2011 Hybrid openMP-MPI turbulent boundary layer code over 32k cores

Abstract. A hybrid OpenMP-MPI code has been developed and opti-mized for Blue Gene/P in order to perform a direct numerical simulation of a zero-pressure-gradient turbulent boundary layer at high Reynolds numbers. OpenMP is becoming the standard application programming interface for shared memory platforms, offering simplicity and portabil-ity. For architectures with limiting memory as Blue Gene/P, the use of OpenMP is especially well suited. MPI communications overhead are also improved due to the decreasing number of processes involved. Two boundary layers are simultaneously run due to physical considerations, represented by two different MPI groups. Different node mappings lay-outs have been investigated reducing communication times in a factor of two. The present hybrid code shows approximately linear weak scaling up to 32k cores