Volumetric Analysis of Fish Swimming Hydrodynamics using Synthetic Aperture Particle Image Velocimetry

This thesis details the implementation of a three-dimensional PIV system to study the hydrodynamics of freely swimming Giant Danio (Danio aequipinnatus). Volumetric particle fields are reconstructed using synthetic aperture refocusing. The experiment is designed with minimal constraints on animal behavior to ensure that natural swimming occurs. Resultantly, the fish exhibits a variety of forward swimming and turning behaviors at speeds between 1.0-1.5 bodylengths/second. During these maneuvers, the imaging system is also used to track and reconstruct the fish body. The resultant velocity fields are used to characterize the size and shape of the vortex rings shed by the fish during forward swimming and turning. Results show clearly isolated and linked vortex rings in the wake structure, as well as the thrust jet coming off of a visual hull reconstruction of the fish body. Depending on the maneuver, the amount of symmetry in the wake varies, emphasizing the shortcomings of a single planar slice to characterize these behaviors. The additional information provided by volumetric measurement is also used to analyze the momentum in the fish’s wake. The circulation of the vortex rings is computed across several slices of the ring taken through its center axis and analyzed over time. Circulation can be used to compute the fluid impulse in the vortex ring to better understand propulsive performance. The measured impulse, combined with visualization of the wake, provides a comparison between forward swimming and turning based on volumetric measurements. The development of this system lays a foundation for further volumetric studies of swimming hydrodynamics. Thesis Supervisor: Alexandra H. Techet Title: Associate Professor of Mechanical and Ocean Engineering