Influence of swirl on gas-liquid coaxial atomization in high-pressure environments

We present recent experimental results on the dynamics of atomization of a liquid column by a coaxial turbulent gas jet, under varying gas angular momentum (swirl) conditions and densities. We compare between atomization under atmospheric conditions and in a 5 bar environment. For both pressure conditions, the parameter space includes a gas-to-liquid momentum ratio in the range of M = 25–56 and swirl ratios of SR = 0-1. High-speed shadowgraphy images are used to quantify the liquid-gas interface in the spray near-field. In the mid-field, Phase Doppler Particle Analyzer (PDPA) measurements quantify the droplet sizes, velocity distributions, and their radial variations across the spray. At high pressures and increasing M, we observe a decrease in spray angles at SR = 0, but an increase in spray angles when SR > 0.5. We reconcile these observations with the crown de-wetting mechanism. First observed in X-ray shadowgraphs of the spray, crown de-wetting is found to depend on the gas inertia relative to the liquid (gas density increases linearly with atomization environment pressure), potentially switching behavior. This leads to the altered spray angle trends observed, and modified droplet radial distributions in the mid-field, which are characterized via the PDPA measurements.