Quantifying the Effect of Roll on the Propulsive Performance of a Caudal Fin

Biologically inspired propulsion systems have piqued interest in the mechanical engineering field due to their advanced efficiency, agility, and stealth compared to traditional marine propellers. Among the various locomotion strategies employed by aquatic organisms, thunniform swimming - where oscillations are limited to the peduncle and caudal fin - is recognized for its high propulsion efficiency. Up to date, most simplified models of thunniform swimming have been based on pitching and heaving foils. This research aims to elucidate the effect of 3D kinematics on the performance of a caudal fin. Specifically, this study examines the impact of non-zero roll angles on the performance of a pitching rectangular plate. Experiments were performed in a water tunnel facility to measure the plate's thrust generation, power consumption and efficiency. The pitching motion consisted of a sinusoidal movement of 45 degree amplitude. The rolling motion was sinusoidal with roll angles varying within the 0-60 degree range in 5-degree increments. Pitch-roll phase differences from 0 to 90 degrees were used along with frequencies ranging from 0.5Hz to 1.5Hz to test out the coupled pitch and roll motion. The results show that maximum thrust occurs at non-zero roll angle. Generally, the thrust increases from 0-45 degree phase difference and decreases from 45-90 degree phase differences. The flow dynamics of the fin are explored, and the findings are expected to further our understanding of bio-inspired propulsion and inform the design of the next generation underwater vehicles capable of efficient propulsion.