Abstract
Understanding atmospheric turbulence is without a doubt one of the most complex subjects in meteorology. However, its behavior can be more easily investigated by analysis of high-quality measurements of the velocity and temperature fluctuations. Here, we show that at the large test station of wind turbines in Østerild, northern Denmark, measurements from a 250-m lightning mast provide unique insights into the behavior of atmospheric turbulence within the range of heights where modern large wind turbines operate. We illustrate that for the predominant westerly winds at the site, the flow can be assumed to be close to homogeneous. This allows the analysis of the behavior with atmospheric stability and height of the wind speed and direction and of different turbulence measures, i.a., velocity variances and covariances, as well as turbulence spectra and their characteristics. It is shown, e.g., that for a wide range of atmospheric stability conditions, turbulence parameters up to 241 m are directly related to mean flow characteristics, which will aid in improving the simulation of turbulence in, i.a., aeroelastic simulations. These measurements can be used for the evaluation of a wide range of models describing the meteorological conditions and the atmospheric flow and its turbulent behavior.
Highlights
Boundary-layer meteorology and, for our particular interest, wind-power meteorology rely on flow and meteorological models that can describe the behavior of atmospheric turbulence as accurate as possible
Nowadays almost as robust as cup anemometers, are able to measure all velocity and temperature fluctuations, but due to their measurement configuration, they are affected by self-induced flow distortion
The behavior with the height of the variances follows the same pattern; without accounting for the 7-m level, whose values can be higher or lower than those at 37 m, suggesting that local terrain features highly influence the measurements at the lowest sonic anemometer level, the velocity variances and uw-covariance decrease with the height
Summary
Boundary-layer meteorology and, for our particular interest, wind-power meteorology rely on flow and meteorological models that can describe the behavior of atmospheric turbulence as accurate as possible. Used sonic anemometer and lidar measurements performed in Østerild, prior to the construction of the test station, to investigate the relation between the turbulence length scale and the mean vertical wind shear. The purpose is to introduce the Østerild measurements to boundary-layer and wind-power meteorologists, in particular, those from the sonic anemometers that cover the first 241 m This is mainly done by analysis of the behavior with the atmospheric stability and height of wind speed, direction, velocity variances, covariances, and. For the latter sector, the turbulence spectra and their characteristics with height and atmospheric stability are examined in Sec. VI C 3. The last section provides some perspectives for future work and conclusions
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