Abonnement à la biblothèque: Guest
TSFP DL Home Archives Comité de direction


Paolo D'Addio
Dipartimento di lngegneria Meccanica e Aerospaziale Universita La Sapienza Via Eudossiana 16, I-00184, Roma

Paolo Orlandi
Department of Mechanics and Aeronautics, "Sapienza" University of Rome, Via Eudossiana 18, 00184 Rome, Italy


The decay of isotropic turbulence generated by grids was widely studied in the past, and the influence of the shape of the grid is still not fully understood. In the present work the effect of multiscale grids have been analyzed with the aim to investigate the behavior of fluid structures. A good agreement has been found with the wind tunnel experiment of Veeravalli & Warhaft (1989) and, despite the different Reynolds number, all the phenomena are well reproduced by DNS. The turbulence mixing layer is highly intermittent, suggesting the displacement of flow structures between the two homogeneous layers. The flow generated by the grid with the higher mesh ratio is dominated by one scale, while the flow relative to the grid with the smaller mesh ratio is controlled by two scales. The presence of a lengthscale gradient gives rise to the stress (uv). Flow visualizations of the vorticity field show that the square structures immediately behind the grid become circular before rolling-up, and that these structures survive longer for multiscale grids. The longitudinal, transverse and cross spectra show a persisting anisotropy for multiscale grids, permitting to the flow to survive longer with respect to singlescale grids. Therefore a flow with a high Rλ can be generated.