Interfacial fluid dynamics inspired by natural systems
Many natural systems interact with the interface between air and liquids on a daily basis. Plants like the lotus that have self-cleaning leaf surfaces and animals that intake fluids in a variety of ways are all examples of these systems. Plants and animals exploit interfacial fluid dynamics in a variety of ways to survive in numerous harsh environments. In this thesis, five studies, inspired by natural interactions with interfaces are presented.
The first study explores the influence of surface wettability in the dynamics of beams struck by water droplets. This study is inspired by raindrop-leaf interaction in nature. We characterize beam behavior after impact using a simple ODE and also find that a hydrophobic cantilever experiences reduced average torque over time than a cantilever with a hydrophilic surface.
In the second study we investigate the fluid dynamics of how dogs lap water with their tongue. Dogs lap because they have incomplete cheeks and cannot suck. When lapping, a dog's tongue pulls a liquid column from the bath, suggesting that the hydrodynamics of column formation are critical to understanding how dogs drink. We measured lapping in nineteen dogs and used the results to generate a physical model of the tongue's interaction with the air-fluid interface. These experiments help to explain how dogs exploit the fluid dynamics of the generated column. The results demonstrate that effects of acceleration govern lapping frequency, which suggests that dogs curl the tongue to create a larger liquid column. Comparing lapping in dogs and cats reveals that, despite similar morphology, these carnivores lap in different physical regimes: a high-acceleration regime for dogs and a low-acceleration regime for cats.
In the third study how bats drink on the wing is investigated. Bats are unique in nature in that they are one of the only animals that ingest fluids during non-hovering flight. This behavior has the advantage that bats can drink and maintain flight while hunting for food. We find that bats simply extend the tongue and drag it on the water surface while flying. The bats ingest water that coats the inside of the mouth and tongue after removal from a water bath. Bats also change their wing-beat pattern to avoid hitting the water.
We investigate the crown splash instability formed when a rounded rod impacts a fluid bath. The crown splash has been widely studied; however, it has not been seen in the configuration we present. When a rounded rod impacts water, it displaces fluid, and that fluid forms a lamella that climbs up the side of the rod. Depending on the speed of impact, rod size, and other fluid parameters an instability similar to a crown splash forms. In this study, we characterize the growth of the fluid lamella along with the wavelength of the instability.
Finally, we investigate the dynamics of squeezed fluids inspired by clapping wet hands. When water splashes, numerous water droplets, rather than fluid threads, are dispersed. This squeezing motion of the hands makes the fluid in between eject and eventually break into drops. In this study, the trajectory of a rim formed by fluid squeezed between two plates is measured and captured by a theoretical model. Additionally, the spacial distribution of the rim perturbation is predicted using Rayleigh-Plateau instability theory.