University of Alabama, Tuscaloosa, USA
Date(s) : 09/02/2022 iCal
16 h 00 min - 17 h 00 min
Sharks and butterflies swim and fly in different flow regimes, yet the structure of their surfaces interacting with the surrounding fluid appear to both contain very important microscopic features that lead to reduced drag and increased flying or swimming efficiency. Sharks have moveable scales (on the order of 200 microns in size) that have been demonstrated to act as a passive, flow-actuated dynamic roughness for separation control. Water tunnel experiments with real shortfin mako shark skin samples mounted to models have shown significant control of flow separation in both laminar and turbulent boundary layer scenarios. Alternatively, butterfly scales (100 microns in size covering the wings in a roof shingle pattern) appear to fundamentally alter the local skin friction drag depending on flow orientation for what is dominantly a laminar boundary layer interacting with the wings. However, in this case the surface may also slow the growth and formation of the leading-edge vortex and these effects shown in experiments may help explain a mean decrease in climbing efficiency (joules per flap) of 32.2% for live butterflies once their scales were removed. An overview of these results will be presented bringing out the importance of finding solutions in nature for important engineering problems.