Sea Lion Swimming and Ship Air Wake Research, Two Projects at the George Washington University

Sea Lion Swimming:
The main objective of this research is to explore a mechanism for underwater propulsion that leaves little traceable wake structure while producing high levels of thrust. A potential  biological model is the California sea lion, an aquatic mammal that produces thrust primarily using its foreflippers, unlike most marine swimmers which use caudal fin oscillation. Sea lions use a “clap and glide” method which appears to have no characteristic frequency and thus are expected to generate a significantly different wake. In an effort to build a robotic sea lion flipper for water tunnel experimentation, flipper kinematics have been quantified for the first time in both two and three dimensions, and the flipper’s geometry has been extracted using three non-invasive methods which will be briefly compared for their overall quality and level of detail captured.
Ship Air Wake:
Shipboard launch and recovery of naval rotary wing aircraft is vital to several of the Navy’s mission areas, but is considered challenging and potentially dangerous, often limited by rapidly changing flow conditions due to ship motion, air turbulence created by the ship’s superstructure, and the dynamic interaction between the vessel’s air wake and the rotor wake. This talk will present comparison between detailed in situ air wake measurements on a 32.9 m (108 ft) long Navy vessel, and both wind tunnel and CFD results (with matching Reynolds numbers), in an attempt to validate computations for reducing the required flight testing. Preliminary results from in situ dynamic interface experiments will also be presented, with a scaled RC helicopter producing an equivalent rotorcraft wake while mounted on a pole at a representative height.