Aerodynamics of a three-dimensional bionic morphing flap

Avian wings are characterized by intricate feather movements to manipulate airflow and enhance aerodynamic performance. The wing trailing-edge undergoes continuous gradual transformations to enact camber reflexes. A three-dimensional bionic flap inspired by the avian wings is proposed. The flap undergoes spanwise morphing to generate seamless wave-like deformations at the trailing-edge. The performance of S809 airfoil fitted with various spanwise morphing flaps, and conventional flaps, is studied. Comprehensive investigations are performed to analyze the aerodynamic forces, pressure-fields, and velocity evolution across the airfoils fitted with different flaps, subjected to various deflection angles and angles of attack, at the Reynolds number of 10⁶. The analyses exhibit significance of variable mean airfoil-camber on the aerodynamic performance. Comparative analyses demonstrate the superiority of morphing flaps over the conventional ones with regards to- lift increment, drag reduction, and enhanced glide ratio. Further, flow-field visualization and surface-flow measurements reveal unique 3D-evolution of the inflow in streamwise and spanwise directions. The spanwise morphing significantly delays flow separation and aids turbulence suppression. The downstream wake-velocity profiles are also found to be considerably reformed by the spanwise morphed flap topology. Overall, the study establishes supremacy of spanwise morphing over the conventional design in terms of achieving optimal aerodynamic performance.