Effects Fin Geometry and Fin Ray Stiffness on the Performance of Bio-inspired Flapping Propulsion

Many examples of flexible surfaces can be found in natural propulsors. Here, we take inspiration from the spiny fin rays exhibited by real tuna fins to alter the flexibility of fin structures on the bio-inspired swimming robot platform, tunabot. This work utilizes a computational model of the tunabot featuring reconstructed body, dorsal, anal, and caudal fin surfaces. Fin geometry, stiffness, and fin ray patterns of the median fins (dorsal and anal fins) are altered to understand the effect on vortex interactions between the median fins and caudal fin, and hydrodynamic force and moment production on the surfaces. Flow information is solved using an in-house developed immersed boundary method based incompressible Navier-Stokes flow solver. Deformations of the fins due to the hydrodynamic forces are computed using Vega FEM. Iterative convergence of the fluid and structure solvers within each time step yields two-way coupled fluid-structure interaction (FSI) simulations. Results in this talk highlight the role of ray stiffness and geometry in altering the hydrodynamic forces of the propulsive caudal fin and undulating body. Furthermore, we will discuss the ability of these fin properties to enhance near-body flow structures. Findings of this research will help inform the design of bio-inspired fins for efficient underwater robots.