Extending the operating limits and performances of centimetre-scale wind turbines through biomimicry

Abstract

This paper reports the design and fabrication of an innovative small-size propeller and its experimental testing once assembled with an electromagnetic generator. The bioinspired rotor is based on the shape and behaviour of maple samaras that optimise the aerodynamics at low Reynolds numbers. To the authors’ knowledge, it is the first samara-based wind energy harvester reported to date and one of the smallest wind turbines in the literature. The different blade angles and the number of propeller blades are optimised. A permanent magnet miniature generator with low friction ceramic bearings is used to convert rotation into electrical power. The performance of this 44 mm diameter horizontal-axis wind turbine is tested under wind speeds from 1.2 to 8 m s−1. The output electrical power measured in resistive load is between 41 μW and 81.7 mW, which leads to an overall efficiency between 2.6 (1.2 m s−1) and 17.8% (4 m s−1). Estimates of different losses in the harvester make it possible to determine power coefficient CP which reaches 28.4%. Among the miniature wind turbines in the literature, this device demonstrates one of the highest rates in terms of efficiency and power density. Moreover, thanks to its operating speed decreased to 1.2 m s−1 – the lowest in the state of the art – it presents one of the largest ranges of airspeeds for energy harvesting.