Experimental Investigations on Sail Type Wind-Turbines

Abstract

Horizontal and vertical axis type wind turbines using sails (instead of rigid blades) are experimentally investigated. Cretan type wind turbines are horizontal axis sail type wind turbines. The simple design, low cost and ease of construction of these turbines make them an attractive option for areas having low wind velocities. Coefficient of power and coefficient of torque for Cretan type rotor with 5 blades for a solidity ratio of 0.85 is studied. The type of the cloth used is polyester with porosity ranging between 75 to 300 μm. Experiments are conducted for Reynolds number of 1 × 105 and 1.2 × 105 and tip speed ratios ranging between 0 and 0.1. Influence of sail angle (5°, 15°, 25° and 30°) on the performance of the horizontal axis sail type wind turbines is investigated. Sail angle of 25° gives the maximum coefficient of power of 0.31 at a tip speed ratio of 0.71. Sail Savonius wind turbines are investigated on the vertical wind turbine domain. The enhanced performance of Cretan type wind rotors using sails laid the foundation for studying the behavior of Savonius wind turbines with flexible blades. The sail Savonius rotor used in the study has a rotor diameter of 180 mm with an overlap ratio of 0.15. The type of cloth used is polyester with the porosity ranging between 75 to 300 μm. The performance characteristic curves are measured for Reynolds number of 9 × 104 and 1 × 105. The peak value of coefficient of power is around 0.05 at a tip speed ratio of 0.43 for a Reynolds number of 1 × 105.