Meeting Abstract
14.1 Monday, Jan. 4 Locomotion by flexible foils: effect of length and stiffness on performance BAKER, T.V.*; ANDERSON, E.J.; LIM, J.L.; LAUDER, G.V.; Grove City College; Grove City College; Harvard University; Harvard University bakertv1@gcc.edu
The propulsive and control surfaces of swimming and flying organisms are flexible and variously shaped. These physical characteristics affect how such structures interact with the surrounding fluid, and therefore have an impact on swimming performance. Plastic strips (height = 6.9 cm) of various stiffness and length (l = 0.5 – 30 cm) were flapped in a flume by a robot mounted on air-bearings. This made it possible to measure the self-propelled speed of each strip, which was used as a metric of swimming performance. The strips were mounted in the streamwise direction and actuated at the leading edge in heave only (i.e. the transverse direction). Swimming speeds ranged from 15 to 50 cm s-1 representing Reynolds numbers between 2.6 x 104 and 8.7 x 105. The motion of the flapping strips was captured by high-speed video and digitized. Stiffness and strip length had significant effects on swimming performance. Most interestingly, strips of particular stiffnesses exhibited multiple maxima and minima in self-propelled speed at different lengths, suggesting a mechanism with resonant harmonics. However, the wave forms observed in the strips did not match standing-wave patterns calculated from the strip wave speeds and lengths, assuming even partial reflection of the strip wave. Nevertheless, for a given strip stiffness the average wave amplitude over the entire strip and self-propelled speed rose and fell together as strip length was increased. These findings are evidence of a fluid-structure interaction that is strongly affected by the length and stiffness of the strip. This phenomenon may be an important factor in understanding the functional morphology of flexible propulsors.
