Hydrodynamic Performance of Deformable Fish Fins and Flapping Foils

A computational study of fish fin hydrodynamics is being conducted concurrently with experimental analysis. The presence of a complex shaped moving boundary makes this a difficult proposition for computational fluid dynamics and here we use a Cartesian grid based immersed boundary solver designed to handle such flows in all their complexity. High resolution, high speed video of fish fin movement during steady swimming by a bluegill sunfish (Lepomis macrochirus) is obtained and these are used as a basis for developing a high fidelity geometrical model of the flapping fish fin. Simulations are carried out in order to examine the hydrodynamic performance of the fish fin and understand the wake topology of such fins. The fin motion is highly complex and a number of different strategies including proper orthogonal decomposition of the fin kinematics are used to examine the various kinematical features of the fin motion as well as their impact on the fin performance.