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

This paper describe a procedure to measure experimentally the power coefficient, C-p, of winged seeds, and apply this technique to seeds from the Norway maple (Acer platanoides). We measure C-p=56.9 +/- 2% at a tip speed ratio of 3.21 +/- 0.06. 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 (C-p=59.3%) the maximum possible efficiency for a wind turbine. In addition, this result is not consistent with the recent theoretical work of Okulov & Sorensen, 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%.

Automated summary

This paper describes a method to experimentally measure the power coefficient, C-p, of winged seeds, and applies this technique to seeds from the Norway maple. The results show that these seeds, operating in low-Reynolds number conditions, approach the Betz limit, which is the maximum possible efficiency for a wind turbine. However, this result contradicts with the recent theoretical work.