The airfoils for the horizontal axis wind turbine operated in the wide attack angle range with dynamic change due to the wind speed variation and yaw miss alignment. These attack angle changes are large in the inboard part of the rotor blade.However most of airfoils are evaluated by the wind tunnel test or the CFD calculations in the static state where the attack angle is fixed. In this study, the dynamic state performances of the airfoils are evaluated by the wind tunnel measurements. The pressure distribution measurements in the dynamic state are performed for three kinds of airfoil. The airfoil performances for both static and dynamic state are shown and the relation between both states are discussed. The hysteresis loop in lift coefficient to attack angle curve depends on the maximum value of attack angle variation. The stall characteristics for the dynamic state depend on the static stall characteristics.
The author made a dynamical formula by use of a simple model which unites the torque by wind in reaction type wind turbine and the torque by electric generator. The formula shows that an output power is optimized by circuit resistance R, inverse electromotive force voltage coefficient of generator KE and radius of wind turbine r0 and the optimization is simply represented by a factor X=KE2/Rr02. This formula makes it possible to estimate the output power optimization quantitatively. The comparison with the experimental data showed the validity of this theoretical formula.