Primary atomization and breakup regimes of asymmetric impinging liquid jets

We investigate the primary atomization and breakup characteristics of asymmetric impinging liquid jets using high-speed imaging. Two circular jets of unequal diameters and velocities, combined with a controlled angular misalignment, are considered to introduce both momentum and geometric asymmetry. Five distinct breakup regimes are identified over an average Weber number and a momentum ratio range between 101–103 and 0–7, respectively: (i) closed rim, (ii) closed rim with periodic ligament shedding, (iii) capillary rim breakup, (iv) perforation-dominated sheet breakup, and (v) wavy sheet breakup. Regimes (iv) and (v) represent the breakup modes arise due to the coexistence of Rayleigh–Taylor and Kelvin–Helmholtz instabilities under momentum asymmetry. Quantitative measurements such as sheet area, breakup length, sheet width, deviation angle, and oscillation frequency are discussed. The sheet deviation follows inviscid momentum-balance predictions even in highly unstable regimes. These findings establish momentum asymmetry as a critical control parameter in impinging-jet atomization where geometric and kinematic symmetry are rarely achieved.