Topology and dynamics of flow structures in wall-bounded turbulent flows

Fine-scale structures in a turbulent channel flow and boundary layer at comparable Reynolds numbers are studied through the velocity gradient tensor. The joint pdf of the two invariants of the tensor that characterize the topology of the structures collapse well among these flows under the Kolmogorov scaling in both, the inner and outer layers. However, the averaged time-evolution of the invariant differs among these flows even in the inner layer. This discrepancy is caused by the different effect of the pressure field on the dynamics of these invariants. By using filtered velocity fields, large-scale structures in the outer layer have also been studied. Their topology is similar to smaller-scales, but less intermittency is observed.