Vortex interaction between self-propelled two tandem flexible fins in wall effect*

It is known that fish can take hydrodynamic advantages by schooling behaviors as well as by wall effects. Inspired by the fish schooling in wall effects, we perform numerical simulations of two tandem flexible fins under the influence of the wall confinements. The movement of the two flexible fins is driven by harmonic heaving motions at the leading edge. The two tandem fins move freely in the streamwise direction by the fluid-flexible body interaction and the motions of the fins are affected by a one sided wall or two sided walls. The vortex interaction between the two fins in wall effects is analyzed as a function of the wall proximity, initial gap distance, bending rigidity, heaving amplitude and phase difference. When the leader and follower have the identical heaving amplitude, the input power of the follower is lower 12%, 19% and 5% near a one sided wall, two sided walls and with no wall respectively than that of the leader. The optimal efficiency of the follower is achieved by changing the heaving amplitude and flapping phase of the follower.