，一定是由混合良好的物质形成的。包含剪切驱动不稳定性的子网格模型将允许详细模拟混合，从而约束这些团簇形成的时间和地点。(3)星爆星系中超新星驱动外流的发展。由于星际介质中的冷却时间短，这将需要超音速湍流的建模。这个项目吗?更广泛的影响包括研究生和博士后研究人员的培训，公开讲座的介绍，计算流体动力学本科课程的发展，以及向社区发布模拟软件包。

Critical questions in galaxy evolution center on the processes of feedback -- the injection of energy and momentum from stars and active galactic nuclei (AGN). Due to the vast difference in spatial scales between galaxies and stars, direct simulation of the relevant physics is still impossible with current computing technology; one must resort to subgrid models for key processes such as turbulence. The collaborating team on this project will adapt the FLASH-3 hydrodynamics code to test subgrid models of high Reynolds-number (low viscosity) turbulence against laboratory experiments and direct, brute-force calculations. They will then apply the modified hydrodynamic model to three astrophysical problems: (1) The role of bubbles powered by active galactic nuclei in the centers of galaxy clusters. Simulating these bubbles will require including buoyancy-driven instabilities on scales too small to be resolved directly. (2) Globular cluster heavy-element enrichment. Globular cluster stars are chemically homogeneous and must have formed from well-mixed material. Subgrid models that include shear-driven instabilities will allow detailed simulations of mixing that can constrain when and where these clusters were formed. (3) Development of supernova-driven outflows in starburst galaxies. Due to the short cooling times in the interstellar medium, this will require the modeling of supersonic turbulence. The project?s broader impact includes graduate student and postdoctoral researcher training, the presentation of public lectures, the development of an undergraduate course in computational fluid dynamics, and the release of simulation packages to the community.