78th Annual Meeting of the APS Division of Fluid Dynamics (Nov 23 — 25, 2025)

V013: Dancing with the wind, learning from the choreography of flapping leaves

Flexibility is a survival factor in nature: leaves deform to adapt to strong incoming winds, allowing trees to survive heavy storms. In some wind conditions, the deformation of leaves resembles the waving motion of flapping flags. Unlike flags that are mostly rectangular, leaves come in a myriad of shapes. Does the shape of leaves affect their interactions with the wind? And if so, how? To answer these questions, we designed a self-exploring automated experiment using a robotic arm to cut leaf-inspired shapes from paper and measure their time-resolved deformations in a wind tunnel. In the movie, we use the analogy of dance choreographies to describe the different flapping motions. The time-resolved deformation of the leaves was decomposed into characteristic modes, and the flapping motion was represented by a limit cycle oscillation in a low-dimensional phase space spanned by the most dominant flapping mode coefficients. Leaves with different shapes resulted in different limit cycles or loops. We further discretised the loops and characterised the flapping of leaves through the succession of different key sequences, like steps in a dance tutorial. We identify similarities between the 'dance tutorials' that correspond to leaves with similar morphological features. Leaves with similar shapes not only share flapping signatures, but they also yield matching drag values. Furthermore, leaf-inspired shapes experience lower drag values than rectangular flags, suggesting that leaves are ideal dance partners for the wind. *This work was financially supported by the Swiss National Fund (Grant n°200021-232147).*Song: The Age of Wood, Savfk.