A Flow Visualization Study of Chaotic Vortical Motion in the Near Field of a Planar Jet

Abstract

A flow visualization-based investigation of the transition of planar submerged water jet shear layers at moderate Reynolds number is presented. The development of the free shear layers under low level artificial excitation was captured on video tape by dye injection flow visualization. Despite “clean” initial conditions and the imposition of periodic excitation, examination of vortex trajectories revealed that the flow structure was not strictly periodic but exhibited “jitter” in the vortex roll-up location and subsequent vortex interaction events. This study focuses on this non-periodic character of the flow. Since even very simple nonlinear systems can exhibit chaotic behavior, the flow visualization images were examined for evidence of whether the observed non-periodic behavior could be associated with chaos. The flow visualization frames were utilized to derive return maps enabling examination of the flow visualization images in pseudo phase space. Results indicate that many aspects of the non-periodic vortical motion show evidence of chaos similar to that exhibited by lower dimension nonlinear dynamical systems.