A Study of the Vortical Structures of Noncircular Jets

Abstract

Noncircular jets issuing from square, triangular and rectangular orifices are investigated using a flow visualization technique employing laser-fluorescent dye, and controlling vortex evolutions under excitation. In square, triangular, and 2:1 rectangular jets, the corner regions of noncircular vortical structures undergo severe deformation due to self-induced velocity, resulting in the switchover of the geometric axes. The deformation of vortices in a 4:1 rectangular jet is so severe that the major-axis sides come close to each other, collide, and crosslink, and the original single vortex ring bifurcates to two small vortices via the so-called cut-and-connect process. Interactions of two noncircular vortices are affected by self- and mutually-induced velocities, and produce partial merging, vortex stretching, and splitting to small vortices. These results suggest that noncircular jets are very effective in the enhancement of mixing.