Performance of a cross-flow wind turbine located above windbreak and snow fences and the associated velocity fields have been investigated experimentally. Effects of the nonporous area of the fence, as well as the direction of the turbine rotation were examined. The standard porous board fence model had the geometric shielding rate of 60%. When the turbine was rotating clockwise, i.e. the blades on the upstream side of the turbine were moving upward, the maximum power coefficient increased with the increasing the nonporous area of the fence. In contrast, when the turbine was rotating counterclockwise and the small clearance between the turbine and the fence, the maximum power coefficient decreased rapidly with the increasing the nonporous area of the upper part of fence. It was found that the power of wind turbine was related to the flow velocity in the clearance region and the rotational direction of the wind turbine.

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An aluminium circular-blade butterfly wind turbine (ACBBWT) was developed (diameter: 2.06 m). Four aluminium circular blades were extruded and bent to shape, then attached directly to a rotating flange. Despite the limitations of uniform blade sections and high weight, easier strength calculations and manufacture enable reduced blade cost compared with fiber-reinforced plastics. Outdoor experiments were conducted with an axial blower (diameter: 3 m), and confirmed the ACBBWT self-starting performance at wind speeds of about 3 m/s. Blade element momentum (BEM) predictions showed that the test turbine should generate about 330 W at low rotational speeds (255 rpm) and wind speed of 12 m/s with an appropriate generator and control system. A 5-blade ACBBWT (diameter: 7.5 m) was simulated by BEM; performance was compared with that of two different rotor-shaped triangular-blade butterfly turbines. The predicted maximum efficiency of the ACBBWT almost equaled that of a triangular-blade rotor of the same diameter.

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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”. In this study, the shapes of the 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 the aluminum 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 were measured by increasing the load gradually. 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. From these results, the maximum power coefficient for the tapered type is Cpmax=0.278 when bent angle is 30[deg] and blade pitch angle is 10[deg]. Then, the straight type is Cpmax=0.303 when bent angle is 30[deg] and blade pitch angle is 15[deg]. And the inversely tapered type is Cpmax=0.338 when bent angle is 30[deg] and blade pitch angle is 15[deg]. Thus the most efficient model was the inversely tapered type. In addition to clarify the behavior of air flow around the each rotor at the maximum power coefficient, the visualization test was conducted using the smoke oil, high-speed camera and vector analysis with the PIV system. From the visualization test and PIV 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.

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