Numerical Study Relevant for Proper Design of Experiments on Swimming-fish Hydrodynamics

It has always been attractive for researchers to observe and understand the fish swimming behavior in water. A large number of real-fish tests has been carried out by biologists in swim tunnels with the focus on estimating accurately fish metabolic rate. The space between the fish and boundary walls of the tunnel is often limited, leading to potential wall effects on swimming performance from hydrodynamic perspective. Besides, there have been many experimental and numerical studies on a deformable body fixed in its position in a uniform current or tethered with the opposite velocity in a quiescent fluid. However, for the actual locomotion of the self-propelled fish, the undulatory deformation of the body might cause recoil reactions and then change the overall performance. This work aims to compare behaviors between a freeswimming fish and a undulatory fish fixed in current, as well as investigate the influence of the experimental setup on fish's hydrodynamic performance. Numerical simulations have been carried out based on a two dimensional fish-like foil. A self-propulsion function for flexible bodies has been implemented within the OpenFOAM library. As main results, the time-averaged forward swimming speed, fish locomotion and wake patterns have been obtained and analyzed.