Wind Tunnel Experimental Study of the Effects of Blade Number on the Performance and Starting Behavior of a Low Tip-Speed Ratio and Micro-Scale Wind Turbine at Fixed Blade Geometry

Abstract

Abstract The effects of the number of blades on the efficiency and starting behavior of low tip-speed ratio micro-scale wind turbines are controversial. In contrast to modern 3-bladed fast large-scale horizontal axis wind turbines, these runners are multi-bladed to increase torque and to perform efficiently in low wind speed conditions. While an optimal number of blades for large-scale wind turbines has been established, it is still under consideration for small wind energy harvesters. The aim of this research is to examine the influence of the number of blades, while maintaining a constant blade chord length, on the power and torque coefficients of micro-scale wind turbines that are specifically designed to work at low tip-speed ratio. Seven 200 mm high-solidity wind turbines with a number of blades varying from 4 to 16 were designed, manufactured, and tested in a wind tunnel to collect the full power and torque coefficients vs. tip-speed ratio characteristics. We found that turbines with a large number of blades are more efficient in low wind speed conditions and have a lower cut-in wind speed than turbines with fewer blades. The experimental results emphasize the existence of an optimal range of blade numbers for our specific blade geometry, between 12 and 14 blades, that decreases the cut-in wind speed while maximizing the power coefficient. Furthermore, we observed that the performance curves of the wind turbines change as the number of blades increases, emphasizing the existence of blade interactions that alter blade aerodynamic properties. In addition, this experimental study provides some guidelines for the development of efficient micro wind energy harvesters.