Dynamics of formation and oscillation of non-spherical drops

Abstract

Present study focuses on the shape of a drop during pinch-off and how the shape of a drop is affected by the flow parameters and different physical properties of the fluids. Both experimental and numerical investigations are performed to unveil the mechanism of non-spherical drop formation and the oscillatory motion of a drop after pinch-off. Numerical simulations are performed over a wide range of density ratios (0.001–0.9) and viscosity ratios (0.01–10) ranging from a gas-liquid system to a liquid-liquid system. The deformation of a drop at the incipience of pinch-off depends on the internal stress distribution within the drop. A larger velocity gradient inside the drop culminates in a stronger shear force within the drop leading to a non-spherical drop during pinch-off. We reveal that the shape of a drop remains either in prolate or in spherical form during pinch-off. A drop undergoes prolate-oblate-prolate oscillation while falling through the surrounding medium. The oscillatory motion is generated due to the local capillary pressure that develops across the drop surface because of the deformed shape of the drop after pinch-off. Present investigation reveals that the deformation of the drop because of the downward pull generated near the pinching region makes the drop shape non-spherical after pinch-off and initiates the oscillatory motion of the drop. The oscillation of a drop reduces substantially at higher relative strength of the viscous force.