Aerodynamic characteristics of seagull bionic airfoil based on breathable structure

Feathers are a critical component for avian flight, serving as the core structural element that defines wing morphology. Their inherent permeability is also a significant factor influencing the aerodynamic characteristics of bird wings. In this study, the permeable structure of feathers was simplified and modeled as a porous medium applied to the surface of a seagull-inspired airfoil to simulate realistic permeability effects. Based on seepage theory for porous media and employing computational fluid dynamics (CFD), the impact of this biomimetic configuration on the aerodynamic performance of the airfoil was investigated. The results demonstrate that the porous medium significantly alters the aerodynamic behavior of the airfoil. Specifically, it increases the stall angle of attack by 5° and enhances the maximum lift coefficient by 8.2%, primarily through modifications in wall pressure distribution, surface friction drag distribution, and spatial velocity distribution. Regarding geometric parameters, shifting the starting point of the porous region forward increases the stall angle but reduces the lift coefficient in the linear region. Increasing the thickness of the porous medium reduces the lift coefficient in the linear region and elevates the overall drag, with a pronounced increase in drag within the porous region itself. In terms of permeability parameters, a higher Darcy number slightly improves the lift coefficient, reduces drag at low angles of attack, but increases drag in the stall region. Anisotropy has a minor effect on lift but significantly influences drag characteristics. The surface friction drag distribution on the airfoil surface and the drag in the porous region are predominantly governed by the streamwise (x-direction) permeability. The distribution pattern, permeability characteristics, and findings presented in this study on partially porous-covered airfoils can provide valuable insights for the design and research of biomimetic airfoils.