Investigating the effects of leading-edge tubercles on the aerodynamic performance of insect-like flapping wing

Abstract

Tubercles are small protuberances or bumps on the leading edge of humpback whale's pectoral fin. To examine the effects of leading-edge tubercles on the aerodynamic performance of a flapping wing, lift, drag, and power coefficients are obtained from numerical simulations. A revolving wing (one-degree-of-freedom azimuth rotation; rotation in a horizontal plane after an initial acceleration) with leading-edge tubercles at an angle of attack of 40° and Reynolds number of 400 is used in the present study. The reason for choosing azimuth rotation is that it resembles downstroke and upstroke of flapping motion of an insect. A rigid rectangular wing with six different combinations of wavelengths (λ = 10% and 50% of the chord length) and amplitudes (A = 2.5%, 5%, and 10% of the chord length) are chosen for this study. These parameters are inspired by the tubercles present at the leading edge of humpback whales' pectoral fin. It was observed that generally, tubercles degraded the aerodynamic performance of the wings in terms of lift, drag, and power coefficients. Although some of the tubercle leading-edge wings showed lower drag (2.20% lower) and lower power coefficient (2.12% lower) values than the baseline wing, none of the tubercle wing performed better than the baseline wing in terms of aerodynamic performance parameters; aerodynamic efficiency ( $\overline{C_L}/\overline{C_D}$ ) and power economy ( $\overline{C_L}/\overline{C_D}$ ). Hence, it was concluded that the tubercles are not advantageous over the straight leading-edge wing for azimuth rotating hovering insect-like motion and further investigation is required to explore its potential benefits.