Abstract: Fishes that rely on fin undulating motion to propel themselves usually have an extraordinary stability and maneuvering. Among them, the propulsion patterns are generally divided into two types according to the amplitude envelop formation of travelling wave, i.e. amplitude gradually increases from anterior to posterior and amplitude that stay consistent along the fin. A biomimetic pectoral fin of bluespotted ray is developed, and an experiment is implemented to investigate the differences of thrust between the two propulsion patterns under different undulating frequency, amplitude and wavelength. The experimental results illustrate that the propulsion thrust mainly increases with the increase of undulating frequency, amplitude and wavelength under both propulsion patterns. However, the thrust generated under the pattern with amplitude gradually increases from anterior to posterior is always larger than the one generated under the pattern with amplitude that stay consistent along the fin under the same kinematic parameters. Thus, for a further investigation to the experiment observations, a two dimensional biomimetic pectoral fin model is established. By taking advantage of finite volume method(FVM), the model and its corresponding computational region were dissociated. Then, the propulsion thrust of the two patterns is calculated based on computational fluid dynamic(CFD). A comparative analysis of thrust generation under different frequency, amplitude and wavelength is carried out. Finally, the pressure contour and vortex distribution in the wake of the fin is illustrated. The current findings are used for propulsion pattern selection of biomimetic fin to achieve efficient and reliable application.

Key words: Biomimetic fin, Computational fluid dynamics(CFD), Kinematics, Simulation, Undulating pattern