Abstract: When the blade of vertical axis wind turbine (VAWT) rotates along a circle, the angle of attack (AOA) versus azimuth follows the curve of sine function approximately. The oscillating AOA results in the waved torque. The traditional variable pitch technologies mainly focus on the performance promotion at the position with higher AOA. The smaller AOA the azimuth has, the smaller pitch angle is designed, and the smaller enhancement is obtained. A new variable pitch strategy is proposed:the smaller pitch angle is employed in the azimuth with higher AOA, while the bigger pitch angle is employed in the azimuth with lower AOA, and the new technology mainly focuses on improvement of aerodynamic performance of azimuth position with small angle of attack. A two-bladed H-type VAWT, employing NACA0012 airfoil and with height 2 m and rotation diameter 2 m, is chosen as research objective. Based on double multiple stream-tubes model, the variation rules of angle of attack, tangential force coefficient, torque and power coefficient are analyzed at the condition of tip speed ratios are 4.5 and 5. The results show that:the new pitch strategy effectively improves AOA, tangential force coefficient, torque and rotor power coefficient. The maximum power coefficient is increased by 18.9% at the tip speed ratio of 5. The zones of higher performance are amplified and the zones owned lower performance get narrowed. The computation results have good agreement with experiment results and the ones of reference, which proves that the results of the paper own high accuracy and credibility.

Key words: aerodynamic performance, double multiple stream tubes mode, H-type VAWT, pitch strategy