Taking a Free Ride – Exploring the Hydrodynamics of a Bio-inspired Vessel Swimming Behind an Obstacle

Experiments and numerical models have shown that fish can take advantage of vortex sheds from other swimmers or obstacle. Bio-inspired vessels could exploit similar hydrodynamics interactions to minimize energy and enhance maneuvering. In this wok, we used a 40% scale down model of a bio-inspired underwater robotic to study the hydrodynamics when position behind an obstacle. The physical model -- composed of an ellipsoidal body and a fixed ventral fin, was tested in a recirculating flume. The model was attached through the flat plate, perpendicular to the flow, using fishing line. The dynamics of the vessel were recorded for different flat plate widths and flow speeds while releasing the vessel from different distance relative to the obstacle. In addition, Particle Image Velocimetry was used to measure the flow field between the flat plate and the vessel. Through these experiments we found that the flat plate creates a specific region behind it where the model oscillates with the formations of the von Karman Vortex Street and at certain distances even accelerates into the plate. These hydrodynamics interaction could be exploited by single or group of underwater robotics to enhance efficiency or even find stable configurations between them.