PIV STUDY ON WATER SPRAY MIXING IN A CONFINED AIR CROSSFLOW

Abstract

The mixing uniformity of a hollow-cone water spray in an air crossflow is investigated in a rectangular duct by using a particle image velocimetry system. Experiments are carried out with three water/air momentum flux ratios and three nozzle injection angles in the case of a single nozzle. The droplet distributions in both the longitudinal and transverse directions and the velocity vector fields in the transverse direction are obtained. The mixing flow structure along the longitudinal direction has three sequential regions, i.e., vortex controlling, horizontal movement controlling, and impingement controlling regions. The counter-rotating vortex pair (CVP), leading vortex, shear layer vortex, and multiple vortices are observed. The CVP leads to droplet dispersion within a wide range but results in a droplet preferential distribution. A lower water/air momentum flux ratio contributes to a small-scale CVP, while inclined nozzles with an injection angle against the upstream crossflow allow the CVP to occur prematurely. An improved mixing can be achieved with a lower water/air momentum flux ratio and an inclined nozzle with an incidence angle against the upstream crossflow.