Junshi Wang

Propulsive Performance of Pitching Panels with Bio-Inspired Passive Directional Flexibility

Thunniform swimming—as displayed by tuna and mackerel—is recognized as fast and efficient. For this study, we have retrieved the first set of high-resolution videos of tuna swimming in two orthogonal directions in sync. From observing tuna swimming, the majority of motion happens within posterior one-third of the body, which mainly consists of peduncle with rotational freedom and flexible caudal fin. It has been shown that choosing the optimal flexibility for flapping aerofoil panel or artificial fin can boost the thrust or efficiency by over 100%, due to change in fin kinematics and wake structure. In this study, the propulsive performance of three different rectangular panels with an aspect ratio of 2 are considered—rigid, chordwise flexible, and spanwise flexible. Free-swimming experiments are performed in a flow tank, from which the self-propelled speed and torque are measured in real time. From this, power and economy can be calculated as a function frequency and amplitude inputs. High-speed videography is taken during swimming and used to reconstruct the kinematics of the panel. With the rigid foil defining a baseline performance, the influence of chordwise and spanwise flexibility are examined and quantified. The results highlight the significant role that chordwise flexibility has on propulsive performance, specifically as it pertains to the economy. Spanwise flexibility does not appear to enhance the performance.