Reconfiguring it out: how flexible structures withstand high fluid forces*

Plants and other flexible structures reduce the drag they experience when subject to high velocity flows. Plants streamline their bodies and reduce their projected area to the flow, in a process known as reconfiguration. The drag reduction results from changes in the topology of the vortex ring that forms behind the reconfiguring object. Here, we study the evolution of the vortex ring and its effects on the transient drag force behind flexible disks. Radial incisions are made to the disks to allow them to reconfigure symmetrically without buckling. We quantify the reduction in the projected area of the disks from deformation measurements and analyse the vortical structures behind the disks using time-resolved particle image velocimetry. We relate these quantities to the transient drag force measured with a high-resolution load cell. We also provide a prediction of the drag coefficient for disks with different flexibilities based on the projected area and vortex topology. These findings enable us to better understand the behavior of reconfiguring plants and design structures that withstand high fluid loading.