Anisotropy of Multiscale Grid Turbulence

Abstract

The effect of the shape of the grid on the decay of turbulence is studied through DNS. We performed simulations of regular, two-scale and fractal grids. The multi-scale grids are characterized by a strong anisotropy in the near field, and these achieve isotropy at the large scales much farther with respect to the single-scale grid. The decay of turbulent kinetic energy (TKE) is affected by the shape of the grid. In the anisotropic region of the fractal grid the decay exponent $m=-2.89$ agrees with the values recently reported in literature. Once the flow achieves isotropy the decay is no longer influenced by the geometry of the grid, and the exponent recovers a value in the classical range $-1.4 \le m \le -1$.