"Reconfiguring it out: how flexible structures interact with fluid flows

Mrudhula Baskaran, Ecole polytéchnique fédérale de Lausanne
Louis Hutin, Ecole polytéchnique fédérale de Lausanne
Karen Mulleners, Ecole polytéchnique fédérale de Lausanne

DOI: https://doi.org/10.1103/APS.DFD.2022.GFM.V0070

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.

Music: 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. For educational use only.

See other videos from the 2021 Gallery of Fluid Motion: https://gfm.aps.org/"