Windblown Leafs: Drag Reduction Through Shape Reconstruction in Thin Foldable Plates

The physical mechanism of drag reduction through shape reconstruction in a flow field has been extensively studied in geometries primarily modeled as bending deformable plates and beams. Leaves, consisting mainly of blades and veins, represent a typical thin-walled structure, where the thin-walled nature of the veins can result in significant deformation under fluid loading. Unlike rigid structures, leaves in a flow field can achieve drag reduction through shape reconstruction, thereby resisting damage. The deformation of leaves reduces the drag acting on their structure until the fluid loading reaches an upper limit and no longer increases with flow speed. Additionally, the presence of hinge-like structures on thin sheets results in varying degrees of bending along specific degrees of freedom. We observe a development trend in the study of passive deformation of flexible bodies: from simple two-dimensional flexible fiber deformation to three-dimensional flexible thin plate deformation; from deformation of plates with uniform stiffness to those with non-uniform stiffness distribution. The idea of pre-setting creases on thin plates is inspired by the veins of leaves. This controllable deformation mode concentrates motion along the creases, functioning like hinges around which the surfaces rotate. The crease pattern provides conditions for three-dimensional deformation, allowing shape changes along specific folding paths. Inspired by this, we explore the fluid-flexible body coupling process of this flexible thin plate deformation and verify numerical simulation results in wind tunnel experiments. We conduct studies on shape reconstruction and drag characteristics of flexible thin plates with different stiffness and geometries in wind fields, investigating the mechanisms of shape reconstruction, principles of drag reduction, and the influence of vein distribution on the drag reduction effect.