DEVELOPMENT OF A SMALL WIND TURBINE ADOPTING FOLDED-PLATE BLADES -PERFORMANCE OF BLADES WITH ONE AND TWO STRAIGHT FOLDING LINES-

Abstract

The authors have developed a simplified folded-plate blade with high power coefficient for small wind turbine on the design concept of the “Appropriate Technology (AT)”. In this study, the shapes of the blades are the tapered type, the straight type and the inversely tapered type and the diameter of all experimental model is 600[mm], the number of blades is 5, and the thickness of plate is 2[mm]. Each blade has a single folding line. The folding angles for these three types of the blades are 10, 20 and 30[deg] respectively. Blade pitch angles can be changed manually at 0, 5, 10 15, 20 and 25[deg]. In the experiment of all rotors, the wind speed in the wind tunnel is set at 10[m/s] and the torque and the corresponding rotational speed were measured gradually increasing the load. From the results of the experiment, the power coefficient Cp and the tip speed ratio λ were calculated to obtain the power characteristics for different blade types. As a result, the maximum power coefficient for tapered type is Cpmax=0.278 when folded angle is 30[deg] and blade pitch angle is 10[deg]. For the straight type, Cpmax=0.303 when folded angle is 30[deg] and blade pitch angle is 15[deg]. And inversely tapered type is Cpmax=0.337 when folded angle is 30[deg] and blade pitch angle is 15[deg]. The most efficient model was inversely tapered type. Additionally, for the inversely tapered type blades, we examined the performance of them with two straight folding lines whose angles are selected from 5, 10, 15 and 20[deg]. Blade pitch angles are also changed at 0, 5, 10, 15, 20 and 25[deg]. The result shows the maximum power coefficient is 0.372 when two folded lines whose angle are 5[deg], 10[deg] parallel the forward edge with blade pitch angle of 20[deg].