  The present investigation provides the first field characterization of the
influence of turbulent inflow on the blade structural response of a
utility-scale wind turbine (2.5MW), using the unique facility available at the
Eolos Wind Energy Research Station of the University of Minnesota. A
representative one-hour dataset under a stable atmosphere is selected for the
characterization, including the inflow turbulent data measured from the
meteorological tower, high-resolution blade strain measurement at different
circumferential and radiation positions along the blade, and the wind turbine
operational conditions. The results indicate that the turbulent inflow
modulates the turbine blade structural response in three representative
frequency ranges: a lower frequency range (corresponding to modulations due to
large eddies in the atmosphere), a higher frequency range (corresponding to
flow structures in scales smaller than the rotor diameter), and an
intermediate-range in between. The blade structure responds strongly to the
turbulent inflow in the lower and intermediate ranges, while it is primarily
dominated by the rotation effect and other high-frequency characteristics of
wind turbines in the higher frequency range. Moreover, the blade structural
behaviors at different azimuth angles, circumferential and radial locations
along the blade are also compared, suggesting the comparatively high
possibility of structural failure at certain positions. Further, the present
study also uncovers the linkage between the turbulent inflow and blade
structural response using temporal correlation. The derived findings provide
insights into the development of advanced control strategies or blade design to
mitigate the structural impact and increase blade longevity for the safer and
more efficient operation of large-scale wind turbines.
