Meeting Abstract

49.1  Thursday, Jan. 6  Rolling up with the flow to reduce drag and flutter: A study of broad leaves MILLER, Laura*; HAMLET, Christina; SANTHANAKRISHNAN, Arvind; University of North Carolina, Chapel Hill; University of North Carolina, Chapel Hill lam9@email.unc.edu

Flexible plants, fungi, and sessile animals reconfigure in wind and water to reduce the drag forces acting upon them. In strong winds and floodwaters, leaves roll up into cone shapes that reduce drag compared to rigid objects of similar surface area. Less understood is how a leaf attached to a flexible petiole (leafstalk) will roll-up stably in an unsteady flow. A combination of experiments and numerical simulations is used to describe the unsteady forces acting upon flexible sheets attached to flexible beams. The results from the simplified physical and mathematical models are then compared to measurements taken from broad leaves. The flexible models oscillate in steady and unsteady flow, and average drag forces are higher than those previously reported for flexible beams and sheets tethered to a rigid point. One important distinction between these models and the actual leaves is the ability to roll up into three-dimensional cone shapes. The experiments were repeated for flexible disks cut along a radius rather than rectangular sheets. These disks reconfigured into stable cone shapes similar to leaves. The wakes behind the models and leaves were measured using particle image velocimetry. The structures that reconfigure into cone shapes show a stable pair of vortices that form within the cone.