Time-resolved evolution of wall-bounded direct and inverse cascades in turbulent channels at Reτ = 4000

Resumen

The temporal evolution of the structures responsible for the momentum transfer in a turbulent channel at Reτ = 4000 is studied using DNS sequences with temporal separations among fields short enough for individual objects to be tracked. Direct and inverse physical cascades are associated with the process of structures splitting and merging respectively. It is found that the direct cascade predominates, but both directions are roughly comparable. Most of the merged and split fragments have small sizes of the order of some Kolmogorov units. However, an inertial self-similar process is found in which the structures merge and split in fragments of comparable sizes. Finally, a link is established between places with high Reynolds stresses and the predominance of either the direct or the inverse cascade.