Meeting Abstract
Butterfly scales, measuring about 0.1mm in size, cover the wing in a roof shingle pattern and present a means by which the skin friction drag may be altered based on flow orientation over the surface. By strategic placement of the scales on the wing it is hypothesized that an aerodynamic benefit may result. This study carried out an experimental investigation of this effect through flight tests of live Monarch butterflies, as well as simplified fluid dynamic studies on leading edge vortex (LEV) formation. The LEV is the main mechanism for lift production during flapping flight. First, a method was developed to measure butterfly flapping kinematics optically over long uninhibited flight. Using the Autonomous Tracking and Optical Measurement (ATOM) Laboratory located at the University of Alabama Huntsville, 22 Vicon cameras were located at the top of a 5.7m × 9.1m × 3.0m capture volume. This permitted millimeter level tracking of reflective markers placed on freely flying specimens. Results for 11 butterflies (246 flights) both with and without their wing scales showed that the mean climbing efficiency decreased by 37.8% after scales were removed. Also, the flapping amplitude decreased by 6.7% while the flapping frequency was not altered significantly. Next, to better understand the effect the scales may have on flight, their effect on LEV development needs to be understood. Experiments carried out using Digital Particle Image Velocimetry found that altering the fluid friction through butterfly-inspired surface roughness had an effect on vortex growth. The potential impact of this result on induced drag and ultimately flight efficiency for a butterfly will be discussed.
