Vortex Clusters and Their Time Evolution in High- Reynolds-Number Turbulence*

Time series data (with a time interval of $4\tau_\eta$) obtained by high-resolution direct numerical simulations (DNSs) of forced incompressible turbulence in a periodic box, with a maximum of $12288^3$ grid points and Taylor micro-scale Reynolds numbers $R_\lambda$ up to $2300$, are used to study the vortex dynamics in high Reynolds number ($Re$) turbulent flows. Here $\tau_\eta$ is the Kolmogorov time scale. A visualization method to handle such large-scale data was developed for this study. In the high $Re$ turbulence generated by the DNS, we observed the dynamics of tube-like vortex clusters of various sizes, which are constructed by strong micro vortices. For example, we observed the generation of the tube-like clusters of various sizes and the processes of their merging and breakdown. We also observed layer-like vortex clusters of the order of the integral length scale forming shear layers in the high $Re$ turbulence.