PARAMETERISATION OF TURBULENCE INTENSITY

摘要

The design fatigue loading of wind turbine structure is usually determined from aeroelastic simulations, where a structural dynamic model is exposed to suitable synthetic turbulence fields. In the IEC 61400-1 standard, the (design) turbulence intensity, characterising the wind field, is a constant whose value depends on the selected turbulence category. However, in full-scale measurements the turbulence intensity is a stochastic quantity that need to be described by a suitable probability density function. In the present analysis, which is based on a huge number of wind speed time series extracted from "Database on Wind Characteristics" (http://www.winddata.com/), (conditional) Log Normal distribution parameters are estimated that characterises the turbulence intensity as function of wind speed at different heights and locations. Usually measured time series data is de-trended to eliminate the contributions from long-term changes and the influence/effect of this de-trending process on the estimated distribution parameters is investigated for different locations. Finally, the quantiles in the estimated turbulence intensity distributions, corresponding to the specified design turbulence intensities in the IEC 61400-1 standard, are determined and assessed by means of a simple heuristic load model. The IEC recommended turbulence intensity corresponds to the conservative design turbulence intensity at wind speeds below 15 m/s, while IEC values seems to be more concervative for wind speeds above 15 m/s.