On the Hydrodynamics of Anomalocaris Tail Fins

Abstract

This thesis examines the hydrodynamic performance of a tail-fin abstraction of Anomalocaris canadensis, a large arthropod from the Cambrian period believed to have been an apex predator. Through direct force measurements and stereoscopic particle image velocimetry, it was found that a flat plate with a multi-vane geometry inspired by preservations of Anomalocaris exhibited a region of enhanced steady-state lift and drag at angles of attack greater than 25° when compared to an equivalent delta-wing plate. These shapes showed little difference during acceleration from rest; however, at an angle of attack of 30°, the lift and drag measured on the multi-vane model were 15.3% and 17.0% higher than the delta-wing model, respectively. It was found that the secondary and tertiary vanes of the tail-fin abstraction encourage the formation of additional leading-edge vortices, similar to those frequently seen on natural propulsors. The formation of these additional leading-edge vortices is confirmed by the increase in streamwise circulation measured using particle image velocimetry near the additional leading edges along the length of the chord. The results of the current study suggest that the enhanced resultant normal force on the tail fin of Anomalocaris made it well-suited for manoeuvres, giving it the ability to turn quickly and through small radii of curvature.