ABSTRACT

The difficulties in laboratory experiments in understanding the vortex dynamics in the region between the grid and that where isotropic turbulence is obtained suggest to perform direct numerical simulations. In this paper flows with analytical inlet disturbances are compared with those obtained by simulating flows past real grids. The results show that the turbulent energy decay rate (q ~ x₁^−m) depends on the shape of the grid. The analysis is focused on analytical disturbances and in particular by considering − 〈Q〉 = 〈s_ijs_ji〉 − 〈ω_iω_i/2〉 and the terms in the U₁ momentum equation written in rotational form. The energy spectra compare well with those in forced simulations, in addition it has been observed that, at the same Re number the multiple scale disturbances generate flows at R_λ higher than those with single scale disturbances.