Samara-Seed Aerodynamics

Date
2015-01-26
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Abstract
Samaras are tree seeds that spontaneously rotate about the vertical axis as they fall. This flight pattern, referred to as autorotation, generates aerodynamic lift to slow a samara’s descent. In this thesis, samara flight is studied in steady-state and during a transient gust-response. In steady-state autorotation, the circulation and topology of the flow over samaras are investigated using particle image velocimetry (PIV). The stable attachment of leading-edge vortices - a lift-enhancing mechanism - is shown to depend on tip speed ratio. Leading-edge circulation, however, is insensitive to changes in tip speed ratio. The dynamic gust-response of samaras is studied using high-speed video. A linear dynamic model is developed based on momentum theory, and is shown to adequately predict the post-gust acceleration of an Acer negundo samara. The model predicts that axial gusts of sufficient strength or frequency can disrupt autorotation by compromising pitch-stability.
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Keywords
Ecology, Fluid and Plasma, Engineering--Mechanical
Citation
Limacher, E. (2015). Samara-Seed Aerodynamics (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/27706