Droplet release mechanisms: a sensitive subject

Atmospheric scientists have shown that falling water droplets can take on several mode shapes and that the frequency is dependent on the droplet size. However, droplets larger than the capillary length (average dia. < 3 mm) are often neglected because they eventually break-up into smaller droplets. Some have attempted to figure out what the break-up looks like numerically but experimentalists attempting to validate the numerical results have failed, as these break-ups seem to happen in random ways. Here we show through careful experimentation that the release mechanism, geometry and surface conditions play significant roles in the mode and frequency of the droplet after release. The mode and frequency are measured by high-speed camera and radial decomposition. These mode shapes greatly affect when and how the droplet breaks up, indicating that droplet break up is predictable but very sensitive to initial conditions. The largest recorded raindrop is 8.6 mm diameter and here we offer advice on how to make droplets that are nearly spherical when released up to 20 mm in diameter!