Three-Dimensional Representation of Streamwise Vortices in a Coflowing Three-Dimensional Wall Jet

Abstract

Perspective view of vortex structure in a fully developed region of a three-dimensional wall jet is reconstructed by applying digital image processing to motion pictures visualized using laser-induced fluorescence. The fluorescence dye was premixed to jet fluid, and a cross section normal to jet axis was illuminated by a thin laser sheet. The time of motion pictures is converted to longitudinal position by Galilean transformation of which constant is a convective velocity of the structure. A fast and memory saving computer program for image stacking is developed to process the pictures by using a personal compuer with a video image memory board. Three-dimensional pictures of vortices indicate that the jet flow is filled with numerous streamwise vortices and that some of them form U-shape bend vortices of which top is inclined to backward and outward. Furthermore, temporal variation of this structure is examined to confirm the applicability of the Galilean transformation.