Thrust producing mechanisms in ray-inspired underwater vehicle propulsion

Abstract

This paper describes a computational study of the hydrodynamics of a ray-inspired underwater vehicle conducted concurrently with experimental measurements. High-resolution stereo-videos of the vehicle’s fin motions during steady swimming are obtained and used as a foundation for developing a high fidelity geometrical model of the oscillatory fin. A Cartesian grid based immersed boundary solver is used to examine the flow fields produced due to these complex artificial pectoral fin kinematics. Simulations are carried out at a smaller Reynolds number in order to examine the hydrodynamic performance and understand the resultant wake topology. Results show that the vehicle’s fins experience large spanwise inflexion of the distal part as well as moderate chordwise pitching during the oscillatory motion. Most thrust force is generated by the distal part of the fin, and it is highly correlated with the spanwise inflexion. Two sets of inter-connected vortex rings are observed in the wake right behind each fin. Those vortex rings induce strong backward flow jets which are mainly responsible for the fin thrust generation.