Enstrophy production and dissipation in developing grid-generated turbulence

Direct numerical simulations are performed to investigate the spatial evolution of small-scale motions in turbulence behind a single square grid. Some aspects of small-scale motions, which are thought to be universal, are examined at different streamwise locations along the centerline. The behavior of small-scale motions at the end of the simulation region resembles the well-known behavior observed in many types of turbulence (e.g., homogeneous isotropic turbulence, fractal-generated turbulence, and plane jet), whereas in the near grid region, the turbulence exhibits quite different properties. For instance, the alignments between the vortex vector and the eigenvectors are relatively weak in the upstream location. In contrast, at the furthermost downstream location, the alignments are close to the case of homogeneous isotropic turbulence. Also, it is demonstrated that the high enstrophy region may not be indispensable for the appearance of the 2/3 power-law at a streamwise location close to the grid. (C) 2016 AIP Publishing LLC.