Breakup and Coalescence of Free Surface Flows

Abstract

The picture of a dolphin, jumping out of the water in the New England aquarium in Boston (Fig. 1), gives a very good idea of the challenges involved in the description of free-surface flows. In a complex series of events, which is still not well understood, water swept up by the dolphin breaks up into thousands of small drops. A more detailed idea of what happens close to the point of breakup is given in Fig. 2, which shows a drop of water falling from a faucet. Once an elongated neck has formed, surface energy is minimized by locally reducing its radius, and a drop separates at a point. Once the neck is broken, it rapidly snaps back, forming a capillary waves on its surface. In the last picture on the right, the neck has been severed on the other end as well. Thus in a single dripping event, two drops have actually formed, and the smaller “satellite” drop will subsequently break up to form even smaller drops. This gives a good idea of the complexity of just a single breakup event, driven by surface tension.