GALCIT Colloquium

Flexible slender structures in flow are everywhere. While a great deal is known about individual flexible fibers interacting with fluids, considerably less work has been done on fiber ensembles — such as fur or hair — in flow. These hairy surfaces are abundant in nature and perform multiple functions from thermal regulation to water harvesting to sensing. Motivated by these biological systems, we consider several examples of hairy surfaces interacting with flow including drinking bats and diving sea otters.  In the first example we consider viscous dipping, a feeding method utilized by many nectar drinking animals. This mechanism is reminiscent of Landau-Levich-Derjaguin (LLD) dip coating, and has been analyzed through the LLD framework in previous studies. However, many viscous dippers have hairy structures on their tongues that enhance fluid uptake. In this study, we investigate the impact of mesoscale hairy structures on feeding efficiency.  In the second example, we take inspiration from semi-aquatic mammals (such as fur seals, otters, and beavers) which have specially adapted fur that serves as an effective insulator both above and below water. Many of these animals have evolved pelts that naturally entrap air when they dive. Here we investigate diving conditions and fur properties which amplify air entrainment.