Spray behaviour from non-swirling to swirling gas jet in coaxial atomisation

The present study focuses on the influence of gas swirl on the spray behaviour from a two-fluid coaxial atomiser with high gas-to-liquid dynamic pressure ratios $M$ by varying both the liquid Reynolds number ${\textit{Re}}_l$ and the gas Weber number ${\textit{We}}_g$ . The investigations identify the deviations of the carrier phase velocity fields, droplet distribution, and dispersion when swirl is introduced to the gas phase compared with the non-swirling conditions. The changes in the axial, radial and tangential velocities of the continuous phase due to the introduction of swirl are highlighted while retaining a self-similar behaviour. The slip velocity of the large droplets in swirling sprays is negative, unlike the known positive value for non-swirling sprays. The shape of the radial profiles of the mean drop size is investigated along ${\textit{We}}_g$ , notably revealing an inflection point for swirling sprays at high- ${\textit{We}}_g$ values. A global assessment of the drop size uncovered that swirl leads to its increase for low $M$ while assisting spray formation at high $M$ . Additionally, the radial profiles of axial fluxes for swirling sprays have a wider bell-shaped curve compared with non-swirling sprays at high $M$ , unlike the off-centre maxima found for low $M$ . However, the mentioned dependencies of drop sizes and fluxes cannot be determined by $M$ solely for intermediate gas-to-liquid momentum ratios ( $23\lt M\lt 46$ ), and vary with ${\textit{Re}}_l$ and ${\textit{We}}_g$ . In addition, the response of at least the mean droplets at the edge of the spray to the large gas eddies shows a linear relation with swirl intensity.