Input Turbulence Features at a Megawatt-Size Wind Turbine at Medicine Bow, Wyoming

In response to recent observations that wind turbulence has a strong effect on wind turbine fatigue life, measurements of turbulent wind velocity profiles have been made at the Medicine Bow, Wyo., WTS-4 wind turbine site. These measurements were taken at seven levels spanning the WTS-4 rotor height on a single meteorological tower 1.75 rotor diameters upstream of the turbine. Concurrent measurements of rotor response were also made. Analysis of the winds at the Medicine Bow site reveals the influence of atmospheric and geographic conditions on what may, at first glance, appear to be a “classic, simple, flat terrain” case. The turbulence data are analyzed to (1) characterize the wind in terms of fixed-point, single-tower properties and (2) model the wind properties as they would be experienced by points on rotating turbine blades. The STRS-2 model, developed by the Pacific Northwest Laboratory, is used to convert single-tower wind characteristics into an estimate of those that would be measured from an array of towers arranged in a crosswind line covering the rotor disk. A response function for the flatwise root bending moment of one of the WTS-4 turbine blades is computed using the turbine data and the STRS-2 data. The STRS-2 model provides a substantially improved correlation with wind turbine blade bending moment over other single-tower estimation methods.