Propulsive Performance Analysis of Underwater Flapping Multi-foil

In recent years, with an increasing interest in the underwater wave glider, which is propelled by converting the ocean wave energy into forward thrust through flapping multi-foil, the flapping-foil aerodynamics has become an important and popular topic of research in the biomimetic field. However, due to the complex marine environment, the wave motion frequency is low and uncontrollable, and the wave amplitude and frequency are non-constant, which make the underwater multi-wing fluttering flow field of the aircraft unsteady. Therefore, it is crucial to study the propulsive characteristics of underwater flapping multi-foil under different conditions. In this paper, hydrodynamics calculation model is built based on the Reynolds-averaged Navier-Stokes (RANS) equation and Realizable model. Two dimensional (2D) NACA foils are applied to establish the hydrodynamic calculation model of flapping multi-foil. The foils are assumed to undergo a combined translational and rotational motion. The unstructured grid was generates by Ansys ICEM. CFD Commercial software Fluent is applied to solve the fluid dynamic characteristics of the flapping multi-foil under various conditions. The results show that flapping multi-foil can produce higher propulsion than a single flapping foil, the interaction of the multi-foil wake was found advantageous for propulsion, it can produce higher propulsion when the distance between the foils is shorter. In this paper, results also show the influence of different factors to the propulsion, which provides a meaningful reference for developing underwater flapping multi-foil vehicle.