Meeting Abstract
The leading-edge vortex (LEV) is a canonical aerodynamic mechanism in the flapping flight of insects, mammals, and birds across a variety of scales. While the in vivo LEV in insects is a coherent vortex that remains bound to the wing near the leading edge (with a diameter less than 50% the local chord length), in laboratory models with rigid wings this coherence is disrupted and the vortex grows (exceeding 80% the local chord length), a phenomena known as bursting. Bursting has been shown to reduce LEV lift, but it remains unknown how this impacts insect flight performance. Additionally, insect wing flexibility is known to increase lift. Its impact on vortex structure is unexplored, but its known role in force production suggests that flexibility distribution in insect wings could contribute to maintaining higher-lift unburst LEVs. To test this, we mounted freshly removed Manduca sexta wings on a motor rotating at a constant velocity to generate coherent LEVs at Re O(103) and observed the fluid structure with smoke visualization. Freshly mounted wings consistently featured unburst LEVs, whereas desiccated wings (measured to be roughly twice the stiffness) created burst LEVs, suggesting that the compliance and flexibility gradient of insect wings contribute to the structure of LEVs. We next measured differences in local angle of attack between fresh and desiccated wings – fresh wings showed a near-linear increase in local angle of attack from root to tip, while desiccated wings featured a near-constant angle of attack outside of a sharp increase across the 40%-60% span region. Bursting occurs near the mid-span point on the wing where this sharp increase in angle of attack was observed. Combined, these results imply that the flexibility distribution of the fresh Manduca wing helps maintain LEV structure.
