Mini-Combust - an Open-Source Unstructured FGM Combustion Mini-app for Co-Designing Aero-Engines at Extreme Scale

We present Mini-Combust, a representative mini-application to explore algorithms of interest for simulating combustion in aero turbine engines. Mini-Combust uses an asynchronous coupled Lagrangian-Eulerian (particle and FVM flow field solver) approach and incorporates basic models for heat transfer, turbulence, boundary conditions, convection schemes, fuel, spray atomisation and emissions. The mini-app is developed in a modular and scalable setup with highly optimized code-paths for executing the solvers on multi-core CPU systems and on CPU/GPU heterogeneous systems. We investigate its performance and scalability on two high-performance computing systems, exploring key performance profiles on up to 32k CPU cores and 128 GPUs, solving a test case representative of a bluff-body swirl burner from industry. Results demonstrate the highly memory-bound nature of the key kernels of the solvers. We see a speedup of 8.8× on an H100 node compared to a power-equivalent number of CPU nodes when offloading the most time-consuming component, the Eulerian solver, to GPUs, executing the asynchronous solvers in a hybrid CPU-GPU manner on an NVIDIA H100 GPU node. Additionally, we see how the communication overhead between the two solvers becomes more pronounced at increasing scale. Mini-Combust is available as open-source software.