Fluid-Structure Interaction Hydrodynamics Analysis on a Deformed Bionic Flipper with Non-Uniformly Distributed Stiffness

Although the biologically flexible flippers of the cormorant (Phalacrocorax) are believed to be one of the most important features to achieve optimal swimming performance before take off, studies on a deformable bionic flipper with a non-uniformly distributed stiffness are rare. In this letter, to gain the unsteady hydrodynamic distribution between flexible aquatic animals and the ambient medium during the power stroke and recovery stroke, the numerical physical model solutions which coupled fluid-structure interaction based on computational fluid dynamics (FSI-CFD) are presented. We quantified the three-axis component distribution, and the results show that the horizontal force of the fluid will not provide positive thrust during the initial take-off stage. Greater lift and forerake moment are generated, which brings the body off the water as soon as possible and reduces the angle of attack. As the angle of attack decreases, the positive thrust will be generated, and the forward velocity and the lift will be further increased. As the draft area of the cormorant is reduced, the wings will start flapping, further increasing the lift and thrust, and thus taking off. The solver in the letter will serve as a framework for the future bio-inspired studies involving active and passive control associated with complex structural materials.