Kinematic responses of an autorotating samara to concentrated crosswind

• Published in: Physics of fluids (1994) 2022-11, Vol.34 (11)
• Main Authors: Atkins, Michael D., Kim, Tongbeum
• Format: Article
• Language: English
• Subjects: Autorotation; Crosswinds; Descent trajectories; Dispersion; Kinematics; Modal response; Velocity; Wind effects
• ISSN: 1070-6631; 1089-7666
• DOI: 10.1063/5.0125421

A single-winged maple seed (samara) is dispersed laterally by a crosswind in contrast to simply descending straight down (zero dispersion) in quiescent air. This article presents the general kinematic response of a particular type of samaras (Acer buergerianum) in stable autorotation to the disturbance of a concentrated crosswind (simulated via slot jet) with the crosswind strength varied distinctively from weak to strong. A relatively weak crosswind slower than the tip velocity of the stably autorotating samara causes only damped undulations of its descent trajectory. In contrast, we demonstrate that the samara exhibits a bi-modal response when disturbed by a relatively strong crosswind (velocity greater than samara tip velocity). The strong crosswind enables the samara either to float laterally with the crosswind or drop-out through the crosswind with the switching of its rotational direction. Regardless of crosswind strength, stable autorotation is re-established after the samara leaves the crosswind zone, albeit accompanied by large-scale undulations in its descent trajectory. More importantly, before landing, the samara regains its original terminal descent velocity achieved in quiescent air.