Instability mechanisms of the bag-stamen breakup

This experimental study explores the breakup behavior of a liquid drop and examines the underlying instabilities that govern the bag-stamen breakup regime. The deformation caused by the pressure field initiates a circumferential wave along the equatorial region of the drop, and its amplification is governed by the Kelvin–Helmholtz instability mechanism. This leads to restructuring of the drop into a bowl shape. As air accelerates into the bowl, meridional waves develop that later evolve into the stamen root. The evolution of the stamen across varying Weber numbers reveals three distinct breakup submodes: (i) surface tension-mediated stamen breakup, (ii) axis-switching-mediated stamen breakup, and (iii) Rayleigh–Taylor driven stamen breakup. The first submode is mainly influenced by the Rayleigh–Plateau instability, while the latter two are dominated by axis-switching and Rayleigh–Taylor mechanisms, respectively. Radial elongation of the rim reduces its diameter, with the instantaneous local Bond number remaining of order unity, highlighting the influence of the Rayleigh–Plateau instability. Furthermore, the coalescence of the rim with the receding bag rim results in a localized disturbance that eventually induces corrugation. Due to the capillary effect, liquid from the surrounding rim recedes into these corrugations, promoting ligament formation, which subsequently destabilizes and sheds droplets. The droplets formed after rim breakup, due to radial elongation, are significantly smaller than the capillary length scale. This underscores the critical role of the bag rim and rim collision in amplifying the overall disintegration process.