Step onset from an initial uniform distribution of turbulent kinetic energy.

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We consider the time decay of a field with an initially uniform turbulent energy distribution where the macroscale has been slightly varied in two adiacent regions. The flow is studied by means of Direct Numeical Simulation carried out in a parallepiped, see fig. 1 b. The interesting observation is that the time evolution of the field shows the onset of a step of turbulent energy. It is sufficient to introduce a slight dishomogeneity associated to the integral scale that the nonlinear interaction is able to induce a dishomogeneity also in the kinetic energy. We present here a set of results from experiments where we actually follow the temporal decay of two isotropic turbulences (of initial equal turbulent kinetic energy, but of different integral scales) that macth over a thin region Δ(t). The two isotropic regions are characterized by a different shape of the spectrum in the low wavenumber range, as shown in figure 1, see , a thing which was obtained by means of a high-pass filter (see [5]).KeywordsTurbulent Kinetic EnergyDirect Numeical SimulationIntegral ScaleIsotropic TurbulenceScale GradientThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.