Aerodynamic and wake manipulation via structured porous metamaterials on the tip of a NACA0012 airfoil

Blade-vortex interaction (BVI) remains one of the dominant sources of noise in rotorcraft. As BVI noise is inherently linked to the strength and trajectory of tip vortices, controlling the vortex structure at the blade tip presents a promising strategy for passive noise mitigation. In this study, we investigate the influence of permeability-tuned porous tip structures on the aerodynamic performance and flow characteristics of a low-aspect-ratio airfoil. To simplify the problem, a NACA0012 airfoil (chord = 200 mm, span = 200 mm) was vertically mounted on the bottom wall of an open-loop wind tunnel, yielding an effective aspect ratio of 1. A series of lattice-based porous media, representing structured metamaterials, were designed and fixed to the airfoil tip. These structures are periodic and geometrically uniform, enabling their permeability to serve as an independent and equivalent control parameter, thus facilitating analysis from a meta-structural perspective. Aerodynamic forces were measured across a range of angles of attack using a high-resolution load cell at $Re \sim 1.0\times 10^5$. Under identical flow configurations, planar PIV measurements were conducted to visualize and quantify the flow modification induced by the porous tip, particularly in the near-wake region behind the wall-mounted airfoil.