Abstract:
The authors have developed a simplified curved-plate blade of high power coefficient for small wind turbine
depending on the design concept of the “Appropriate Technology (AT)”. In this study, the shapes of blade are the
tapered type, the straight type and the inversely tapered type and the diameter of all experimental model is 600[mm],
number of blades is 5, thickness of plate is 2[mm]. The bent angles of these three types of the blades are 10, 20 and
30[deg] respectively. Blades pitch angle 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 to rotational
speed was measured by 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. In these result,
the maximum power coefficient for tapered type is Cpmax=0.278 when bent angle is 30[deg] and blade pitch angle
is 10[deg]. Thus, straight type is Cpmax=0.303 when bent angle is 30[deg] and blade pitch angle is 15[deg]. And
inversely tapered type is Cpmax=0.338 when bent angle is 30[deg] and blade pitch angle is 15[deg]. The most efficient
model was inversely tapered type. Moreover, to clarify the details of air flow around the each rotor for the maximum
power coefficient, the authors conducted through visualization test using the smoke oil, high-speed camera and
vector analysis using the P.I.V. system. From the visualization test and P.I.V. analysis, it was clarified that the wind
speed of inflow around tip of tapered type is about 7.5[m/s], on the other hand, inversely tapered type is about
8.0[m/s]. From these results, it could presume that the latter type is more effectively converting the air flow into the
shaft power than that of the former type.
