Turbulence Descriptors for Scaling Fatigue Loading Spectra of Wind Turbine Structural Components

The challenge for the designer in developing a new wind turbine is to incorporate sufficient strength in its components to safely achieve a 20- or 30-year service life. To accomplish this, the designer must understand the load and stress distributions (in a statistical sense at least) that the turbine is likely to encounter during its operating life. Sources of loads found in the normal operatingenvironment include start/stop cycles, emergency shutdowns, the turbulence environment associated with the specific site and turbine location, and extreme or 'rare' events that can challenge the turbine short-term survivability. Extreme events can result from an operational problem or violent atmospheric phenomena. For the majority of the operating time, however, the character of the turbulentinflow is the dominant source of the alternating stress distributions experienced by the structural components. Methods of characterizing or scaling the severity of the loading spectra (or the rate of fatigue damage accumulation) must be applicable to a wide range of turbulent inflow environments--from solitary isolation to the complex flows associated with multi-row wind farms. The metricschosen must be related to the properties of the turbulent inflow and independent of the nature of local terrain features.