Investigations on Flow Characteristics, Surface Loadings and Performances of Vertical Axis Wind Turbine

This study simulates the unsteady flow structures around the small-size vertical axis wind turbines (VAWT) with three straight blades. The software Ansys/Fluent is employed. The effects of collective variations of the blade pitch angle on the surface loadings, the moment coefficients, the self-starting ability and the power coefficient are addressed and discussed. The VAWT system is driven to rotate from rest by the coming wind with a uniform speed 10 m/s, and the pitch angle varies within +/- 10 degrees. The blade profile is NACA 0012. While the pitch angle is positive, the CCW rotation of the VAWT system is primarily provided by an individual blade advancing on the upwind side. On the contrary, at negative pitch angles, the CCW rotation of the VAWT system is provided mainly by the blade advancing on the downwind side. The distributions of moment coefficients, contributed by all three blades, shift toward small p while the pitch angle decreases from theta = 10 degrees to. theta = -10 degrees These trends are in synchronization with those of C-X and C-Y. The primary positive peak value of C-M reaches the maximum at the pitch angle theta = 5 degrees; and the magnitudes are comparable and mostly positive (CCW) within one complete revolution for the case theta = 10 degrees. While the pitch angle decreases from theta = 5 degrees to theta = -10 degrees, the peak magnitude of C-M decreases significantly, the interval (or azimuthal portion) of negative moment extends wider and the negative value of C-M increases within one complete revolution. Within -10 degrees <= theta < 5 degrees, the enlargement of negative C-M, significant reduction of positive C-M and longerinterval (or larger azimuthal portion) of negative values of C-M are the main reason responsible for the retardation of the rotating speed and thus the reduction of the power coefficients of the VAWT system. The self-starting ability is the best at the pitch angle theta = -10 degrees and is degraded monotonously from theta = -10 degrees to theta = 10 degrees.