Cormorant Webbed-feet Support Water-surface Takeoff: Quantitative Analysis via CFD

The bio-inspired aerial–aquatic vehicle offers attractive perspectives for future intelligent robotic systems. Cormorant’s webbed-feet support water-surface takeoff is a typical locomotion pattern of amphibious water birds, but its highly maneuverable and agile kinetic behaviors are inconvenient to measure directly and challenging to calculate convergently. This paper presents a numerical Computational Fluid Dynamic (CFD) technique to simulate and reproduce the cormorant's surface takeoff process by modeling the three-dimensional biomimetic cormorant. Quantitative numerical analysis of the fluid flows and hydrodynamic forces around a cormorant’s webbed feet, body, and wings are conducted, which are consistent with experimental results and theoretical verification. The results show that the webbed feet indeed produced a large majority of the takeoff power during the initial takeoff stage. Prior lift and greater angle of attack are generated to bring the body off the water as soon as possible. With the discussion of the mechanism of the cormorant’s water-surface takeoff and the relevant characteristics of biology, the impetus and attitude adjustment strategies of the aerial–aquatic vehicle in the takeoff process are illustrated.