Abstract
The research of the optimum wing for the purpose of the performance improvement of straight wing vertical axis wind turbine in the windmill was carried out. In practical Reynolds number region of the windmill, wind tunnel experiment of the NACA system symmetric airfoil of various thicknesses was carried out. The experiment was carried out using the wing with several kinds wing tip, and the method for measuring three components of force at the good accuracy was examined. And, the windmill efficiency was calculated using the measured airfoil performance value. As the result, the effect of airfoil performance on the wind turbine performance was clarified.
