Measurement of rotor centre flow direction and turbulence in wind farm environment

The measurement of inflow to a wind turbine rotor was made with a spinner anemometer on a 2 MW wind turbine in a wind farm of eight wind turbines. The wind speed, yaw misalignment and flow inclination angle was measured during a five months measurement campaign. Angular measurements were calibrated by yawing the wind turbine in and out of the wind in stopped conditions. Wind speed was calibrated relative to a met mast in a wake-free wind sector during operation. The calibration measurements were used to determine the basic k1 and k2 constants of the spinner anemometer and a four parameter induction factor function. Yaw measurements and turbulence measurements, where the average wind speed was corrected to the far field with the induction function, showed good correlation with mast measurements. The yaw misalignment measurements showed a significant yaw misalignment for most of the wind speed range, and also a minor symmetric yaw misalignment pattern. The flow inclination angle showed slight variation of inflow angle with wind speed and clear wake swirl patterns in the wakes of the other wind turbines. Turbulence intensity measurements showed clear variations from low turbulence in the wake-free wind sector to high turbulence in the wakes of the other wind turbines.