The Effect of Butterfly Inspired Scales on Wing Tip Vortex Development

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University of Alabama Libraries

Scientists look to nature for bio-inspired aerodynamic efficiency solutions, focusing on insects such as the Monarch butterfly (Danaus Plexippus) since it performs the longest known butterfly flight migration. This experiment focuses on the scale patterning found on the wing tips, where scales are three times the size of the traditional scales that coat the wing surface. It was hypothesized that the long wing tip scales of the Monarch butterfly act to modify the growth and development of the tip vortex in order to enhance flight conditions and influence the stability of the LEV. It is well documented that a stronger tip vortex acts to anchor the LEV, delaying separation. An experiment was conducted focusing on the alteration of vortex development using a tip geometry representative of the Monarch butterfly wing tip scales. Two models were developed, a flat plate baseline case and a scale plate model where the LE of the plate was lined with a singular row of 3D printed, butterfly inspired scales. The LEVs generated by both plates were compared in an experiment where the plate translated vertically through a tow tank filled with mineral oil, resembling a viscosity similar to air. The plate was tested using DPIV at 90 and 45 degree angles and flow fields at Re = 9, 36, and 47. The Re = 47 case most closely represented the flight conditions of the butterfly during flapping flight. Flow fields from each of the twelve cases point to the development of a wing tip vortex, which varied for each Re examined. In each case, the U Velocity, vorticity, and circulation were examined using Tecplot and Matlab. Ultimately, the addition of tip scales increased the strength of the vortex compared to the flat plate model, increasing vorticity and therefore lift, but unexpectedly also initiating a faster vortex separation, pointing to an aerodynamic advantage from the addition of wing tip scales.

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