Wind induced deformation and vibration of a Platanus acerifolia leaf

Abstract

Deformation and vibration of twig-connected single leaf in wind is investigated experimentally. Results show that the Reynolds number based on wind speed and length of leaf blade is a key parameter to the aerodynamic problem. In case the front surface facing the wind and with an increase of Reynolds number, the leaf experiences static deformation, large amplitude and low frequency sway, reconfiguration to delta wing shape, flapping of tips, high frequency vibration of whole leaf blade, recovery of delta wing shape, and twig-leaf coupling vibration. Abrupt changes from one state to another occur at critical Reynolds numbers. In case the back surface facing the wind, the large amplitude and low frequency sway does not occur, the recovered delta wing shape is replaced by a conic shape, and the critical Reynolds numbers of vibrations are higher than the ones corresponding to the case with the front surface facing the wind. A pair of ram-horn vortex is observed behind the delta wing shaped leaf. A single vortex is found downstream of the conic shaped leaf. A lift is induced by the vortex, and this lift helps leaf to adjust position and posture, stabilize blade distortion and reduce drag and vibration.

Morphological Response of Eight Quercus Species to Simulated Wind Load

“…Leaves tend to be vibrated, deformed and reconfigured under wind load [ 21 – 22 ]. The shape of the leaf, such as leaf size, leaf dissection index (LDI), and venation distribution, could regulate momentum forces on leaves and woody portions as a whole on the canopy.…”

Flapping dynamics of an inverted flag

“…An inverted pendulum under gravitational force and a buckling bar under compressive force are such examples. The vibrating leaves of a tree also give a hint for this inverted flag design (Shao, Chen & Lin 2012). The leaves can flutter in a breeze regardless of their orientation to wind, which exemplifies that the flag-type configuration is not a necessary condition for flow-induced flapping.…”

Swaying Tree Simulation by Slicing Partition

“…Additionally, leaves shaking, including the bending and rotating [17] , is also a complex and important role in a dynamic tree, but only a few methods [3,4,7] considered it. Since the leaves are not smooth, the wind is usually diffused while touching on them.…”

“…In contrast to branches, leaves are not smooth so that the wind will be diffused when touching on them, leading to the acted stresses are not uneven. Apart from the bending that has been widely researched, therefore, leaves will rotate about their petioles in the vibration of wind [17] . To reduce the computational complexity with satisfactory visual requirements, we add a diffuse stress factor ξ to acting wind for approximating the diffusion.…”