Uncertainties in offshore wind turbulence intensity

Abstract

In the development, design and operation of wind farms the knowledge of wind turbulence intensity is of paramount importance, particularly at hub height. Given that measurements are rare, turbulence intensities are often determined using simplified formulations. These formulations only account for a dependence on wind speed and include a neutral stability assumption. There are, therefore, large uncertainties associated with the results of such formulations. In order to quantify these uncertainties we determine the dependence of turbulence intensity at different heights on the surface wind velocity, wave conditions and vertical temperature gradients from offshore LiDAR wind observations in the North Sea. The turbulence intensity is shown to depend strongly on the atmospheric stability and less strongly on the sea surface roughness. The lower turbulence intensity values are observed under stable atmospheric conditions. The dependence of the turbulence intensity on the surface roughness is higher at the lower levels, with the significant wave height being the sea surface roughness parameters with the stronger correlation with the turbulence intensity.