A field experiment was carried out to study the unsteady behavior of an instrumented full-scale 2.5 MW wind turbine under neutral conditions. The analysis focused on the structure of the instantaneous turbine power and strain at its foundation. A meteorological tower located 1.6 rotor diameters upstream of the turbine was used to characterize the turbulent flow. Mean velocity and temperature were steady during the 1 h period selected. The results suggest that the turbine power and foundation strain are modulated by atmospheric turbulence in a complex way. The spectral characteristics of both quantities exhibited three distinctive regions. Within the first region, defined by subrotor length scales, the turbine power was insensitive to the flow turbulence. In the intermediate region, with length scales up to those on the order of the atmospheric boundary layer thickness, the spectral contents of the power fluctuations ΦP and flow ΦU exhibit a non-linear relationship of the form ΦP = G(f)ΦU, where G(f) ∝ (∼) f-2 is a transfer/damping function. In the third region, dominated by the very large scales of motions, the power fluctuations are found to be directly influenced by the flow. The strain also showed three regions, similar to the power fluctuations. However, it follows the structure of the inertial subrange of the turbulence at subrotor scales. Intermittent gusts were able to induce intermittent behavior on the turbine power. Finally, the flow and power correlation showed that the velocity at the hub height is the best descriptor of the flow turbulence within the rotor area.
Bibliographical notePublisher Copyright:
Copyright © 2014 John Wiley & Sons, Ltd.
- Atmospheric boundary layer
- Field experiment
- Power fluctuations
- Turbine loading
- Wind energy
- Wind turbine