Axisymmetric numerical simulation of a conducting drop impact onto a deep pool under a vertical uniform magnetic field: Vortex rings and swinging jets

We numerically investigate the impact of an electrically conducting drop on a deep pool of the same liquid under an external vertical magnetic field. An improved volume of fluid method and adaptive mesh refinement are employed in an axisymmetric coordinate system to maximize computational efficiency. The induced Lorentz force is treated as an external body force. In a wide range of Reynolds numbers (Re∈[700,12 000]) for varying Weber numbers (We∈[40,500]), we categorize the impact phenomena into three categories: no vortex shedding, main vortex shedding, and Kármán vortex street. Thus, a phase diagram is provided in aspects of vortex structures and jet morphologies. The increased magnetic field or surface tension always acts to restrain splash. They can both exhibit a transition from no vortex shedding to main vortex shedding. However, surface tension in the higher Reynolds number region suppresses all kinds of ejecta strongly. Still, it has little impact on vortex rings, while the vertical magnetic field affects vortex rings and decelerates the global outward radial movement of splash jets. Interestingly, as the vortex ring continuously sheds at the two extreme points of curvature and a Kármán vortex street emerges, the first emerged jet ejecta tends to swing between the narrow gap near the neck region. Its gradually slowing down swing frequency correlates with the von Kármán vortex street strongly. Finally, results demonstrate that vertical magnetic fields have non-monotonic effects on swings of the ejecta at the beginning when the jet happens.