Simulating Galaxy Formation with Fewer than a Trillion Zones

星系演化中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。由于星系和恒星在空间尺度上的巨大差异，用目前的计算技术仍然不可能直接模拟相关的物理过程；人们必须求助于亚网格模型来处理关键过程，如湍流。该项目的合作小组将采用Flash-3流体动力学程序来测试高雷诺数(低粘度)湍流的亚格子模型，以对抗实验室实验和直接的蛮力计算。然后，他们将把修改后的流体力学模型应用于三个天体物理问题：(1)活动星系核驱动的气泡在星系团中心的作用。模拟这些气泡将需要考虑浮力驱动的不稳定性，这些不稳定性的尺度太小，无法直接解决。(2)球状簇状重元素富集型。球状星团恒星在化学上是均匀的，一定是由混合良好的物质形成的。包括剪切驱动不稳定性的亚格子模型将允许对混合进行详细模拟，从而限制这些星系团形成的时间和地点。(3)星暴星系中超新星驱动的外流的发展。由于星际介质的冷却时间很短，这将需要对超音速湍流进行建模。S项目的更广泛影响包括研究生和博士后研究员培训、公开演讲、计算流体力学本科课程的开发以及向社区发布模拟包。

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.