|Boundary conditions for Nek5000
Nek5000 is written in mixed Fortran77/C and designed to employ fully larger-scale parallelism. The code has a long history of HPC development. Recently the larger-scale simulations were successful performed on the Cray XE6 system at PDC, KTH with 32,768 cores (“Coherent structures and dominant frequencies in a turbulent three-dimensional diffuser” by J. Malm, P. Schlatter and D. S. Henningson, accepted by JFM) and on the IBM BG/P Eugene with 262144 cores (“Exterme Scaling Worskop 2010 Report”)
In the project, we investigate the boundary conditions in Nek5000 for exascale computing. The definition of boundary conditions requires special attention, especially for the turbulent boundary layers in the exascale computations. Because only a part of the turbulent spectrum is resolved in the spectral element methods, the challenge is to regenerate and preserve the turbulence at the boundaries. At the inflow boundary, the challenge is to prescribe transient turbulent velocity profiles from DNS data. Simply adding random fluctuations to the DNS profiles lacks the temporal and spatial correlation of real turbulence. The fluctuations must be pre-computed and stored in a database or computed on the fly from an auxiliary computation.