Identification and control of large-scale structures in highly turbulent shear flow

Unforced and forced subsonic jets were studied using hot-wire anemometry. It is found that highly coherent flow structure can be generated in the initial region of ducted flow by applying forcing to the flow innstability frequencies. Flow visualization experiments in water showed that the coherent structures had relatively high azimuthal coherence and were periodic in time and space. The convection velocity of the structures was about 60 percent of the mean flow velocity. Mixing of the shear layer with the surrounding recirculation zone and the inside core was enhanced by the forcing and reduced their size accordingly. Photographs from the flow visualization tests are provided.