Design and performance of a small shrouded cretan windwheel

Abstract

A Cretan-type windwheel is attractive because of its design simplicity, low cost, durability and ease of construction by semi-skilled labour from a variety of indigenous materials. Utilising a 0·64 m diameter cycle wheel as the structurally strong framework for the windwheel sails provides a rotor that is sufficiently rigid, relatively cheap (especially if the wheel and axle are cannibalised from an abandoned bicycle) and readily available throughout the world. Sail manufacture, assembly and maintenance for a Cretan windwheel can usually be undertaken locally, so eliminating the high costs of importing commercially available wind energy conversion systems. Thus, Cretan-type windwheels are likely to be increasingly used in less developed countries despite their intrinsically poor capabilities for harnessing wind power. Test data for a shrouded version of the ‘cycle wheel’, Cretan system are presented. The use of nine loosely sheeted sails produced a maximum power output of 14 W for an air speed at entry to the rotor of 5 m s −1, corresponding to a free stream wind of less than 3·5 m s −1. For this system it was found that tight (rather than loose) sails harnessed relatively little power. The presence of the shroud, which reduced tip losses, led to higher power coefficients being attainable. Two possible applications for a larger version (than tested) shrouded, Cretan type windwheel are described, namely (i) for irrigation and land drainage in undeveloped countries and (ii) for stimulating a peristaltic pump which acts as a gravitational boost to drive solar-heated anti-freeze liquid around a low height, domestic central-heating circuit.