Hydrodynamic performance study on a flexible caudal fin

In this paper, a hinge-connected flexible caudal fin model is built and its hydrodynamic performance is examined by fluid structure interaction. The caudal fin includes two links and its flexibility distributes on the two links and the hinge. Five sets of link flexibility are firstly investigated in which the structure and fluid responses are compared and analyzed. It is found that the rigid-flexible fin case exhibits larger structure motions and deformations than other cases, and it can generate larger thrust force in which reverse karman vortex is generated along the pitching cycle. Then the effect of kinematic and flexibility parameters including pitching amplitude, frequency and hinge flexibility are detailed studied by orthogonal experiments, and the thrust force and efficiency are analyzed. It is found that the thrust force and efficiency exhibit a complicated relationship with these factors and different factor level combination achieves the best propulsive performance in each link flexibility set. What's more, optimal performance of thrust force and efficiency are not always achieved simultaneously. The results will be an inspiration for the design and control of novel underwater propulsion mechanism.