Development of a Stiffness Based Chemistry Load Balancing Scheme, and Optimization of Input/Output and Communication, to Enable Massively Parallel High Fidelity Internal Combustion Engine Simulations

Abstract

A closedcycle gasoline compression ignition (GCI) engine simulation near top dead center (TDC) was used to profile the performance of a parallel commercial engine computational fluid dynamics (CFD) code, as it was scaled on up to 4096 cores of an IBM Blue Gene/Q (BG/Q) supercomputer. The test case has 9 أ— 106 cells near TDC, with a fixed mesh size of 0.15 mm, and was run on configurations ranging from 128 to 4096 cores. Profiling was done for a small duration of 0.11 crank angle degrees near TDC during ignition. Optimization of input/output (I/O) performance resulted in a significant speedup in reading restart files, and in an over 100times speedup in writing restart files and files for postprocessing. Improvements to communication resulted in a 1400times speedup in the mesh load balancing operation during initialization, on 4096 cores. An improved, “stiffnessbasedâ€‌ algorithm for load balancing chemical kinetics calculations was developed, which results in an over threetimes faster runtime near ignition on 4096 cores relative to the original load balancing scheme. With this improvement to load balancing, the code achieves over 78% scaling efficiency on 2048 cores, and over 65% scaling efficiency on 4096 cores, relative to 256 cores.