Numerical Simulation of complex turbulent Flows with Discontinuous Galerkin Method

We present a performance analysis of the numerical code DG-comp which is based on a Local Discontinuous Galerkin method and designed for the simulation of compressible turbulent flows in complex geometries. In the code several subgrid-scale models for Large Eddy Simulation and a hybrid RANS-LES model are implemented. Within a PRACE Preparatory Access Project, the attention was mainly focused on the following aspects:
1. Testing of the parallel scalability on three different Tier-0 architectures available in PRACE (Fermi, MareNostrum3 and Hornet);
2. Parallel profiling of the application with the Scalasca tool;
3. Optimization of the I/O strategy with the HDF5 library.
Without any code optimizations it was found that the application demonstrated strong parallel scaling of more than 1000 cores on Hornet and MareNostrum, and least up to 16384 cores on Fermi. The performance characteristics giving rise to this behaviour were confirmed with Scalasca. As regards the I/O strategy, a modification to the code was made to allow the use of HDF5-formatted files for output. This enhancement resulted in an increase in performance for most input datasets and a significant decrease in the storage space required. Other data were collected on the influence of the optimal compiler options to employ on the different computer systems and the influence of numerical libraries for the linear algebra computations in the code.