Optimized design and investigation about propulsion of bionic Tandem undulating fins I: Effect of phase difference

Abstract Motivated by the excellent maneuverability and high efficiency of the undulation fishes, a multi-fins propulsor was provided in this article and the propulsion performance was attempted to be improved by taking advantage of the interaction between the tandem fins. The effects of the wave-number and the phase difference were studied numerically. The results showed that the thrust force was enhanced significantly by introducing a fin with wave-numbers of 0.5 at the expense of propulsion efficiency. The vortices induced by the anterior and posterior fins were merged or offset, which depended on the phase difference between the tandem fins. The interaction of vortices led to the variation of thrust force with the phase difference in a sinusoidal curve. With the phase difference around the crest, the propulsion performance of tandem fins was improved clearly. Considering the thrust, lateral force and efficiency, the LL model where both the fin wave-numbers are set to be 1.0 is suitable for the cruising motion of the aquatic vehicle, and the SS model where the wave-numbers are adjusted to 0.5 is beneficial to the fast maneuver. The present results provided a theoretical basis for the design of aquatic multi-fin propulsion robots to meet different task requirements.