Aerodynamic Drag Reduction by the Trapezoid Spanwise Groove Inspired by Pigeon Feathers

Abstract

Inspired by pigeon feathers, the drag-reducing contribution of spanwise grooves was studied. Surface topography of the wing feather was scanned by an instrument of white light interference. Three types of grooves of triangle, rectangle, and trapezoid were adopted based on the unsymmetric microstructures found on the feather surface. Numerical simulations were conducted to analyze drag-reducing mechanisms. According to the simulation results, the rectangular groove reduced the wall shear stress more efficiently but with greater additional pressure drag, while the triangular groove was the opposite. For the trapezoidal groove similar to the feather structure, drag reduction was the best out of the three. Wind tunnel experiments for the trapezoidal groove were performed by using a cylindrical model and large-area plate. Drag reduction was confirmed from the cylindrical model at a series of velocities from 15 m/s to 90 m/s (about 16% at velocity of 30 m/s and about 8.5% at velocity of 60 m/s). Drag reduction was also obtained from the plate model at a velocity range of 30 m/s to 75 m/s (about 19% at the velocity of 60 m/s), which worked for a wide range of velocity and was more meaningful for the application.