Aerodynamic investigation of Passer domesticus inspired biomimetic wing at low Reynolds number

Abstract

A biomimetic wing is designed by considering the wing of a natural flyer ( Passer domesticus) as a reference. Since the birds have thin wings, Bergey BW-3, a thin and highly cambered airfoil, is used to design the wing cross section. To investigate the aerodynamic characteristics of the biomimetic wing, numerical and experimental studies are carried out at low Reynolds number (Re) ranging from 2.5 × 104 to 1 × 105. It is observed that the numerical findings have the similar trend as that of the experimental observations. The performance of the biomimetic wing is compared with rectangular and elliptical wings at Re = 5 × 104. It is observed that the separation bubble formed over the surface of the biomimetic wing at Re = 2.5 × 104 is not strong enough to influence the lift coefficient but increases the drag coefficient dramatically when the mean angle of attack exceeds 18°. It is observed that the drop in the lift coefficient of rectangular wing is higher than that of the other wings due to the presence of sharp edges in the planform. The lowest drag coefficient is witnessed in the elliptical wing but it also has the lowest lift coefficient due to the interaction between the separation bubble and tip vortices. On the other hand, the biomimetic wing offers the highest lift coefficient with a considerable amount of drag. Overall, a 57.9% increase in lift coefficient is observed for the biomimetic wing than that of the elliptical wing under the same conditions. A 22.4% increase in the lift to drag ratio of the biomimetic wing is observed over that of the rectangular wing. It is also observed that the flow separates dramatically as the mean angle of attack increases beyond the stall angle in the rectangular and elliptical wings. But a delay in the flow separation is observed in case of the biomimetic wing after the stall angle. It is also observed that the suction over the wing surface of the biomimetic wing is more at the wing root (fixed end) than that at the wing tip (free end), which may provide good stability during flight conditions. The enhanced aerodynamic performance of the biomimetic wing is due to change in shape of the wing along the span which has a strong influence over its effective angle of attack with respect to the incoming flow.