Hydrodynamic characteristics of a biomimetic propulsor with two oscillating fins in series

In the present paper, a concept design of biomimetic propulsor with two oscillating fins in series to enhance the horizontal mobility of an underwater glider without disturbing glide is proposed. The concept of the serial fins configuration in the propulsor comes from mimicking the mechanism of fish swimming, in which tail fin manipulates head-body generated vortex to form a Reverse Karmon Vortex Street. The propulsor consists of a flapping fore fin acting as a leading edge vortex generator, and a flapping rear fin acting as a vortex manipulator. In order to clarify the hydrodynamic characteristics of the proposed biomimetic propulsor, a series of two-dimensional numerical simulations by solving the Navier-Stokes equations has been carried out. Furthermore, for clarifying the effect of the fore fin on the resultant thrust and efficiency, the results of the serial fins configuration simulations are compared to those of a single rear fin model by just removing the fore fin. It has been confirmed that both thrust and efficiency are increased significantly due to the effect of the flapping fore fin. In addition, the effects of amplitude and frequency that related to the Strouhal number, and phase angle between the two oscillating fins to the hydrodynamic forces and vortex structures are also investigated. It has also been found that the phase angle influences the resultant thrust and efficiency significantly.