Aerodynamic performance and flow structure investigation of contra-rotating wind turbines by CFD and experimental methods

Wind tunnel experiment was carried out to measure mechanical power of the contra-rotating wind turbine (CRWT) and single rotor wind turbine (SRWT) under various working conditions. Particle Image Velocimetry (PIV) device was employed to measure the transient flow field on the meridional plane of the rotors. The azimuthal velocity vector, magnitude and streamline were obtained by the average PIV image of ten intervals in a rotation cycle. CFD model of steady flow was developed to predict aerodynamic performance and flow structure of the CRWTs using S-A turbulent model. The single channel model was employed with periodic boundary condition. CFD results were validated with wind tunnel test in literature and experiment in this paper. Results show that CFD method has a satisfied accuracy in power prediction, with a relative error less than 34%. The azimuthal average velocity distributions predicted by experimental and CFD methods are close and the maximum value are approximate to each other. Results demonstrate a high velocity zone at the outside of the front rotor tip and a low velocity zone near the middle of the rear rotor. CRWT has a complicated flow structure. Particularly at the rear rotor, flow becomes uneven and streamline curvatures are more ununiformed.