The effective shape of surrounding structures was investigated to improve the power output of vertical axis wind turbines through wind tunnel experiments. A VAWT equipped with a pair of vertical flat plates in the upstream demonstrated power augmentation by a factor of 2.4 compared to the VAWT without plates. The pair of plates could accelerate the gap flow in the downstream wind, and also could reduce a drag force to a blade of a VAWT toward upstream. We proposed a recommended shape of the structures which consist of flat panels in the upstream.

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A new mechanical and passive over-speed control system (OCS) for vertical axis wind turbine (VAWT) has been proposed aiming at the safety improvement and the cost reduction. The OCS slants the blades to make them work as an air brake by using the centrifugal force when the rotor rotational speed increases. When the speed decreases, the system restores the blades to original state by the force of springs. The OCS has a function to synchronize the movements of blades each other. The performance of an aluminum circular-bladed butterfly wind turbine (ACBBWT), which is equipped with the OCS and whose rotor diameter is 3.16m, is predicted by the blade element momentum (BEM) theory and is compared with the experimental results under the condition of no load. The continuous twist action of the blades was observed in the experiments. As the results, the over-speed control under the high wind speed conditions was verified and the validity of theoretical prediction was shown.

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