Study on approach of performance improvement of VAWT employing double multiple stream tubes model

On the circular blade path of a Darrieus-type vertical axis wind turbine (VAWT), there are two azimuth positions where torques are small or even negative. These two azimuths have the lowest aerodynamic performance and greatly weaken the overall performance of the VAWT. An approach is proposed to rebuild the flow field of the turbine blades by applying two additional airflows at the two azimuths to enhance the local performance. The aim is to improve the overall power coefficient of the VAWT. A Φ-type VAWT with a diameter of 2 m and a height of 2 m is studied to evaluate the effectiveness of the proposed approach. The effect of additional airflow on the aerodynamic performance of the blade and the turbine is researched using the double multiple streamtube model. The simulation results suggest that the additional airflows are effective in promoting the performance of the rotor blades and the overall rotor; the increase in maximum power coefficient achieved was 6% at an optimum tip speed ratio. Some rules of the effect on the performances of the rotor are obtained in this paper.