A comparison of fatigue loads of wind turbine resulting from a non-Gaussian turbulence model vs. standard ones

Abstract

This project funded by the federal ministry of education and research from the research group 'Wind turbulence and its significance in the use of wind energy' handles a comparison between the load ranges for horizontal axis wind turbines resulting from different turbulence models, i.e. between the usual models as defined in the standards and a new model designed by Friedrich and Kleinhans. This should enable an evaluation of the relevance of this new model for wind modelling for wind turbines and if so, provide the community with new tools in wind simulation. Indeed, spectral models do not well reproduce extreme wind increments as met in gusts. Those models simulate using purely Gaussian statistics. However, measurements show that those increments do not follow normal statistics. The new model developed aims at correcting this problem. The turbulence models used are the Kaimal, von Karman and Mann models as defined in the IEC guidelines and the Friedrich-Kleinhans model, based on stochastic processes called Continuous Time Random Walks. The comparison is based on load ranges resulting from an RFC analysis of 100 time series obtained for 100 different seed numbers. Five wind speeds are investigated. The aeroelastic code used is FLEX5. The main conclusion that can be drawn from this study is that the non-Gaussian Friedrich-Kleinhans model produces loads that are significantly different from the loads obtained with the Kaimal model. That proves that the form of the tails of the increment distribution has a major influence on the loads of the wind turbine and should be considered when making fatigue calculations.