The Flow Structures Generated by a Robotic Sea Lion Foreflipper

The sea lion produces thrust by clapping its large foreflippers into its abdomen. As this is significantly different from typical BCF modes of swimming, it is expected that the resulting flow structures will not resemble a reverse von Kármán street. We have conducted flow visualization experiments on a robotic flipper in a static test facility, replicating an animal accelerating from rest. The geometry of the robotic foreflipper is derived from laser scans of a foreflipper of an adult female California sea lion. Dye flow visualizations have produced qualitative data on flow structure formation during sea lion locomotion. Experiments include various flipper clap speeds, flipper locations and dye injection sites. We are gathering quantitative data through particle image velocimetry (PIV) experimentation, eventually comparing this data to live sea lion propulsive capabilities. Using results from the completed dye visualizations, we will be able to determine high priority areas in the wake where we will focus our PIV efforts. Data gathered through PIV will provide greater insight into the mechanics behind sea lion propulsion, moving the project one step closer to its ultimate goal of biological mimicry of a highly developed and efficient underwater propulsion system.