Lidar Measurement of Turbulence Encountered by Horizontal-Axis Wind Turbines

Abstract

We used a continuous-wave (CW) Doppler lidar to measure wind velocity turbulence from a moving frame of reference. By directing the lidar beam to trace the perimeters of vertical-plane disks about horizontal axes parallel to the mean wind direction, we observed turbulence properties similar to those encountered by the tips of revolving turbine blades. As in other measurements made with in situ sensors, turbulence spectra observed from the moving reference points showed a decrease in energy, relative to fixed point observations, at frequencies just below the rotation frequency of the lidar beam, and an increase in energy within discrete spectral bands at higher frequencies. Comparisons with a simple model showed reasonable agreement, although measurement conditions did not correspond to the assumptions of the model. On the basis of the results of this experiment, we conclude that Doppler lidar, with appropriate signal processing, is quite applicable for measurement of turbulence encountered by spinning wind turbines.