Unveiling crown-finger instability of a non-spherical drop impacting a liquid surface

We present a three-dimensional numerical study of the splashing dynamics of non-spherical droplets impacting a quiescent liquid film, covering a wide range of aspect ratios (Ar) and Weber numbers (We). The simulations reveal distinct impact dynamics, such as spreading, cusp formation, splashing, and canopy formation, which are delineated in a regime map constructed in the Ar–WeS.B. acknowledges ANRF for the financial support through the grant ANRF/IRG/2024/000711/ENS and the computational resources provided by PARAM Seva under the National Supercomputing Mission, Government of India. parameter space. Our results demonstrate that droplet morphology during the impact significantly influences crown evolution and splash initiation, with oblate drops promoting fingering and fragmentation due to enhanced rim deceleration, while prolate drops tend to form canopies. We observe that the hole instability, which becomes more prominent at higher Weber numbers, arises from lamella rupture in the thinnest region of the film, located just beneath the crown rim. A linear stability analysis, supplemented by the temporal evolution of the crown obtained from the numerical simulations, adequately predicts the number of fingers formed along the crown rim by accounting for both Rayleigh–Plateau and Rayleigh–Taylor instabilities. The theoretical analysis demonstrates the dominant role of the Rayleigh-Plateau (RP) instability in determining the number and wavelength of early undulations, with the Rayleigh-Taylor (RT) instability serving to amplify the growth rate of the disturbances. Our findings highlight the critical role of the droplet shape in splash dynamics, which is relevant to a range of applications involving droplet impact.