Abstract:

Large eddy simulation of 100 W wind turbine designed by ourselves is carried out in order to analyze and better understand the wake characteristic, such as time-average streamwise velocity, turbulence intensity and structures of vorticity, in shear and uniform inflow. In order to calculate the root-mean-squares of the streamwise velocity and the turbulence intensity, 600 data samples, such as instantaneous velocities and pressure inx, y andz direction, are taken over the last five rotations of the wind turbine blades. The results show that the tip vortex, the center vortex and the streamwise velocity are basically symmetrical without wind shear. When there is wind shear, the pitch of the tip vortex in the top is bigger than the pitch in bottom of the rotor disk, and the center vortex and the streamwise velocity are asymmetrical, and vortexes spread father. Regardless of wind shear, wind-turbine wake expansion phenomenon is not obvious at the y/d<6. Under the condition of same inflow turbulence intensity, the changes of wakes turbulence intensity are similar with and without wind shear. In other words, wind shear has less effect on the wake turbulence intensity.

Key words: the time-averaged streamwise velocity, turbulence intensity, vortex structure, wind-turbine wake, wind shear