Effect of Flow Interaction between Median Paired and Caudal Fins on Propulsion

In this study, the effects of fin stroke phase offset, flapping frequency, and freestream flow speed on thrust production are investigated for a median paired (pectoral) fin - caudal fin configuration. Fin geometries and kinematics are selected to be representative of common bio-inspired unmanned vehicles as well as the fish that inspire them, and for this study the fins are rigid to limit the variable parameter space. Experimental results demonstrate a significant correlation between freestream flow speed and thrust-optimal stroke phase offset, as well as between fin flap speed and thrust-optimal stroke phase offset. The results also highlight differences between the time-histories of thrust at high- and low-thrust generating stroke phase offsets suggesting a significant difference in wake signatures. This study provides the foundation for development of a comprehensive analtical tool for flapping fin and vehicle design.