Aerodynamic characteristics of seagull bionic airfoil based on breathable structure

Feathers, as the key component for avian flight, are the core elements constituting the shape of bird wings, and their breathable characteristics significantly influence the aerodynamic properties of bird wings. In this study, feathers were simplified as a breathable structure on the wing surface, and porous medium was applied to the surface of a seagull bionic airfoil to simulate this breathable structure. By utilizing the seepage theory of porous media and employing the Computational Fluid Dynamics (CFD) method, the impact of this biomimetic structure on the aerodynamic characteristics of the airfoil was investigated. The results indicate that, porous medium has a significant impact on the aerodynamic performance of airfoils, and the influence mechanism is analyzed from aspects such as wall pressure distributions, friction drag distributions, and spatial velocity distributions. Under the influence of porous medium, the stall angle of attack of the airfoil increases by 5°, and the maximum lift coefficient is improved by 8.2%. The distribution parameters of porous medium can also significantly affect the aerodynamic characteristics of the airfoil. As the starting point of porous region moves forward, the stall angle of attack increases, while the lift coefficient in the linear segment of the airfoil decreases. As the thickness of porous medium increases, the lift coefficient of the airfoil's linear section decreases, while the drag of the airfoil increases, with a significant increase in the drag of the porous region. The influence of permeable characteristic parameters on the aerodynamic characteristics of the airfoil is significant. As the Darcy number increases, the lift coefficient of the porous airfoil slightly increases, and the drag decreases within a small range of angles of attack but increases in the stall segment. Anisotropy has a minor effect on the lift of the airfoil, but mainly affects its drag. The surface friction drag distributions on the airfoil and in the porous region are primarily determined by permeability in the x-direction. The distribution mode, air permeability characteristics and research conclusions of the semi-covered porous airfoil adopted in this paper can provide certain references for the design and research of bionic airfoils.