MPI Scalability of a Large Memory LES Code

Large eddy simulations (LES) of co-flowing round jets with 33.6 million grid points are carried out using 16 Sun 1 GHz UltraSPARC III Cu processors. An in-depth processor scalability analysis is carried out for an MPI based code for a finite-volume solution of time dependent Navier-Stokes equations. The solver is based on a second-order structured staggered grid discretization, second-order time advancement, and a multi-grid Poisson equation for pressure. Particular attention is paid to the effect of initial conditions on the spatial development of the co-flowing jet at a Reynolds number of 7,300. A co-flow velocity to initial jet centreline velocity ratio of 1:11 and a coflow to initial jet diameter ratio of 35:1 are used to match the flow cases of [12]. The simulation volume, where is the orifice diameter at the jet inlet, is divided into control volumes in the longitudinal, radial and azimuthal directions respectively. Time averaged results of the effect of initial conditions on mean flow, the decay of jet centreline velocity, growth of the jet and the distribution of Reynolds stresses in the near and far field of the shear layer are presented. These quantities show good agreement with the measurements of [12]. The evolution of the turbulence structures is quantified using various discrimination techniques, and when compared with the flow visualisation experiments of [15], both techniques are observed to extract similar topological features.