Swirling dual-disk double-concentric jets at low annulus Reynolds numbers

The flow characteristics and mixing properties of swirling dual-disk double-concentric jets at low annulus Reynolds numbers were studied. The flow patterns, velocity characteristics, and mixing properties were characterized using the laser-assisted smoke flow visualization method, particle image velocimetry (PIV), and tracer-gas concentration detection technique. Three characteristic flow modes,annular jet-dominated wake, central jet-dominated wake, and central jet-dominated radial flow, were observed within different ranges of central jet Reynolds numbers for the annulus Reynolds and the swirl numbers were less than 270 and 0.245. The flow structure of the central jet-dominated wake (a dual-ring recirculation zone in the wake region and two pairs of counter-rotating vortices in the gap between the up- and downstream disks) allowed the annular jet fluids to be transported into the gap between the upstream and downstream disks to premix with the central jet fluids before further being transported to the disk wake. The flow fluctuation intensities in the wake of the central jet-dominated wake were significantly larger than those of the annular jet-dominated wake and central jet-dominated radial flow because the large-scale fluctuation eddies that possess large turbulence kinetic energy existed in the wake. These properties prominently promoted the mixing in the central jet-dominated wake.