Based on the boundary vorticity-flux theory, topology optimization
of the caudal fin of the three-dimensional self-propelled swimming fish
is investigated by combining unsteady computational fluid dynamics with
moving boundary and topology optimization algorithms in this study.
The objective functional of topology optimization is the function of swimming efficiency,
swimming speed and motion direction control.
The optimal caudal fin, whose topology is different from that of the natural fish caudal fin,
make the 3D bionic fish achieve higher swimming efficiency, faster swimming speed
and better maneuverability.
The boundary vorticity-flux on the body surface of the 3D fish
before and after optimization reveals the mechanism of high performance swimming
of the topology optimization bionic fish.
The comparative analysis between the swimming performance of the 3D topology
optimization bionic fish and the 3D lunate tail bionic fish is also carried out,
and the wake structures of two types of bionic fish show the physical nature
that the swimming performance of the 3D topology optimization bionic fish is
significantly better than the 3D lunate tail bionic fish.