Meeting Abstract

P3.144  Friday, Jan. 6  Dynamic Drag of Broad Leaves and Physical Models in Strong Wind JONES, S.K.*; MILLER, L.A.; HEDRICK, T.L.; Univ. of North Carolina, Chapel Hill; Univ. of North Carolina, Chapel Hill; Univ. of North Carolina, Chapel Hill

Leaves reconfigure into cone shapes that reduce drag in strong wind and moving water, compared to rigid objects of similar surface area. The flexibility of the leaves allows for reconfiguration, which is responsible for the reduction in drag. However, flexibility and reconfiguration are themselves insufficient to produce a reduction in drag; objects such as flags experience greater drag than equal area flat plates. Thus, it is not clear how flexible leaves reconfigure into stable shapes with reduced flutter and oscillations. Here, the dynamic drag experienced by tulip poplar, Liriodendron tulipifera, leaves in wind are compared to physical models of flexible sheets attached to petiole-like flexible beams. Leaves and physical models are attached to a cantilever beam equipped with strain gauges to measure dynamic drag over a range of wind speeds in a wind tunnel. Flutter and oscillation frequencies are analyzed by inspecting the power spectrum of the drag signal. Average drag, peak drag and frequency of oscillation are compared in leaves and physical models. Flexible rectangular models that reconfigure into U-shapes experience larger peak forces and oscillation compared to models that reconfigure into a cone-shape. These results suggest that the three-dimensional cone shape adopted by leaves, in addition to flexibility, is important to reducing forces.