MFC 5.0: An exascale many-physics flow solver

Many problems of interest in engineering, medicine, and the fundamental sciences rely on high-fidelity flow simulation, making performant computational fluid dynamics solvers a mainstay of the open-source software community. Previous work MFC 3.0 was made a published, documented, and open-source solver via Bryngelson et al. Comp. Phys. Comm. (2021) with numerous physical features, numerical methods, and scalable infrastructure. MFC 5.0 is a significant update to MFC 3.0, featuring a broad set of well-established and novel physical models and numerical methods, as well as the introduction of GPU and APU (or superchip) acceleration. We exhibit state-of-the-art performance and ideal scaling on the first two exascale supercomputers, OLCF Frontier and LLNL El Capitan. Combined with MFC’s single-accelerator performance, MFC achieves exascale computation in practice, and achieved the largest-to-date public CFD simulation at 200 trillion grid points as a 2025 ACM Gordon Bell Prize finalist. New physical features include the immersed boundary method, N-fluid phase change, Euler–Euler and Euler–Lagrange sub-grid bubble models, fluid-structure interaction, hypo- and hyper-elastic materials, chemically reacting flow, two-material surface tension, magnetohydrodynamics (MHD), and more. Numerical techniques now represent the current state-of-the-art, including general relaxation characteristic boundary conditions, WENO variants, Strang splitting for stiff sub-grid flow features, and low Mach number treatments. Weak scaling to tens of thousands of GPUs on OLCF Summit and Frontier and LLNL El Capitan achieves efficiencies within 5% of ideal to over 90% of their respective system sizes. Strong scaling results for a 16-times increase in device count show parallel efficiencies over 90% on OLCF Frontier. MFC’s software stack has undergone further improvements, including continuous integration, which ensures code resilience and correctness through over 300 regression tests; metaprogramming, which reduces code length while maintaining performance portability; and code generation for computing chemical reactions.

工程、医学与基础科学领域的诸多核心问题均依赖高保真流动模拟，这使得高性能计算流体动力学（Computational Fluid Dynamics，CFD）求解器成为开源软件社区的支柱性工具。此前推出的MFC 3.0是由Bryngelson等人于《Computer Physics Communications》(2021)发表、附带完整文档的开源求解器，集成了多种物理模型、数值方法与可扩展基础设施。MFC 5.0是MFC 3.0的重大升级版本，搭载了大量成熟与新兴的物理模型及数值方法，同时新增了图形处理器（Graphics Processing Unit，GPU）与加速处理器（Accelerated Processing Unit，APU，或称超级芯片）加速功能。本求解器在首批两台百亿亿次超级计算机——橡树岭领先计算设施（Oak Ridge Leadership Computing Facility，OLCF）前沿（Frontier）与劳伦斯利弗莫尔国家实验室（Lawrence Livermore National Laboratory，LLNL）埃尔卡皮坦（El Capitan）上，展现出了顶尖性能与理想缩放特性。结合MFC的单加速器性能，该求解器可实现实际百亿亿次计算，并作为2025年ACM戈登贝尔奖（ACM Gordon Bell Prize）入围作品，完成了截至目前规模最大的公开CFD模拟，其网格点数达200万亿。新增物理特性包括浸入边界法、N流体相变模型、欧拉-欧拉与欧拉-拉格朗日亚网格气泡模型、流固耦合、亚弹性与超弹性材料、化学反应流、双材料表面张力以及磁流体动力学（Magnetohydrodynamics，MHD）等。当前采用的数值技术已达到业界顶尖水平，涵盖通用松弛特征边界条件、加权本质无振荡（Weighted Essentially Non-Oscillatory，WENO）格式变体、针对刚性亚网格流动特征的Strang分裂法以及低马赫数处理方案。在OLCF Summit、Frontier以及LLNL El Capitan上开展的数万GPU弱缩放测试显示，其并行效率与理想效率的偏差在5%以内，最高可达对应系统规模的90%以上。针对OLCF Frontier的强缩放测试结果表明，当设备数量提升16倍时，并行效率仍超过90%。MFC的软件栈也得到了进一步优化：包括通过超过300个回归测试保障代码鲁棒性与正确性的持续集成功能、在保持性能可移植性的同时缩减代码体量的元编程技术，以及用于化学反应计算的代码生成工具。