Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session T17: Drops: Coalescence
12:40 PM–3:16 PM,
Tuesday, November 23, 2021
Room: North 131 AB
Chair: Sangjin Ryu, University of Nebraska Lincoln
Abstract: T17.00008 : Droplet coalescence in air: formation and expansion of the bridge
2:11 PM–2:24 PM
The second mechanism concerns the expansion of the initial bridge and is determined by the Ohnesorge number (Oh). For usual liquids, Oh is small, and the length of the initial bridge grows at constant speed (inertial regime). The bridge is cylindrical and its longitudinal expansion can be described by the propagation of nondispersive capillary wave packets. At the resolved scale, the interface exhibits slope discontinuities. By considering dihedral potential flows associated with the presence of the slope discontinuities, we show that the apparent angle made by the interface controls the flow rate that enters the bridge and thus determines its radial expansion. For Oh ~1, the initial flow is rapidly attenuated and the connecting bridge between the two droplets adopts a smooth parabolic shape. The maximum interface curvature and the minimum liquid pressure remain at the bridge center. In this case, the expansion is caused by the capillary pressure that drives the fluid toward the center.
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