VORTICAL AND TURBULENT STRUCTURE OF A LOBED MIXER FREE SHEAR-LAYER

An experimental investigation of the vortical and turbulent structure in a free shear layer downstream of a lobed mixer has been conducted. Pulsed-laser sheet flow visualization with smoke and three-dimensional velocity measurements with hot-film anemometry were obtained for a lobed-mixer configuration and a baseline, planar configuration. Laminar and turbulent initial boundary-layer conditions were documented for both cases. The main result of this investigation is that a new vortex structure was confirmed to exist for the lobed mixer in addition to the well-known streamwise vortex array, consistent with the work of Manning. The normal vortex (due to the Kelvin-Helmholtz instability) sheds periodically from the convoluted trailing edge of the lobed mixer and plays a major part in the enhanced mixing process in combination with the streamwise vorticity. The streamwise vorticity deforms the normal vortex into a pinched-off structure that is unstable and creates intense small-scale turbulence and mixing.