Mixing in swirling jet.

The relationship between the mixing process in a swirling jet and operational parameters Re and Reθ, which are respectively the general Reynolds number based on cross-sectional average velocity in a jet nozzle and the newly defined swirl Reynolds number based on characteristic angular velocity of swirling motion at a nozzle exit, was investigated by measuring concentration distributions of expanding tracer puffs. It is clarified that the increase of Re promotes both radial and axial mixing, and that the increase of Reθ greatly promotes radial mixing but suppresses the axial mixing. Considering the effects of Reθ on the Peclet number, it is made clear that the mixing process is remarkably changed by the generation of reverse flow in a swirling jet.