Numerical Study of the Interaction Mechanism of the Juxtaposed Bionic Fishes Using Immersed Boundary Method

The migration movement of fish in regular formation is a common phenomenon in nature. Exploring the principle of hydrodynamics is not only conducive to further understanding the internal mechanism of the fish swarm, but also conducive to optimizing the structural design and formation design of underwater vehicles. The immersed boundary method used in this paper is a non-fitting Cartesian mesh method, which can better deal with the problems of complex geometric shapes and moving boundaries without generating fitting meshes as frequently as the traditional mesh generation method. In this study, a solving program is developed based on the immersion boundary direct force algorithm, which uses multi-grids and non- uniform grids to accelerate the solution of the flow field. The program is verified by a typical example of cylindrical flow, and the corresponding accuracy of the program is demonstrated through comparing the achieved results with that reported in the existing literature. Based on this verified program, the movements of the juxtaposed bionic fishes in incompressible viscous flow are analyzed, the interactions between the movements of fishes and the surrounding flow field are captured, and, importantly, the hydrodynamic mechanism of juxtaposed bionic fishes swimming in a shoal of fish is revealed. Different characteristics of flow fields induced by the juxtaposed bionic fishes’ movements with the same swing frequency but in different phases, namely in-phase and anti- phase, are observed and analyzed. The result shows that the anti- phase scenario is more beneficial to enhancing the overall propulsion performance of the shoal of fish.