Plants harness their flexibility to withstand high fluid forces during heavy winds and extreme weather events. They reduce the drag force they experience by streamlining themselves in the incoming flow. We study the influence of flexibility on the drag that is generated using an elegant geometry: plastic disks that bend symmetrically. This video showcases experiments where disks are pulled through water at different velocities. The disks reconfigure, or bend, more when they are travelling faster. Highly flexible disks also reconfigure more than rigid disks. The fundamental parameter that controls disk reconfiguration is the Cauchy number. This is the ratio between the fluid’s inertia and the elastic restoring force of the disk, which resists bending. We visualize the elegant flow structure that forms behind a moving disk: an axis-symmetric vortex ring. By manipulating the disk’s flexibility and the flow velocity, we directly manipulate the vortex ring and the drag force. Our research has potential in better designing flexible objects which can endure high velocity flows, such as aircraft wings, parachutes, or even buildings.
Audio:
Composer: Franz Liszt
Composition: Etude 3 - Un sospiro in D flat major
Performer: Ida Cernecka
Artist: Dubravka Tomsic
Licenses of music source: INgrooves (on behalf of Denon) and 1 Music Rights Societies
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