An experimental study of the aerodynamics of micro corrugated wings at low Reynolds number

In this paper, an experimental study was performed to examine the flow characteristics of fabricated micro corrugated wings by fully mimicking the real 3D Odonata wing. For this purpose, a true scale hind wing from the Orthetrum caledonicum species with a semi span length of 60 mm was reconstructed by non-destructive close-range photogrammetry and fabricated with an advanced 3D printer. The accuracy of the proposed reconstruction technique was evaluated and compared with a 3D model of the same wing created using a Micro-Computed Tomography (CT) scanning technique to show that the close-range photogrammetry method was able to predict the pattern of micro corrugation of the wings with satisfactory fidelity. To do that, the corrugation patterns of both reconstructed wings were compared at different sections of the wings. Then, high-resolution Particle Image Velocimetry was used to investigate the flow field of the wing during gliding flight at three low Reynolds numbers Re = 5 × 103, Re = 8 × 103 and Re = 12 × 103, and angle of attack 10°. The results include free stream velocity, vorticity distribution, boundary layer, and flow visualization. The velocity contour and vorticity boundary layer of both wings were compared experimentally. The flow behavior around the corrugated patterns reconstructed from both methods were compared with satisfactory agreement. The results support that the corrugations of the wing act as turbulators to generate unsteady vorticity to transition the boundary layer from laminar to turbulent quickly, leading to delayed stall and improved aerodynamic performance. Moreover, this study shows the application of the presented photogrammetry method for corrugated wing reconstruction, which is fast, low-cost, non-destructive, with high replication accuracy for the next generation of micro air vehicles.