Analyzing the effect of fin morphology on the propulsive performance of an oscillating caudal fin using a robotic model

A bio-inspired robotic underwater vessel was developed to test the effect of
fin morphology on the propulsive performance of caudal fin. The robotic vessel, called The
Bullet Fish, features a cylindrical body with a hemisphere at the forward section and a
conical body at the stern. The vessel uses an oscillating caudal fin for thrust generation.
The robotic vessel was tested in a recirculating flume for seven different caudal fins that
range different bio-inspired forms and aspect ratios. The experiments were performed at
four different flow velocities and two flapping frequencies: 0.5 and 1.0 Hz. We found that
for 1 Hz flapping frequency that in general as the aspect-ratio decreases both thrust
production tends and power decrease resulting in a better propulsive efficiency for aspect
ratios between 0.9 and 1.0. A less uniform trend was found for 0.5 Hz, where our data
suggest multiple efficiency peaks. Additional experiments on the robotic model could help
understand the propulsion aquatic locomotion and help the design of bio-inspired
underwater vehicles.