Hydrodynamic performance study on a hinge-connected flexible fin by fluid-structure interaction

The hydrodynamic performance of a hinge-connected flexible fin is studied by fluid-structure interaction in this paper. The fin consists of two links, namely, the leading link and tailing link, with various flexibilities. Firstly, the leading link moves with scheduled equation while the tailing link is uncontrolled and subjected to passive motion. The fluid and structure responses of five flexibility groups of links are compared and investigated, and their hydrodynamic responses with different kinematic parameters are detailed analyzed. It is found that the flexibility of links greatly affects the performance of fin and the rigid link-flexible link fin performs better in most simulation cases, while for certain condition, other flexibility groups show advantages, for example, the medium flexible link-medium flexible link fin generates the largest efficiency with low pitching frequency. It is also found that optimal values of thrust force and efficiency can be obtained by choosing the kinematic parameters carefully for specific flexibility group, in which the two optimal values may be not obtained simultaneously. Then both of the leading link and tailing link are actively controlled, and their thrust forces and fluid responses are also compared. The result shows a complex coupling between the fin flexibility and the motions of two links. This study will be useful for the design and control of novel multi-link fin propulsion.