Effect of the wind direction on the near wake structures of an Archimedes spiral wind turbine blade

For urban usage of an Archimedes spiral horizontal axis wind turbine, the effect of wind direction was examined for the confront measurement planes from 0A degrees to 15A degrees. Aerodynamic characteristics in the near wake of wind turbine blade were investigated using the particle image velocimetry method. Ensemble and phase-averaged velocity fields were obtained in both front and lee sides of the blade with various angles of attack. The streamlines are parallel with the incoming flow for the range of attack angles; however, wake velocity is decreasing with increasing angle of attack. It has been found that the trajectory of tip vortices varies significantly in the front side plane compared to that of lee side plane when the angle of attack is higher than 10A degrees. Distance between two consecutive vortices in the front plane decreases monotonically with increasing attack angle, while that in the lee side shows an opporsite manner.