High Performance LES on Earth Simulator: A Challenge for Vehicle Aerodynamics

Large Eddy Simulation (LES) of flow around the aerodynamic model ASMO was performed on the world-class, vector-processing parallel computing system "Earth Simulator." The software "FrontFlow/red" based on the unstructured Finite Volume Method was utilized in this study. The computational code was intensively optimized on Earth Simulator and high vectorization and parallelization of more than 95% and 99% respectively were achieved in the simulations on 256 parallel processors, which made it possible to complete the large-scale computations (25 million meshes with 150 GB memory) including the calculation of turbulence statistics in only two or three days. The obtained turbulence statistics such as the averaged pressure distribution on the vehicle body surface showed good agreement with existing wind-tunnel experimental data. Reynolds-Averaged Navier-Stokes simulation (RANS) using the standard k-ε model with the same grid resolutions as those of LES was also conducted, and the validity of LES against RANS was discussed in the context of its accuracy and the CPU time consumed. The most notable feature obtained in LES was the reproduction of the base pressure of the vehicle body, which, in contrast, RANS results poorly estimated. The wake structures were analyzed both in terms of averaged and instantaneous flow fields. As a result, it was shown that LES could be a dominant and effective turbulence model in the very near future for the computations of the flow around the vehicle with complex configurations.