LAUDER*, G.V.*; MADDEN, P.; MITTAL, R.; DONG, H.; BOZKURTTAS, M.; DAVIDSON, N.; TANGORRA, J.; HUNTER, I.; Harvard Univ.; Harvard Univ.; George Washington Univ.; George Washington Univ.; George Washington Univ.; Massachusetts Institute of Technology; Massachusetts Institute of Technology; Massachusetts Institute of Technology: Pectoral fin function in sunfish: experimental hydrodynamics, computational fluid dynamics, and construction of a robotic model

Fishes are noted for their ability to maneuver and position themselves accurately even in turbulent flows. This ability is the result of the coordinated movement of fins which form flexible control surfaces that allow thrust vectoring. We have embarked on a research program designed to understand the dynamics of pectoral fin function in sunfish (Lepomis macrochirus) and to construct a robotic pectoral fin thruster. We used digital particle image velocimetry (DPIV) on the fins of freely swimming fishes and computational fluid dynamics (CFD) to calculate flows based on measured 3D kinematic data. DPIV experiments used a stereo configuration, transverse plane orientation, and high sample rate (500 fps) to capture streamwise vorticity and to reconstruct time-dependent fluid momentum changes in three dimensions. Both DPIV and CFD data demonstrate that the fin can generate thrust throughout the fin beat. Two simultaneous attached leading edge vortices are present as the fin cups laterally during abduction. A proper orthogonal decomposition (POD) of fin kinematics allowed identification of three primary modes of fin motion which were used individually and in combination to calculate fin flows and study the relationship between kinematic and hydrodynamic performance. Thrust is generated by a combination of an accelerating spanwise wave, cupping of the fin surface during abduction, and area increase during fin retraction. A first generation robotic model of the bluegill sunfish pectoral fin has been developed that can reproduce the complex pectoral fin motion.