Bionic Research on Turtle’s Flexible Forelimb Propulsion

In order to investigate the hydrofoil propulsion method, the bionic technology of the turtle’s flexible forelimbs
is studied. Based on the kinematical analysis of turtle hydrofoil, the chordwise deformation characteristics, the reverse
Karman vortex street shedding, and the Strouhal number of flexible hydrofoil are studied, and then the Strouhal number
being between 0.2 and 0.45, the Reynolds number being from 3*10²  to 3*10⁴ are calculated. According to the viscoelastic
constitutive property of turtle hydrofoil, the half-iliac bionic flexible hydrofoil is developed, and its flexibility deformation
as well as tissue mode are analyzed. By use of the underwater bionic experimental sample, the direct navigation and yawing
performance contrast tests of bionic sample with the half-iliac flexible hydrofoil and whole-iliac rigid hydrofoil are conducted
respectively. The experiments’ results show that, however the propulsion efficiency of flexible hydrofoil is higher than the
rigid one only moving at the high value of omega₁ , the sample’s acceleration when propelled by the flexible hydrofoil is higher
than the rigid one all the time. And along with the increasing of omega₁ , the function of flexible hydrofoil to reduce the velocity
vibration of bionic sample, exists and becomes more and more obvious. These experiments’ results provide significant
technical foundation for the control and manipulation study of flexible hydrofoil in the future.