Experimental study on the effects of trailing edge geometry and pitching amplitude on the wake structure of bio-inspired pitching panels

Some aquatic swimmers create thrust with a caudal fin or a fluke found at the rear of the animal. These surfaces display many geometries, including those with different trailing edges. In the current work, the effects of systematically varying the trailing edge shape are studied using phase and time-averaged velocity fields obtained from stereoscopic particle image velocimetry in a water tunnel experiment. Results focus on the three-dimensional wakes produced by panels with straight, forked, and pointed trailing edges pitched at multiple amplitudes for Strouhal numbers, St, between 0.22 and 0.53. Results show that geometry and St influence wake behavior and dynamics. Portions of the phase-averaged wakes are often comprised of linked vortex rings, formed by greater amounts of vorticity as St number is increased. The time-averaged wakes indicate that increasing St leads to an injection of more momentum into the flow. In general, pointed trailing edges appear to generate more vorticity and momentum than straight and forked trailing edges.