Significance of localized vortical disturbances in wall-bounded and free shear flows
Seminar Room 1, Newton Institute
The resemblance among coherent structures naturally occurring in fully developed bounded turbulent shear flows, transitional flows and free shear layers suggests the existence of a basic mechanism responsible for the formation of the structures under various base flow conditions. The common elements in all such flows are the shear of the base flow and the presence of a localized vortical disturbance within this shear. Due to their localization in space, the surrounding base flow can be assumed to have homogeneous shear to leading order. In this talk we combine analytical, numerical and experimental tools to show that indeed the interaction between a localized dipole-vortical disturbance and the surrounding `simple' laminar shear flow where the velocity vector is (at most) a linear function of the coordinates, can reproduce the generation mechanism and characteristics of the coherent structures that naturally occur in turbulent bounded shear flows (counter-rotating vortex pairs and hairpin vortices) and free shear layers (`rib vortices').