Abstract: While the dynamics of the fish tail fin is widely studied, the design of the tail fin propeller lacks a kind of simple valid and estimation method, to link the motion parameters of the tail fin with the propulsive force and efficiency. Based on observation and analysis of vorticity, the flows field structure of 2-DOF tail fin propellers and the thrust formation reason are studied. The ideal propeller theory is applied to the calculation of the propulsive force and efficiency of the tail-fin propulsion. The jet flow and induced velocity is estimated. The function among propulsive force, locomotion parameter and strouhal number is built, as well as the efficiency. The calculation results are in accordance with the observation and experimental results of fish robot. And the calculation method is testified by application in fish robot design.

Key words: Bionics, Efficiency, Propulsion, Robotics-fish, Tail-fin