Backward injection of liquid jets in crossflow

The effect of the liquid jet injection opposite the airflow direction and its injection angle was studied experimentally and theoretically. Various flow parameters, including trajectory, breakup point and its length, penetration depth, distribution of droplet size, their orientation and aspect ratio, mean diameter of drops, stability of liquid jet column, and oscillation wavelength in different conditions, were measured. Different breakup regimes, column, arc, bag, and multimode, were identified. The gas Weber number, momentum ratio, and backward injection angle were recognized as influencing parameters. Backward injection and reducing its angle by strengthening the effective aerodynamics force and the shear forces created by the interaction of the liquid with the airflow causes more bending of the jet path, faster breakup, smaller droplets, and the resulting improvement of the atomization process. For stability perusal, linear analysis and the theory of the viscous potential flow were utilized. Based on that, a theoretical model was developed for the influence of the backward injection and its angle on the axial and azimuthal wave growth rate of a viscous liquid jet issued into a viscous gaseous crossflow. The interaction of aerodynamic forces, surface tension, viscosity, and momentum makes Rayleigh–Plateau (capillary), Rayleigh–Taylor, Kelvin–Helmholtz, and azimuthal instabilities in the liquid column. Reducing the backward injection angle increases the growth rate and decreases the wavelength of both axial and azimuthal waves. It strengthens K–H waves. The effect of different parameters such as gas and liquid Weber numbers, Ohnesorge number, density ratio, and viscosity ratio was investigated at different injection angles.