Nature’s Wind Turbines: The Measured Aerodynamic Efficiency of Spinning Seeds Approaches Theoretical Limits

Abstract

This paper describe a procedure to measure experimentally the power coefficient, (Formula presented.), of winged seeds, and apply this technique to seeds from the Norway maple (Acer platanoides). We measure (Formula presented.) at a tip speed ratio of (Formula presented.). Our results are in agreement with previously published CFD simulations that indicate that these seeds—operating in low-Reynolds number conditions—approach the Betz limit ( (Formula presented.) ) the maximum possible efficiency for a wind turbine. In addition, this result is not consistent with the recent theoretical work of Okulov & Sørensen, which suggests that a single-bladed turbine with a tip-speed ratio of 3.2 can achieve a power efficiency of no more than 30%.